PDA

View Full Version : Well here goes... Aluminium frame router design



CharlieRam
15-07-2014, 11:48 AM
Hi all, I am currently still designing the machine, It will be made mainly using 20mm alu plate and 100x50 5mm box section, 20mm profiled rails sourced from chai (Thanks Jazz) and 1610 ballscrews hopefully belt driven.
Rail lengths are 1050 on X, 850 on Y and 350 on Z. Bearings are spaced 250mm apart on all axis (from outer dimension) which should give me an efective machining area of 800x600x100 excluding tool width.
Now I have used the gantry stiffness5 excel sheet and I think using the box section on the gantry I will end up with 13micron bending deflection and 30micron tool deflection. Would this be considered acceptable or the norm? If not Can you give me some Ideas to stiffen up the gantry design, I have attached a sketchup model in the zip file so feel free to modify and or tear it apart if you can help :-) Its obviously not complete yet but I dont want to spend hours on it if I am going in the wrong direction.
Will 5mm of aluminium be ok for the rails to attach to or should I glue some plate behind the box section for better securing.
One last question, I am hoping to use timing belts and pulleys, probably reduce the ratio to 75% so I should be able to get the speed for woods/ plastics but keep accuracy for aluminium, does that sound ok?
I look forward to some feedback, good :thumsup: or bad :sorrow:

Cheers, Charlie

CharlieRam
16-07-2014, 02:34 PM
Well, Quite a few views but no reply's so it cant be all bad, either that or everyone's enjoying the weather like I probably should be doing! more than likely though it is because of an incomplete design?
I have completed the basic design minus ball nut attachment and adjustable stepper motor brackets, pulleys and belts but I have some questions.

I was wondering about limit switches, Do they stop the machine dead or do I need to bring them in a bit from maximum travel and if so, how much?

Following on from that I may need to scale the machine up by about 100mm on X and Y, will the design still work or will I need to beef it up on the gantry?

I plan on using 1610 ballscrews for X and Y and 1605 for Z, is this correct.

To mount the 100x50 box section to the gantry sides I have a 40 x 40 bar cut to 90mm long in each end, would I be ok to countersink the box section and fasten with countersunk cap screws? I am assuming I can make adjustments with the cap screws on the gantry sides.

I have included an updated sketchup file, all components are models so it can be pulled apart bit by bit if you like, any feedback appreciated.

Thanks, Charlie

Lee Roberts
16-07-2014, 07:47 PM
Gantry looks to high and the X looks to wide.

.Me

CharlieRam
16-07-2014, 08:07 PM
OK, I can lower the gantry by 50mm by recessing the M/C bed inside the box frame, is that enough? what do you mean by X looks too wide, the width of x rails is 850mm between gantry side plates, I cant see a way of reducing that?
Thanks, Charlie

Lee Roberts
16-07-2014, 10:16 PM
Sorry I was on my mobile when I replied and it should have been a Z not an X, in relation to the width of the X the Z looks quite wide, so my thoughts where that you would be losing valuable cutting area by having the Z that size, but if your happy with the size of the cutting area you will get then it doesn't matter.

It was the same with the height of the gantry plates too really, if it was me I would consider dropping the hight down or adding another length across the X to help strengthen the whole thing up.

As I say I'm only looking at the pictures, I haven't downloaded anything.

.Me

JAZZCNC
17-07-2014, 02:30 PM
If your mostly cutting wood then this design will be fine but if your planning to cut aluminium often then I wouldn't use it.
For wood etc then the gantry height is fine and will be more than strong enough but with aluminium you need much more stiffness so I'd change the design completely.

Lee is correct about the Y/Z axis being a little wide for the size of machine.! 200mm is what I would use on machine this size.

Leave some room for overrun when placing limits because while they do stop the Control and software instantly inertia will push the axis and obviously the faster it's traveling the more it will over run. Asking how much is like asking how longs a piece for string.!!

Yes 10mm pitch on X & Y 5mm On Z. You won't need any ratio applied to the X & Y if you use decent drives and run them with good amount of volts. You'll easily it over 10mtr/min and you won't ever cut higher than that so don't waste time and money chasing speed.

Whats the frame and bed made from.?

CharlieRam
18-07-2014, 11:39 AM
If your mostly cutting wood then this design will be fine but if your planning to cut aluminium often then I wouldn't use it.


Yeah I thought as much, What about this one, I have also reduced spacing on Z and Y by 50mm giving the machine an effective travel of 800 x 650 x 150. I thinK this should be a lot more sturdy.
I haven't thought much about the base yet tbh, I was thinking of either having it mounted vertically to save space (if I decide to make X longer) or just build an aluminium 8040 table, I am assuming I will need to brace up the bed of the MC to stop twisting?
For the M/C bed I was going to use 15mm MDF and then place a 5MM aluminium sheet on top of that, drilled and tapped for t bar/ slots?
What do you think, Still not sturdy enough or will it work?

JAZZCNC
18-07-2014, 06:57 PM
Little better but still not what I had in mind if your seriously wanting to cut aluminium. Check out the forum for machines with base frames with sides raised and rails sat on top. This design is more router biased and it will cut aluminium no problem but not with the same abilty as machine aimed directly to do this.

Also that Z axis design is bad news. Again check out threads and look at Z axis designs that put the rails on the front plate and bearings on rear. Your design is a constant length lever that won't even reach the bed surface and will give the same amount of flex whether it's at the bottom of top of it's travel. With the other design the lever length is variable dependent on material thinkness or distance from tool.

MDF for the bed isn't ideal and I certainly wouldn't waste money putting aluminium on it. MDF changes shape from day to day so if your wanting accurecy then you'll need to surface it often. Personaly I'd try to find the most stable material you can afford for the machine base, Good quality ply will work then skim surface it flat and seal or put the aluminium on that. Then use MDF as a spoil board that you don't mind cutting away or into.

CharlieRam
18-07-2014, 08:23 PM
Little better but still not what I had in mind if your seriously wanting to cut aluminium. Check out the forum for machines with base frames with sides raised and rails sat on top. This design is more router biased and it will cut aluminium no problem but not with the same abilty as machine aimed directly to do this.

When you say ability, do you mean accuracy or chatter or what?, I did see the designs where the gantry sat directly on box section but I was trying to keep the footprint down to a minimum (Lack of space!) and I thought the angle brackets would give less flex than a box section, obviously not though. Would it help if I were to increase the size of the angle plates or would you still say box section is the way to go.
I will look at the Z axis, I never thought about doing it that way but now when I think about it, it makes sense thanks, I would prefer just ally for the base but its pretty damn expensive for a sheet that size, I will look into ply.
Thanks, Charlie

CharlieRam
18-07-2014, 10:39 PM
Your design is a constant length lever that won't even reach the bed surface
Just noticed this bit, It wasnt meant to reach the table because I was hoping to offset it with adjusting the spindle height and I left 150mm between base of gantry and M/C bed so I could hopefully fabricate a 4th axis on the unused part of the mc bed.

routercnc
19-07-2014, 10:28 AM
I Charlie,

I wrote the original stiffness v5 sheet that you mentioned in the first post a few years ago, plus later posted a v7 which may be of interest.

I've tried to replicate your results but cannot match them (don't know all the dimensions etc that you used). So I'll just make some general comments.

The 13um in Z is bending due to the spindle weight applied to the centre of the gantry. This seems fine to me.

The 30um in X sounds like you've only noted the 'tool deflection' number which is only the bit due to twisting. There will be a bit more overall deflection due to X bending to give you a final total deflection in X. This is starting to sound a bit high (30-40um is 0.03 - 0.04mm) for aluminium. However, this is at maximum extension so you can reduce this problem as you've stated by raising the job in Z.

Biggest thing to point out though is that you haven't run the analysis on the gantry sides (plates) in the Y direction. Depending on your exact numbers this is likely to be similar or greater than the X deflection and because it is just bending (you can ignore Y torsion) and there is no work-around in terms of raising the job in Z etc. This is because all the tool forces in Y go through the ballnut and this is at a fixed height above the X axis bearings. This is why Jazz keeps pointing you to the raised X axis designs for aluminium since this offset between ballnut and X axis bearings is basically zero. You are then free to beef up the bed/raised X axis sides to react this force.

I have a machine broadly similar to your posts so far and it will cut aluminium but I you can tell from the sound it makes and machine vibration that it is approaching the limit. If I was cutting aluminium more regularly then this machine would not do. For the occasional piece it is OK.

Finally, feel free to experiment with the spreadsheet but do just use it to get a feel for general comparisons and where to place effort and material. As a like-for-like comparison of different gauge, sections, and dimensions it will give you direction, but don't expect to get the quoted deflections out as there too many simplifications. So long as you use it as just another way of investigating the design (along with reviewing the build logs and the invaluable subjective opinions of experienced builders) then you will be OK.

Good luck with it and welcome.

CharlieRam
19-07-2014, 11:06 AM
Thanks for the info. The deflection was calculated only for one 100x50 5mm box section as in my first design, now there are 2 in an L shape.
This is meant to be a hobby machine so I honestly dont know how much aluminium will be cut on it but I do know I want to be able to cut so I will take the advice and modify the x sides to bring the y axis down.
Has anyone ever built the gantry with the carriages in a triangle formation? I am thinking if the 2 bottom cariages were 150mm apart and the top 2 were 250mm apart (from outside dimension) I could keep the same footprint and machining area?
Cheers, Charlie

JAZZCNC
19-07-2014, 03:12 PM
Just noticed this bit, It wasnt meant to reach the table because I was hoping to offset it with adjusting the spindle height and I left 150mm between base of gantry and M/C bed so I could hopefully fabricate a 4th axis on the unused part of the mc bed.

If I'm understanding you correctly then the Unused part is exactly that Unusable and putting a 4th axis there is pointless as you can't access it with spindle.? . . . . ( Edit: Ok Excuse that comment I'm not exactly firing on all cyclinders at the minute and realised you mean to put 4th axis head in that space and tail stock at other end running material down it's length.! . . . I was thinking material across the gantry.!!)

As for rest of machine then like I say it will cut aluminium no problem and if it's only occasionally and your not wanting perfection on the finish then it will be fine. If your wanting to cut deeper and get high quality finish the machine won't be stiff enough.
Personally I'd just go for it and if you find your cutting more aluminium than anything then build a machine just for this purpose because while a machine for cutting wood isn't 100% for Ali the same applies in reverse to some degree. Can't beat purpose built machines and Jacks of all trades always fall short in some department.

The bed and workholding on any machine can be a pain and often under estimated how important it is. This is esp true on machines that are intended to cut multi materials.
Problem comes from how you hold it down and the type of work and how you machine the material. If your cutting or drilling thru then having a nice aluminium bed isn't much use because it doesn't leave a nice warm fuzzy feeling when you chop into it.! So you need some spoil piece anyway and often this needs surfacing each time you use it if any decent accurecy is required.
Now IME the best bed is a combination of both.? So nice stable material for Machine bed that is surfaced parallel to the cutter with either all of it or part covered with sacrificial spoil board. If bed is large enough like mine is then having half n half works well and saves swaping between and surfacing for jobs that need the accuracy of the base.

CharlieRam
19-07-2014, 04:10 PM
Well ive started the redesign so no turning back now :-) and tbh I think I will mostly be machining metals more than plastics and wood so I may as well make it right. I have changed the z axis but that may well of mucked up my plans for the 4th axis as the spindle plate and rails come down now!
I will try and get the plan finished and post it up so you can all tell me why it wont work again!
Thanks for the help and advice
Charlie

CharlieRam
20-07-2014, 03:10 PM
Here goes, My 4th design with base, The base is made mainly with aluminium 2" x 2" 1/8th thickness with some 1 3/4 bar inserted at the bolting points (not added in yet) I will also have adjustable feet, do you think it will be strong enough or does it need beefing up.
Also my redesigned gantry again! :-) there will be a 15mm plate across the back for the X stepper and pulleys to attach to but I thought I would post my plans before I start adding in all the details such as bolt holes etc.
As before, feedback good or bad appreciated.

Thinking more about the frame, I don't like it so maybe I will have to learn welding. My dad used to do it years ago and he's retired now so maybe I can get him onboard.
Where is the best (read cheapest!) place to get cut to length steel including mitre cuts or would I be better ordering full lengths and investing in one of these:
http://www.screwfix.com/p/evolution-rage3-s-210mm-sliding-compound-mitre-saw-240v/60839#
Its £100 but says it will cut steel, ally, wood and whatever.

CharlieRam
21-07-2014, 12:17 AM
Another question, Do all these plates need to be 20mm, If I make them 15mm will it affect the machining ability substantially? I'm on a cost/weight cutting exercise!

JAZZCNC
21-07-2014, 04:24 PM
Another question, Do all these plates need to be 20mm, If I make them 15mm will it affect the machining ability substantially? I'm on a cost/weight cutting exercise!

Well first I'd dump the gantry back plate as it adds nothing but weight with very little strength gain and unless perfectly machine and setup could cause you all sorts of trouble with bearings to binding up.!
350mm rear plate and bearing plates etc could be 15mm but wouldn't change the front plate.

Don't go chasing weight it will be your friend when cutting and if you need really high speeds with high velocity changes then put the correct motors on it and you won't have any trouble.

CharlieRam
21-07-2014, 04:29 PM
Well first I'd dump the gantry back plate as it adds nothing but weight with very little strength gain and unless perfectly machine and setup could cause you all sorts of trouble with bearings to binding up.!
350mm rear plate and bearing plates etc could be 15mm but wouldn't change the front plate.

Don't go chasing weight it will be your friend when cutting and if you need really high speeds with high velocity changes then put the correct motors on it and you won't have any trouble.
Actually that back plate is connected to the ball nut so without it my Y axis will go no where!

CharlieRam
23-07-2014, 12:12 PM
Also that Z axis design is bad news. Again check out threads and look at Z axis designs that put the rails on the front plate and bearings on rear. Your design is a constant length lever that won't even reach the bed surface and will give the same amount of flex whether it's at the bottom of top of it's travel. With the other design the lever length is variable dependent on material thickness or distance from tool.


Hi Jazz, is that Z axis any weaker the way I had it? I am struggling for room and didn't want to compensate by reducing my cutting area, I have gone back to Idea 3 but raised the rails on X. I would still like to use the fourth axis along X and this would allow that, giving me an effective work area of 150mm diameter by whatever length travel I decide on.
My X rails are 810mm apart, carriages are 250mm apart from outer dimension, Would I suffer from binding if I just had a central ballscrew or would you still recomend one on either side?
Thanks

njhussey
23-07-2014, 01:02 PM
The normal convention for the Z axis is to have the rails on the front plate and the carriages/bearings on the back plate. This adds stiffness to the front plate which is where the axis most needs it. Also stick with 20mm plate if you can rather than 15mm. With regards to ballscrews two are way better than one, you undoubtedly would get racking with one central ballscrew at that width I would say.

CharlieRam
24-07-2014, 02:34 PM
Okay so what if I were to make the spindle plate 30mm thick aluminium or 20mm+ thick steel ( I could grind the steel perfectly flat and parallel at work, well within a couple of microns anyway), would that be strong enough to have the bearing blocks the opposite way round or does that method just not work? in fact a lot of the plates could be made of steel which would be easier for me to grind flat as we use mag chucks, it would add weight but also a lot of strength.

Probably dont want to change too much though as the weight will increase substantially!

CharlieRam
25-07-2014, 07:40 PM
Anyone? Is My idea 3 Z axis just not up to it, will changing the front plate to steel help or not? Just the Z plate, not the x rails as I have mounted them directly on top of the rails.

routercnc
27-07-2014, 03:51 PM
Hi Charlie
I think you are not getting a reply on the z plate as most people have it set up in reverse (carriages on Y plate) so can't give you an opinion.
If you want to go with the opposite (carriages on Z plate) then you'll need a calculation of 20mm aluminium with reverse mounting (at full reach and home-they will be different which is why that route us preferred) vs forward mounting with 20mm steel and 30mm aluminium (at any reach as they will all be the same stiffness).
if I get the chance I'll have a look tonight and see if you can recover the stiffness through gauge.
What is the distance from the lowest Z
axis bearing to the collet at full Z extension?

routercnc
27-07-2014, 09:49 PM
Hi Charlie,

OK, I've made a few assumptions for dimensions and compared different Z axis options for deflection. The deflections are artificially small because the rest of the machine is grounded, but you can compare the numbers with each other to see the trends.

1. Shows the conventional layout (carraiges on Y axis plate, rails on Z plate) using 20mm aluminium plate at full extension. This gives 10um.

2. Shows the same conventional layout as 1 but at almost minimum Z extension. This gives 0.2um. This is 20x stiffer just by raising the job so that cutting is done with the Z axis near the home switch.

3. Shows the unconventional layout (carraiges on Z plate, rail on Y plate) using 20mm aluminium plate. This is drawn at an arbitrary extension because with this design all extensions have the same stiffness. This gives 10um. You can see that it is the same as 1. But if you need to do a deep cut, or hold a fine tolerance etc. then you cannot raise the Z to increase the stiffness. So, onto your question about recovery . . .

4. Shows the unconventional layout using 30mm aluminium. This has reduced the deflection to 3um. 3x better than 20mm aluminium, but still nowhere near the best conventional result (2).

5. Shows the unconventional layout but using 20mm steel for the Z plate. This has a deflection of 3.5um, so about the same as the 30mm aluminium plate. This is also nowhere near the best conventional result (2).

So, if all of your cutting is done near full extension, and your machine is stiff enough to cut well at that extension, then it does not matter if you choose conventional or unconventional (and both with 20mm aluminium plate) as they are the same.

But chances are you might not get the finish you want at full extension as you are cutting at quite a distance from the support bearing, and so with the conventional layout you can raise the job in Z and try again. You can stiffen the axis quite a bit by doing this. With the unconventional layout this makes NO difference (in terms of Z plate bending) so you are stuck with it. You can upgrade the Z plate from 20mm to 30mm aluminium and stiffen it a bit more, or go for 20mm steel (works out about the same), and gain an improvement. But you cannot get close to the stiffness improvement of the conventional layout raised close to the home switch.

I can't tell you which option will be stiff enough for you, but I can say that once you have made the machine if you run into problems and have gone the unconventional route it is difficult to make a significant improvement. Hope this helps.

12912

CharlieRam
29-07-2014, 03:46 PM
Hi Charlie,

OK, I've made a few assumptions for dimensions and compared different Z axis options for deflection. The deflections are artificially small because the rest of the machine is grounded, but you can compare the numbers with each other to see the trends.

1. Shows the conventional layout (carraiges on Y axis plate, rails on Z plate) using 20mm aluminium plate at full extension. This gives 10um.

2. Shows the same conventional layout as 1 but at almost minimum Z extension. This gives 0.2um. This is 20x stiffer just by raising the job so that cutting is done with the Z axis near the home switch.

3. Shows the unconventional layout (carraiges on Z plate, rail on Y plate) using 20mm aluminium plate. This is drawn at an arbitrary extension because with this design all extensions have the same stiffness. This gives 10um. You can see that it is the same as 1. But if you need to do a deep cut, or hold a fine tolerance etc. then you cannot raise the Z to increase the stiffness. So, onto your question about recovery . . .

4. Shows the unconventional layout using 30mm aluminium. This has reduced the deflection to 3um. 3x better than 20mm aluminium, but still nowhere near the best conventional result (2).

5. Shows the unconventional layout but using 20mm steel for the Z plate. This has a deflection of 3.5um, so about the same as the 30mm aluminium plate. This is also nowhere near the best conventional result (2).

So, if all of your cutting is done near full extension, and your machine is stiff enough to cut well at that extension, then it does not matter if you choose conventional or unconventional (and both with 20mm aluminium plate) as they are the same.

But chances are you might not get the finish you want at full extension as you are cutting at quite a distance from the support bearing, and so with the conventional layout you can raise the job in Z and try again. You can stiffen the axis quite a bit by doing this. With the unconventional layout this makes NO difference (in terms of Z plate bending) so you are stuck with it. You can upgrade the Z plate from 20mm to 30mm aluminium and stiffen it a bit more, or go for 20mm steel (works out about the same), and gain an improvement. But you cannot get close to the stiffness improvement of the conventional layout raised close to the home switch.

I can't tell you which option will be stiff enough for you, but I can say that once you have made the machine if you run into problems and have gone the unconventional route it is difficult to make a significant improvement. Hope this helps.

12912

Cheers for that, I am in Egypt atm and the internet in my hotel is dodgy as hell. I will have a play with that spreadsheet (is that the stiffness v7) when I get back because I think the distance to the collet from bottom bearing block is quite a. Bit smaller than 150mm and consistent stiffness should give more predictable results. Cheers

routercnc
29-07-2014, 08:31 PM
Hi Charlie,

OK, enjoy your visit. I wrote this sheet just for your problem.

I've now added it to v7 and created v8. Posted here so you can have a play.

Thanks

Boyan Silyavski
31-07-2014, 11:52 PM
Hi,
Maybe my build log will be of interest to you and especially the way I made the z platehttp://www.mycncuk.com/threads/6457-Sturdy-and-Fast-all-Steel-CNC-my-first-build?p=59627#post59627
I intended to do it from aluminum but instead did the z from steel plate. It's extremely strong extended and compact.
My advice- draw it but do it when you have in your hands the ball screw nut, as it happens they can send you a slightly different housing than at the listing. It happened 2 times to me. Same for the spindle bracket, as they cast it sometimes the holes are not where you expect to them to be. Chinatown ��

CharlieRam
13-08-2014, 11:41 AM
Well I'm back I had a play with that spreadsheet and decided to stick with my unconventional layout, the reason being is I have used calculations based on 35mm thick steel plate, this is the 20mm thick plate plus the 15mm thick spacers, I was thinking of gluing and screwing them together but I am not sure if this will give the same results as a 35mm thick plate with a recess machined for ballscrew.

Anyway, the figures from that spreadsheet give me roughly .65 micron deflection, the conventional is slightly better at .19 microns but a lot worse at full extent with 10 microns but if I reduce my cutting depth to just 100mm by raising the bed and spindle by 50mm then I get .19 microns across the full cutting height!

I am a bit stuck at the minute though, am trying to figure out how to drive the X ballscrews from a single centrally mounted motor but leaving the ends of the M/C open for any job overhang I may need. It seems like I may need a lot of pulleys to guide the belt but I am not sure it is a very elegant solution, Any Ideas or am I just going to have to go with twin motors?

I do want to add a 4th axis at some point and I don't want to go silly with the spend on adding unnecessary motors and drivers if they aren't needed, speaking of which, I have drawn the base up now and I'm thinking of having a go at welding but last time I tried that it looked like pigeon shit! How much should I expect to pay to have one fabricated?
I have added some more sketchup images, the steel parts are colored blue.
As before I look forward to your criticism/Acclaim:crushed:
Thanks, Charlie

EDIT. Also checked the gantry sides stiffness using the calculator using height to top of gantry as 235mm but it assumes the 20mm plate is not braced, Mine has plates on the back bolted to the bearing block plate, the gantry plate and also the gantry beam so can I just reduce the length in the calculator so it reads full length minus the brace plate giving me a total height of 103mm to give a realistic figure?

CharlieRam
14-08-2014, 11:29 AM
Just been having another play with the stiffness spreadsheet but I couldn't figure out what to select for my gantry type, I have done the special type but the deflection value isn't shown in yellow as stated and also not selectable in the gantry type drop down menu?

routercnc
14-08-2014, 05:21 PM
Hi Charlie
The gantry side stiffness calculation is for simple routers without raised X axes. It is to help determine whether to use plate, box etc for the sides and what thickness
You have the vastly superior raised X axis design ( which wasn't that popular when I first wrote the sheet) and so isn't relevant for you. Your gantry sides will be fine as they are.

CharlieRam
14-08-2014, 07:12 PM
Cheers for the help. I suppose it's time to lock down the design and start adding all the fixing points and decide how i'm going to run the timing belt for the X axis.
Thanks again,
Charlie

Boyan Silyavski
15-08-2014, 12:42 AM
I would use one belt only, as its easier to align properly. Make sure the idler pulleys not to bend. I would encase them so every steel pin is supported at both sides. Makes one of the idles a tensioner. Find the Gates belts site and there were calculations how to tension the belt using a guitar tuner if you dont have proper device to measure the tension.
Mistakes here will affect the performance, especially the precision. Belt must be tensioned properly, not by feel.

JAZZCNC
15-08-2014, 09:55 AM
I don't care what the spread sheet says or the calculations it will be Mistake to go with the unconventional Z axis you will be creating a tuning fork and this will show in the finished cut guaranteed.!!

Regards the belts then problem with one long belt arranged like this is you can't get enough tension on it with out applying pull on the screws and it becomes unwieldy belt length because you have to make sure the motor pulley as enough teeth engaged and this often means longer belt.
So I'd be more inclined to have 2 short belts going from screws to rotating idler shafts so can get nice tension on screws then longer belt to same shafts on another set of pulleys that you can get good tension on the belt using motor as tensioner. (like doodle in pic) More expense and time but will be better than one long belt.
13110

To be honest it's far easier and stronger for machine to run a brace across back then just one belt can be used. In practice you'll more than likely find you never put any thing on bed that it gets in way off and you can still pass long boards thru.
It would also mean you can lift the ballscrews back up closer to gantry which will stiffen it up slightly and make easier to build.

CharlieRam
15-08-2014, 12:16 PM
I was thinking of going that way for the belts but it just seemed a bit unwieldy. Can you tell me why you think it will act like a tuning fork, have you made one like it before? Is it because I am using steel plate or is there another issue going on that i cant see?

One thing worth noting, at work we grind thin walled exotic alloys like inconel and waspaloy and they really do resonate whilst machining, we get around this by using a glorified elastic band and it reduces the vibration drastically which got me thinking about the rubber floor mats you can get for playgrounds. If I were to use strips of that glued to the metal plate in stategic positions then that should help with dampening if that is the issue, What do you think?
Cheers

JAZZCNC
15-08-2014, 01:54 PM
Can you tell me why you think it will act like a tuning fork, have you made one like it before? Is it because I am using steel plate or is there another issue going on that i cant see?

One thing worth noting, at work we grind thin walled exotic alloys like inconel and waspaloy and they really do resonate whilst machining,

I have made many Z axis but only ounce did I build one this way and that was due existing design issues(not my design), it was for a machine which exclusively cut HDPE so no big deal but the difference between my normal conventional way was clear when pushed hard.

The differnece between this and your work example is that the work machine didn't vibrate the material did which happens now imagine what would happen to finish if the tool was vibrating as well.! . . How do you stop or deal with that.? . . . . . Cut slower/shallower point being your making compromises you shouldn't have too just becasue of machine design

CharlieRam
15-08-2014, 02:12 PM
Maybe i am being thick but i cant see how flipping the rails will introduce vibration, looking at the conventional method then the spindle is mounted away/lower from the bearing blocks whereas my design is a constant length of zero from the base of the spindle clamp to the bottom of the bearing block. Is it the spindle clamp causing the issue or is the spindle too low in the clamp? How low can the spindle be in its holder?

Also think i may use a plate across the back of the machine like you suggest, I suppose one open end is enough if I need any overhang
Cheers

CharlieRam
15-08-2014, 04:55 PM
The compromise i am making is due to lack of space for the M/C vs. Large enough work area. With this design the total width is about 900mm with the other it was about 1100mm. I havnt even got anywhere to put the machine yet, I have an area of 2m x 5m behind my log cabin which i plan to build a soundproof ish shed with concrete base for the machine, it will then run lengthways leaving me roughly 1m workspace to pass the machine, the other design will only give me about 800mm which is just too small.
TBH i am building this machine to prove i can and to give me something to do. It may well never even nachine ally but then again i might dream of all sorts of wonderful things to make. Who knows? :-)

Boyan Silyavski
16-08-2014, 12:48 AM
Maybe i am being thick but i cant see how flipping the rails will introduce vibration, looking at the conventional method then the spindle is mounted away/lower from the bearing blocks whereas my design is a constant length of zero from the base of the spindle clamp to the bottom of the bearing block. Is it the spindle clamp causing the issue or is the spindle too low in the clamp? How low can the spindle be in its holder?
Cheers


Whatever you do if you dont:

-use long size 20 bearing blocks
-space the bearings that the front plate slides on at least 260mm from outside ends/each long block is 90mm long/
-fix the rails on the front plate back

you will finish with a machine incapable of working Aluminum and maybe not so precise on hard woods.

There not so much to understand, the rails +the bars they rest form ribs that prevent long axis bend. That simple.

Front plate must be 12mm steel backed with steel bars below the rails, or at least or 20mm aluminum backed with aluminum bars. Using 2 spindle brackets would make things even better as the spindle will add stiffness.

Linear rails are cheap, so that will add very small amount to the build. See 200mm travel axis made same way as we speak that reaps/i can not help say it :frog:/ fully extended , through aluminum without any chatter . here (http://www.mycncuk.com/threads/6457-Sturdy-and-Fast-all-Steel-CNC-my-first-build?p=59627#post59627) post #109 and how looks finished from 12mm steel plate a bit up at the same page

CharlieRam
16-08-2014, 12:18 PM
Hi Silyavski, the rails and bearings are 20mm profiled from chai, they are 75mm long plus 15mm for grease nipple which I haven't added to my sketchup model yet. I originally spaced the bearings 250mm apart from outer dimensions but was told 200mm was fine, this then gave me 150mm depth of cut instead of the original 100mm I planned so I have no issue going back to 250mm spacing if it will help.

The front Z plate is 20mm thick steel with 15mm X 50mm steel spacers glued and bolted to the plate and then the carriages are bolted onto this, the way I see it is the spacers should give me the added rigidity, would it help if they were surface hardened to make them stiffer because that is the only difference I see between having the rails mounted to the Z plate.

I am just finding it hard to understand why flipping the rails will introduce vibration as dean stated and I can't understand how the plate can bend as it has the bearing blocks on each corner. I am planning on having two spindle clamps as you suggested, in fact, it was there on earlier iterations, I must of deleted it!

Jazz, yes it is the workpeice that resonates in my example but the rubber absorbs a lot of it and I am thinking if I tensioned the rubber over the front of the Z plate it would absorb some of the resonance created in the steel Z plate if that is indeed the issue (steel instead of ally?).

Thanks, Charlie

Boyan Silyavski
16-08-2014, 12:54 PM
Given the short length of your desired travel it will work ok. Bus as you have drawn it, the bit should touch the finished machine bed. Cause lower it will not go obviously. Is it so?

The case is if say you want it to travel 200mm for example or longer , then the 4 blocks on the Z will go higher than the gantry, hence the tuning fork.

CharlieRam
16-08-2014, 01:50 PM
The case is if say you want it to travel 200mm for example or longer , then the 4 blocks on the Z will go higher than the gantry, hence the tuning fork.

So, is that the issue that will cause the vibration, the rails going above the gantry top? If it is then I will have a look at what I can do.
Cheers, Charlie

CharlieRam
18-08-2014, 01:34 PM
Well... I'm at a bit of a crossroad in my design, I have altered the Z axis to the conventional method which should please Jazz! but the machine is now 1004mm wide by 1400mm long with overall cutting area of 620mm x 1100mm and I'm now thinking do I need it that big?
The original idea was to have a machine capable of machining soft metals or even steel if it could cope but I also wanted it to be big enough to machine 600mm wide sheets of MDF so I could machine my arcade cabinets, the problem is I would need a machining area of 1800mm lengthways to produce them in one cut but I am now thinking should I make a smaller machine with say a cutting area of 400mm x 600mm for aluminium and possibly steel (Is steel doable or a definate no go?) and when that is built, use it to make parts for a dedicated mdf/wood router that would take the full length sheets at a later date, This machine could hang of the wall with a slight incline to get over the space issue.
I am also thinking that 1610 ballscrews with 1.8 deg steps will only give a resolution of 0.05mm, If I built it for metals and plastics then 1605 ballscrews could be used bringing the resolution down to 0.025mm.
What are your thoughts on this?

One other thought, If I only have a cutting width of 400mm would I get away with a single ballscrew, if not, what is the maximum width I could get away with or is it just better to go with 2 when machining metals?
Cheers, Charlie

irving2008
18-08-2014, 05:18 PM
For machining metals, esp steel, you need rigidity, so a mill arrangement, table that moves in X & Y and a rigid fixed Z column is the best solution. a rigid router style machine can mill ali if strong enough but its a compromise at best.

To improve resolution for machining metal you need to gear the motors down. a 4:1 reduction improves resolution by 4 and increases torque, necessary to overcome the inertia of a heavy moving table and increased cutting forces.

Boyan Silyavski
19-08-2014, 08:25 AM
Single ball screw is out of question if you machine metals on the cnc, meaning aluminum, not steel. many though machine iron from time to time. Steel is out of question if not annealed.

1610 ball screw makes one turn and moves 10mm. so for 1mm it makes 1/10th of turn. To make one turn a 1.8 degree motor- 360/1.8=200steps per turn. When you apply 1/8 micro stepping which is the usual 200x8=1600 steps per turn.Any decent driver will do that. So to move 1mm then 1600/10=160steps per turn. 1mm/160steps=0.00625mm resolution. 1/4 microstepping will give you 0.0125 mm resolution

I would worry more about rails and ball screws parallelism and perpendicularity in all directions, as this is the culprit for the real life imprecision of a machine. Do yourself a favor and equip with precision straight edge long enough that can be laid on both the long axis rails perpendicular, and 2 precision squares, cause without this i dont see how you can even be in the <0.5mm ballpark when you reach the moment to mount everything together.

JAZZCNC
19-08-2014, 09:28 AM
I am just finding it hard to understand why flipping the rails will introduce vibration as dean stated and I can't understand how the plate can bend as it has the bearing blocks on each corner.

Charlie it's not rocket science mate. It's all about leverage and vibration. Quality of finish mostly comes from trying to get the lowest amount of vibration at the tool. So we use the shortest tool we can with the least amount of stick out from the spindle to shorten the lever.

Your design is a very long constant length lever that never changes no matter what depth we cut.? Your lever length is distance the spindle extends from the spindle mount plus the tool extension. Lets say total extension of 150mm.

Now if you swap the rails around your lever is variable length lever and only ever reachs 150mm when cutting really thin material and at full extension.
Every where in between and the leverage drops and the stiffness increases so there's less deflection at the tool. At full height our extension is pretty much just the spindle nose and the tool length so order of magnitude better than your design.

May seem like a small thing to you but it makes all the difference when things get hard.!! . . . . Your design is ONLY good for wood anything harder will show it's weakness quickly.
Also with your design then using thick steel for the back plate will add very little to the design other than making the Z axis motor work harder lifting more weight. Your gaining very little strength over aluminium because it's supported at the 4 corners and not extending, if it was extending like a lever then yes it would give more strength.

Regards the size and use of machine then I'll repeat what I've said many many times it's always best to build a machine designed to do the job intended and do it the best it can. JACK of ALL TRADES is always a compromise in some department and this compromise increases with size.
Small machines do it best because they are easier to OVER build.!

routercnc
20-08-2014, 09:42 PM
Hi Charlie,

Good to read that you've switched to the conventional Z axis, although I hope you've done it due to understanding the problem rather than peer pressure.

To to lay it out again, using the calculations for the simplified example previously shown:
Conventional Z axis deflection of between 0.19um - 10um depending upon Z axis extension
Unconventional Z axis deflection of 10um - FIXED (i.e. the worse case conventional at all times)

Your unconventional sketch in post #39 looked like it might get around the 'tuning fork' problem but it would not be very practical as it was drawn at full extension and this meant cutting would be up near the gantry! Your only option for practical work would be to drop the spindle down in the mount to hang down out of the clamp, but I think this would not be especially stiff. Your only other option in the design would be to raise the lowest bearing block to allow the Z axis to drop further but then you are back around the loop of an unconventional Z axis as per the above.

CharlieRam
21-08-2014, 09:07 PM
Hi Charlie,

Good to read that you've switched to the conventional Z axis, although I hope you've done it due to understanding the problem rather than peer pressure.

Hi, TBH I changed because that many people can't be wrong...Can they? :-P
I understand what they are saying, although I don't fully agree because although with the conventional method at miniumum travel it is stronger because the tool tip is about 40mm from the bottom bearing block, at max travel it would be far more flimsy than my design, there must be a 'magic' point on Z where aluminium can be machined ok and if I knew that distance then I could try and work it out in my design.

None of that matters now ( I think!) because I have gone back to the drawing board with a completely different design using a fixed gantry based off a Video Jazz posted in another thread where the Y axis raises and lowers with Z. It may come to nothing and I may change my mind again!

Jazz, I know what you say about jack of all trade machines, it would help if I knew what I intended to use the machine for but I don't! I like working with wood as much as metal, I think now I am leaning more towards metal machining because more practical things can be made but I would also like to have a play with my artistic side with woods and plastics, This was why I was going for a router type build initially but the size required for some of my wood type projects have put a bit of a dampener on that :-( unless I go for a vertical machine like yours.
Cheers, Charlie

JAZZCNC
21-08-2014, 11:09 PM
Hi, TBH I changed because that many people can't be wrong...Can they? :-P
I understand what they are saying, although I don't fully agree because although with the conventional method at miniumum travel it is stronger because the tool tip is about 40mm from the bottom bearing block, at max travel it would be far more flimsy than my design, there must be a 'magic' point on Z where aluminium can be machined ok and if I knew that distance then I could try and work it out in my design.

Well don't be put off by anything we say and always go with your gut feeling I would say. but I'll tell you now thru experience not guessing that your wrong.

There is a magic number.? On my machine.!! It's 0-50mm and past this finish deteriates to point that's not acceptable to me, but that doesn't mean my number will match your machines number.!! . . . . This is essentially the problem in that every machine is different and the finish you get will be a direct results of how strong and how good the design along with many other variables. This also holds true for feeds n speeds to some degree.? Each machine will perform different for same material.!


None of that matters now ( I think!) because I have gone back to the drawing board with a completely different design using a fixed gantry based off a Video Jazz posted in another thread where the Y axis raises and lowers with Z. It may come to nothing and I may change my mind again!

If it's the one I'm thinking about then it's a good layout and very strong. I've got a much larger version part built using 150mm box section for my self just can't get around to finishing it. (Well it's more starting than finishing.!!)


Jazz, I know what you say about jack of all trade machines, it would help if I knew what I intended to use the machine for but I don't! I like working with wood as much as metal, I think now I am leaning more towards metal machining because more practical things can be made but I would also like to have a play with my artistic side with woods and plastics, This was why I was going for a router type build initially but the size required for some of my wood type projects have put a bit of a dampener on that :-( unless I go for a vertical machine like yours.
Cheers, Charlie

If your going for metal then forget the moving gantry design. Go with the design above and make it massively strong. To be honest if your wanting to cut metal then I'd suggest you keep an eye out for a large Milling machine and convert to CNC or look for used or knackerd CNC VMC and convert to Mach3/Linux cnc.
Only few weeks ago there was a Cincinnati CNC VMC on ebay for £1400 24 tool changer and full bag of tricks. At that money even if screws and rails where worn out you could convert control and replace components for same money or not much more than building a DIY machine for cutting steel.!

To give an example I picked this CNC Mill up at scrap value. 1100 x 500 x 500 cutting area. DC servo's, 7.5Kw Cat40 spindle, Was fully working apart from needing PSU for the out dated Hindeman control which at some point around 2060 when get time I'll be replacing with Mach3 and CSlabs Analog controller. DIY isn't always the best option esp when you get into milling steels.!
1316313164

CharlieRam
22-08-2014, 02:07 AM
I see three problems with buying a mill.

1. I couldn't say I made it myself ( big one)
2 It's bloody huge! I would never get it in my back garden and even if I did, I wouldn't have anywhere to put it.
3 Divorce is expensive :-)

Cheers, Charlie

JAZZCNC
22-08-2014, 09:52 AM
I see three problems with buying a mill.

1. I couldn't say I made it myself ( big one)
2 It's bloody huge! I would never get it in my back garden and even if I did, I wouldn't have anywhere to put it.
3 Divorce is expensive :-)

Well easy replys's to these Commnets.!!

#1 It would be an achievement in it's self for someone new to CNC to Retrofit something like this and they could be proud if they did it.!
#2 This should tell you everything you need to know about what's required to cut steel.!! . . . . It's nearly 3000KG and mostly cast iron.
#3 Turned out to be the Best thing that ever happened and worth every penny(And there where many 1000's. . Lol).:thumsup:

CharlieRam
02-09-2014, 12:38 PM
Well....
Ive changed my mind again! not sure whether to start another thread now.
I have decided that I am going to buy a mini milling machine for machining steels and simple plates ect which will help me build my router which will therefor be used mainly for woods and plastics with maybe the occasional bit of aluminium if I decide to convert the mill, I am thinking something like the ama25lv, its about the right size to get behind my shed!
This means I am back to idea 6 albeit with a conventional Z but I have measured the area where I am building my 'workshop' and once I have fitted soundproof / insulation I will be left with a working area of about 1.6m wide by 4m long. If i install my router flat then that will leave only 60cm at best to get past the machine, Is this too tight? it could be quite dangerous with the gantry swinging back and forth!
My other option would be to install it against the wall length ways or height ways and bolt to the floor, height ways would work best for me but that depends on the recomended gradient and the lump of concrete its bolted to!
Can you take a look at my Y carriage arrangement and let me know if it will be OK, I moved the lower carriages together by 50mm and the upper ones 50mm further apart so it utilises the space on top of the beam and gives me some of the movement back which was lost by using the conventional Z.
Things to do:
1. Build my shed/workshop
2. Buy a milling machine
3. Build my router!
4. convert the milling machine?

Cheers, Charlie

CharlieRam
08-09-2014, 04:32 PM
Well here it is, Idea 9 :worked_till_5am:, mainly for woods/plastics but also hoping to do a bit of aluminium or cast iron work when I modify my mill (which I havn't actually got yet! :eagerness:)
All bits in blue are steel, the gantry is built using 80x40 4mm box section aluminium with a 20mm plate across the front, the X axis rails will be 80 x 40 steel with 5mm of resin for leveling but I am not sure whether to go 3mm or 4mm steel thickness (is 3mm enough, I will go 4mm if its weldable??) the frame is 50x50 3mm steel and I plan on putting 4"x1" aluminium box section running the length of the bed with a 10mm alu plate on top of that drilled and tapped.
To manufacture the gantry I plan to machine the front plate, leaving a little for finishing. The aluminium box section will then be bolted together, solid aluminium blocks will be machined to fit in the ends. I am then hoping to lightly skim the X rail seating faces square to the front face and also lightly skim the front face before attaching the 20mm plate. I will then skim the profile rail support faces on the alu plate. What do you reckon?
The frame and X rails are all one component and even though I haven't welded before I am hoping to get the top face for the rails within 5mm so that the epoxy leveling will do its job! I realize that I am going to have to shim the ballscrew mounts so that they run parallel with the rails but is there anything else I should watch out for?
I have included the sketchup file for anyone wanting to tear it apart for scrutiny and as always appreciate any feedback as to why it will/won't work.
Cheers, Charlie

Boyan Silyavski
08-09-2014, 05:50 PM
I wouldn't put that profile at the back, that limits larger pieces. Instead cut 2 more small side pieces and reinforce the last one of the stair steps at the back of the table, welding a pack of 2 together. Same for the front. may be even one more at the middle. Or reinforce back and front with additional plates.

How long and how wide is the table? may be if you remove what i say you will need adding it bellow, even at front also. Depends on your priorities. Tough i see at the other hand you use a lot of diagonals, so that last may be not necessary.


13340

CharlieRam
08-09-2014, 06:45 PM
The machine overall size is 950 wide by 1550 long with a cutting area of 610mm x 1300mm x 150mm
The upper cross brace is also used to mount the stepper but I can add more strutts between the x rail and 50mm frame if thats what you mean?

ba99297
08-09-2014, 08:20 PM
Hi
First of all be polite with my English

About your plan
I think that the tube where the rails rest, should be wider (60mm at least ). When you apply the epoxy you will need 20mm for the rail and 15mm-20mm left right of the rail for the meniscus effect ( the tension that has the epoxy at the edges ) . So your tube should be at 50-60 wide minimum)

At the top view I saw 8 diagonal braces. I think you will need only 4 at the edge corners.
I see that you have the y axis ball screw at the middle protected by a plate. Think how you are going to work install and adjust the ballscrew as many time we think “I will think about it later” and finally you find out that you cant even bolt is in place”


Things you must be careful (others told me do so and they are right)

Spot weld in order not to produce too much heat. Even with 80X80X4mm distortion is an option ). After the frame get a first shape you can make bigger welds, no more 3-4 cm at a time. I know everybody want to make big weld with many amperes at the arc welder but this produce too much heat.
Try to be as accurate as possible at every step, even if you finally apply epoxy. Of course don’t make excesses.


It is very similar to mine machine that I design for about a year and start to build 2 months ago


My build starts at page 12 of the thread

http://www.mycncuk.com/threads/6674-Stell-frame-cnc-1500X1000-Adjustable-table-your-opinion-please/page12

My main specs are
80X80X4mm tube for frame and gantry (gantry at the middle has a piece 120X60X3mm )
80X40X3mm steel tube for the bed.
Working area
750 X 1400 X 180mm

4 Yaskawa 400 watt servos (2 for x axis )
20mm profiled rails

The design of the table was mainly based on syliavski construction.
Also the one who help me most is Dean. I change my mind many times, I get the basic idea for the table from Syliavski, Dean answers all my questions and I think that I make a good start. Of course i made mistakes. I think it is very difficult to avoid mistakes at the first construction. It is very important to have people that inspired you by their ideas, also people who are there to help whenever you have a question.It would be wrong if I didn’t mention the help of Jonathan for his servo size calculator, and Eddy Current for his information and all the people that ansewr to my thread.

Finally I want to suggest you to think how you are going to move that monster. First things are easy but as you add weight it would be difficult to move and turn the frame. Mine now is nearly 250kgr. If I didn’t install a winch it would be a nightmare to move it. You can see the photos to understand what I mean

. http://www.mycncuk.com/threads/6674-Stell-frame-cnc-1500X1000-Adjustable-table-your-opinion-please/page13


Have a good start

Vagelis

CharlieRam
08-09-2014, 08:55 PM
Hi, I did read about the meniscus effect but I am sure I also read that 10mm either side was enough which is why I went for the 80x40, I could lose the 4 inner angle braces and possibly use the spare material to add another cross brace. It is very similar to your design except yours looks a lot stronger, my ballscrew is actually bolted to the front ecocast plate and so 'should' run parallel to the rail front face meaning I only have to adjust up/down, a couple of holes through the box section gantry should enable me to adjust that unless you can get bearing supports that are threaded?
Yes the frame will be heavy but not as heavy as yours, I will need one length of 80x40x4 and 2 lengths of 50x50x3 which I believe will come to just under 120kg, that is without ballscrews etc so should be managable for a couple of people.
I've never welded anything before so I will be practicing first but I have read about spots and little bits at a time so wish me luck on that!
Cheers, Charlie

Boyan Silyavski
08-09-2014, 11:52 PM
Yes,about the epoxy, the 10mm at each side is ok, given that you weld to the mm the frame.

i also am wondering about that diagonals and at the same time big holes in the middle. I don't know the top you are planning on but generally i wouldn't have a hole in my table bigger than 300mm, otherwise you will need 50-70mm top if made from ply or similar. even alu top would benefit from such maximum distance.


IMHO you are mistaken about the ball screw end mounts. Do yourself a favor and design it similar like i did them from 10mm plate and additional plates that screw to that perpendicular reinforced with ribs plate.
Or you could find your self in a scenario that you have to file shims or even worse, what you will do if the ball screw has to go inside direction?
I believe the way i did it was simpler especially for precise alignment of the ball screws. Meaning that when gantry is mounted and squared, i just screw the nut to the nut plate and moved the gantry one side by hand. Screwed the ball screw mounts, then repeated at the other side. Then tightened. So no fiddling with alignment and so.


About the welding i also have not welded before. Played around a bit , watched some videos on YouTube and was good to go. Just remember- if arc or mig welding the most important thing is to keep the arc at the same distance and watch the pool and spread it, not think about quality, instead think about welding strong with good penetration. just zigzag to ensure penetration.

CharlieRam
09-09-2014, 02:11 AM
i also am wondering about that diagonals and at the same time big holes in the middle. I don't know the top you are planning on but generally i wouldn't have a hole in my table bigger than 300mm, otherwise you will need 50-70mm top if made from ply or similar. even alu top would benefit from such maximum distance.
I will add another cross beam, maybe 2 then if I have enough material, as I mentioned earlier the plan is to put 4" x 1" 3mm alu box section over the length of the bed and then 10mm alu plate on top of that drilled and tapped.



IMHO you are mistaken about the ball screw end mounts. Do yourself a favor and design it similar like i did them from 10mm plate and additional plates that screw to that perpendicular reinforced with ribs plate.
Or you could find your self in a scenario that you have to file shims or even worse, what you will do if the ball screw has to go inside direction?
I understand what you are saying but so long as the rail seating faces are parallel to the bearing block seating faces and the bearing blocks are machined correctly then I will only have to adjust the distance to the Z plate which I am hoping to adjust with the ballnut housing bracket, out of interest how accurate are the ballscrew end blocks from base to centre height? If the heights are out I can always grind them at work while no one is looking!
Cheers, Charlie

CharlieRam
09-09-2014, 02:40 PM
Does this bed design look better? It is still made using 1 off 80x40x4mm 7.5mm long and 2 off 50x50x3 7.5m long steel.

Boyan Silyavski
09-09-2014, 03:18 PM
I see it better.

I measured the ball screw mounts i use/chinese/ . They are 0.01mm precise.

CharlieRam
09-09-2014, 03:25 PM
Thanks for that, I guess that would be more than acurate enough considering the runout/bend of the ballscrew could be more than that.
Cheers, Charlie

CharlieRam
23-09-2014, 10:02 PM
Does this bed design look better? It is still made using 1 off 80x40x4mm 7.5mm long and 2 off 50x50x3 7.5m long steel.
I keep going back to my bed design and I'm wondering, for a novice welder (zero experience!) will I need to add adjust-ability into the X rail supports, I have allowed for 5mm thick epoxy but I am just a bit concerned about welding the frame only to find it is twisted or out of square?? If I were to make the X box section bolt on to the bed frame rather than welded would it be strong enough and would I be able to skim the 80x40 seating face acurately enough to bolt the rail directly without the need for epoxy.....I think what I am asking is 'how flat does the seating face need to be? less than 0,01 or is it more forgiving than that?
Also if I go the epoxy route I have read people say drill and tap after applying the epoxy, could I do that with a standard drill or would I need something like a magnetic drill press? I was thinking to drill and tap the holes and coat some bolts with molten wax and then fix them in place before pouring the epoxy, would that work or not?
Cheers, Charlie

IanS1
23-09-2014, 10:22 PM
You want to try to avoid welding directly to the X axis box section. You can weld a 10mm plate to the top of each upright along the X axis then bolt through that plate into the X axis box section.

CharlieRam
23-09-2014, 10:34 PM
This is what I had in mind, There will be aluminium blocks in each end of the X box section tapped to accept the the two bolts through the legs?

Boyan Silyavski
24-09-2014, 07:56 AM
Nothing will happen if you weld carefully, tack everything together, don't make stitches bigger than 5cm, use your brain to figure what to tack before so it would not twist and most of all be patient. It really takes a lot of time welding a CNC frame.
What you suggest is alternative but people go further this way and don't use epoxy at all / only at the shims/

Anyway, most of all you should care for your top 2 rails to be more or less in the same plane. On paper the epoxy to spread the force needs to be minimum 3mm thick, so basically that's your limit. You can pour more than 5mm if needed.

JAZZCNC
24-09-2014, 08:26 AM
My prefered way is to use adjustable top rails and shims as it's more foregiving and can be better tweaked. It's does take longer much longer than epoxy with lot of time needed to get perfect but when done thats it. Also if the machine frame releases any stresses overtime you can adjust this out if need be which you can't with epoxy.

I'll repeat for the million'th time but build in has much adjustment as possible and brace the hell out the frame and you'll have very very strong machine that's foregiving to those with limited means or engineering abilty. Silyavski as said everything regards welding except spread the heat around and don't weld in one spot for too long. Take breaks and it's a bit like eating an Elephant.? Lots Small bites.! . . . .. This goes thru out the build take it in small bites don't rush just to get it done or the machine will suffer for it.!

IanS1
24-09-2014, 09:01 AM
This is what I had in mind, There will be aluminium blocks in each end of the X box section tapped to accept the the two bolts through the legs?

As Jazz as pointed out, the more adjustability you have, the better. Cutting and fixing the ends of the X box section the way you have drawn could make the adjustability more restrictive. Also, bolting through the end uprights may cause the frame to warp as you tighten the bolts.

EddyCurrent
24-09-2014, 10:02 AM
Your frame is similar to mine, this is what I did;

http://www.mycncuk.com/threads/6565-Ready-Steady-Eddy?p=52425#post52425
But I also welded matching 10mm 'pads' onto the underside of the X box section, http://www.mycncuk.com/threads/6565-Ready-Steady-Eddy?p=54294#post54294
That was a mistake I think ! http://www.mycncuk.com/threads/6565-Ready-Steady-Eddy?p=54024#post54024
I always intended to use epoxy as well.

Instead of welding to the underside of the X box section, I would glue a piece of flat bar inside it using Gorilla Glue, similar to this ; http://www.mycncuk.com/threads/6565-Ready-Steady-Eddy?p=54981#post54981
because it increases the wall thickness of the box section allowing a secure fastening through the plates welded to the top of the legs.

CharlieRam
24-09-2014, 11:46 AM
I'll repeat for the million'th time but build in has much adjustment as possible

This is why I revisited the frame but what about the rail mounting surface, would it be accurate enough to skim the top face on a milling machine and bolt the rails directly to this or do you still recommend the epoxy and if I go the epoxy route would I be able to seal all the threaded holes by covering the screws in molten wax or will the epoxy melt the wax while setting?
Just to say, I am a competent machinist and I'm quite confident in my skills, it is the welding that I will struggle with but I'm sure it will come good!
Cheers, Charlie

JAZZCNC
24-09-2014, 12:35 PM
Yes skimming surface will be fine and all that's needed. Then just shim the rails onto same plane if needed.

Welding at this level is simple just practice on some scrap and you'll be fine. Where not welding oil rigs here so bit of pigeon shit is fine and it all cleans up with a grinder.

CharlieRam
24-09-2014, 04:36 PM
Cheers everyone, what about the ends of the X supports. Could there be an issue of strength where i have cut into the box section, I am hoping it wont matter so much at the end of the travel as the carriages will still actually be on full box section, only by about 25mm though. I could glue a 5mm steel plate under those areas.
One last thing for now, will 4mm thick steel be strong enough to tap through for bolting the rails?
Cheers, Charlie

Tinkerer
01-10-2014, 09:27 AM
Hi RouterCNC

I thought I would go to the effort and recognise your outstanding work on the stiffness calculator. It has removed guesswork on my part and/or countless days of research. Thank you. I had your v7, but see it has been improved with v8! Again many thanks.

Richard

CharlieRam
14-08-2015, 11:09 AM
Well, after a long break....well more finishing other jobs :-)
Design 14 is ready for your scrutiny, pretty much everything is designed to size apart from bolts. just working out a BOM at the minute to work out the costs. The bed is part welded and part bolted but I am wondering if I could bolt the whole lot and still keep a strong structure? what are your thoughts.
I have included the full sketchup model so you can have a good look if you want, all components can be ungrouped and moved along there respective axis so have fun!
Thanks, Lee

CharlieRam
24-08-2015, 11:22 AM
Hi guys, what is your opinion about swapping the angled box section for 5mm thick steel plate, will it significantly alter the strength, have a look at what I mean below. All corner braces would be the same as the white one if it is ok.
Also I am considering having the frame bolted together rather than welding other than the flanges that are welded to the upright pillars suspending the X axis, if it is all bolted I would be able to dismantle to make any mods or changes but in your opinion would it still be rigid enough.
I've just ordered my Rage 3 saw :-) and when I get paid in 4 days the steel will be ordered but it comes in at just under £200 and if I can swap some of the box for flat I could save about £40. every little helps!
Thanks, Charlie.

toomast
24-08-2015, 02:53 PM
I would not use steel flat-bar in there. I understand that it is easier to build it like that but I doubt you gain much with this design. In order for diagonals to work effectively other ends must be connected as well. So I would advise box section for diagonals + connect the other ends with box section too. For diagonals you can use smaller profile. If you want to keep adjustment option then you must weld the end-plates and use bolts.
I'm currently redesigning my machines frame - adding connections for the other end of the diagonals and making profile smaller but thicker.

Boyan Silyavski
24-08-2015, 03:20 PM
I would use no diagonals at all as the structure seems right to me. However i will use 10mm thick plate for the bolt on connections. That should do it

CharlieRam
24-08-2015, 03:29 PM
Thanks for the quick replies guys.

I would use no diagonals at all as the structure seems right to me. However i will use 10mm thick plate for the bolt on connections. That should do it
Hi Boyan, when you say no diagonals, you mean to remove all angled box sections? and then swap my 5mm plate for 10mm on the existing bolt plates, the reason I chose 5mm was because it would be easier to weld to the 4mm box section (I think!)
Cheers, Charlie

Boyan Silyavski
24-08-2015, 03:38 PM
Thanks for the quick replies guys.

Hi Boyan, when you say no diagonals, you mean to remove all angled box sections? and then swap my 5mm plate for 10mm on the existing bolt plates, the reason I chose 5mm was because it would be easier to weld to the 4mm box section (I think!)
Cheers, Charlie

Yes,
and if you do the small effort of designing and welding additional bottom plates where the threads will go, i am sure about that.

There is no problem welding 10mm plate to 4mm box section, on the contrary, the weld when properly done will make things stronger


Anyway, you could just buy 6m flat 10mm thick bar and cut it to many pieces with the Rage.

CharlieRam
26-08-2015, 10:58 PM
I have been looking at the X drive and have modeled up what I have in mind, I was originally thinking twin motors but I didn't want to tie up a 4th drive, so if I go for the following method would the belt length cause too much issue (I have worked out the belt length and the nearest standard length from Zapp is 1895mm) and also would a nema 23 do it or should I go upto a nema34. In the first image the belt is housed in a 50x25 3mm thich channel, in the second I have moved it up to show the belt run. This gives me about 2mm inside the box section in all directions clearance. Should I expect more belt sag or whip , I am hoping if they are tensioned OK then it will be sufficient but as I have no experience of using belt drives I have no Idea!
Cheers, Charlie

njhussey
26-08-2015, 11:08 PM
I've got a Nema 34 on my X axis, in theory a Nema 23 would do it but I wanted to be sure....

Clive S
26-08-2015, 11:12 PM
There is no problem using one motor I think most would use a nema34 in this case. You can buy the belts made to measure it might be an idea to have the belts lower down so as to be able to put long lengths of stock through the back etc.

CharlieRam
26-08-2015, 11:17 PM
Cheers, Just noticed your build seems to have a long belt on, Does it whip much on change of direction and whoa, there big pulleys, do they need to be that big? I was going for minimal?

CharlieRam
26-08-2015, 11:34 PM
Sorry, that last post was to njhussey, You posted to quick, I know I can get a belt long enough but I don't know if the flex/whip will cause issues such as catching the inside of the box section which I plan on using just because that is whats left from my cut plan :-) If theres a problem then I would rather rectify it now rather than buy stuff that won't work...I'm tight like that ;-)

Clive S
27-08-2015, 07:35 AM
The problem with big pulleys I am led to believe is the inertia that they have. I have no idea on how much the belt will sag but you can always add the belt cover when you have it up and running.
You will need to run a 70V power supply for the motors.

njhussey
27-08-2015, 08:17 AM
I'm running my Nema 34 on a 230V Kinco driver and at the moment it's running on 10 m/min rapids and very happy, had it on 15 m/min and was still happy but don't need that sort of speed. I got the 40 tooth pulleys as the Nema 34 has bags of torque and I wanted as much tooth engagement as possible...

I've not noticed any whip on change of direction...

Clive S
27-08-2015, 08:22 AM
Neil I thought you had used 230V but when I looked at your schematic I saw three drives connected to the PS did you originally go with nema 23 all round?

njhussey
27-08-2015, 08:26 AM
Neil I thought you had used 230V but when I looked at your schematic I saw three drives connected to the PS did you originally go with nema 23 all round?
I've got an AM882 driver for a 4th axis as well now but did originally plan to use a Nema 23 on all axis as the calculator showed I'd be able to use it on the X axis but I decided to play it safe and go up a size.

Clive S
27-08-2015, 08:28 AM
I've got an AM882 driver for a 4th axis as well now but did originally plan to use a Nema 23 on all axis as the calculator showed I'd be able to use it on the X axis but I decided to play it safe and go up a size.
Ah! that fooled me :beer:

njhussey
27-08-2015, 08:43 AM
15966

On the schematic it only showed the two AC wires that were going to the driver, don't think I even put a representative box on it....:surprise:

Clive S
27-08-2015, 08:54 AM
http://www.mycncuk.com/attachment.php?attachmentid=15966&stc=1

On the schematic it only showed the two AC wires that were going to the driver, don't think I even put a representative box on it....:surprise:I looked here http://www.mycncuk.com/attachment.php?attachmentid=15031&d=1427797357&thumb=1 (http://www.mycncuk.com/attachment.php?attachmentid=15031&d=1427797357)but didn't notice the 230V drive. That will teach me to assume. http://madmodder.net/Smileys/default/BangHead.gif ..Clive

CharlieRam
28-08-2015, 12:01 AM
I have been looking at the nema 34's and I am confused about the specs..
They all seem to quote a recommended voltage of about 2v, whats that all about? Would one nema 23 just not be able to move the mass because the 34's are quite a bit larger and wont fit in the location I have put it, which means putting 2 nema 23's one on each ballscrew which then also means a controller which supports slaved drives and controllers with error detection which means £££ ! I am trying to sell this to the better half as a bit of additional income but when I mention a couple of hundred pounds extra on top of my ever increasing budget she doesnt seem very impressed, I don't know why:stupid:

njhussey
28-08-2015, 10:26 AM
Charlie, what's the weight of your gantry complete with the spindle? If you put that weight into the motor calculator spreadsheet you'll be able to see if one Nema 23 will do it. On my gantry it was going to be only just ok (I've got more plate in mine than you have as I believe from the drawings you're using alu box sectio to mount your rails to?) so I went larger to be on the safe side. If you're borderline all it will mean is that you won't get the higher speeds of velocity and acceleration.

CharlieRam
28-08-2015, 11:35 AM
Well I have attempted to work it all out and this is what I came up with?

Aluminium on gantry 31kg
800mm rails+blocks 5.8kg
400mm rails+blocks 3.6kg
4 blocks on x axis 1.6kg
Z ballscrew+mounts 2.5kg
Y Ballscrew+mounts 3kg
x axis ballnuts 1kg
2 nema23 motors 3.6kg
CapScrews? 2Kg

Total weight 54.1Kg

Does that sound about right? have I missed anything. I suppose I need to look at the calculator now.

Cheers charlie

njhussey
28-08-2015, 11:42 AM
How about your spindle? You'll also need a bit extra for cable tray, cables water tubes etc....

CharlieRam
28-08-2015, 11:47 AM
How about your spindle? You'll also need a bit extra for cable tray, cables water tubes etc....

Doh! I completely forgot about the spindle, Won't do much without one will I :thumsup:

CharlieRam
28-08-2015, 11:52 AM
Just had a look at spindle weight and it looks like 5.6kg, maybe another 1kg for cable and pipe so total weight comes in at 60.7kg

Neale
28-08-2015, 05:44 PM
Quick answer to your question about "2 volt motors". Ignore motor voltage ratings. For all practical purposes, they are irrelevant. The control electronics are driving short pulses through the motor windings and include some clever controls on motor current, which is the important bit. The motors work using magnetic fields; the higher the current the stronger the field and the more torque you get out of the motor. However, the motor windings are coils of wire which have inductance. In this situation inductance is a bad thing because it slows down the rate of increase in current at the start of each pulse so you lose power. To get round this, you drive the coils with many times their rated voltage - maybe 60-70V for a nominal 2-3V motor - so the current builds more quickly. Then the current limiter in the driver reduces the applied voltage automatically during the pulse so the motor isn't over-driven. This all happens like magic and all you need to know about is the current limit setting in the driver module which should match the motor.

Clive S
28-08-2015, 05:54 PM
Neale Very good explanation much better than I could have done it:encouragement: ..Clive

CharlieRam
01-09-2015, 12:19 AM
Well, I've gone and done it, no turning back now....

Chester champion 20v milling machine ordered
steel for frame ordered
aluminium for gantry/frame ordered
welder borrowed
wife prepped

Bit lighter in the plastic pocket now but feel like it's something I need to do otherwise I will never get started!

I will get the frame and gantry started before I order the ballscrews and rails, I wont be making any fixings for them until I have them in hand just in case and once they are done I will then decide on the motors,drives and controller at which point I will need a lot of help :-)

CharlieRam
20-09-2015, 09:28 PM
Here goes, my steel and aluminium have arrived. My mill is installed and I've had a play with my evolution saw... It's bloody loud when cutting steel but I'm really impressed with it. I feel like I need to make a new build log and close this thread off now? Just one question though, how do you lot measure your large beams (eg. 1350mm) after machining, do you just rely on your machines açcuracy, I've only got a tape measure!
I was thinking about getting a 3 axis dro for my machine but connecting the 3rd longest scale to some round rail to make a large height gauge. What do you think?
Anyway here's a couple of pics and I'll see you all in my build log when I post it :-)http://images.tapatalk-cdn.com/15/09/20/72428b188cfeac8abaeac47a557c43bc.jpghttp://images.tapatalk-cdn.com/15/09/20/49a36c1233b41bc58c74c50b377a8ae3.jpghttp://images.tapatalk-cdn.com/15/09/20/f920585b821d5132c5ce80be8a3c226f.jpg

Tenson
21-09-2015, 12:23 PM
Tape measure is pretty accurate, more than you might imagine ;)

Very clean, where is all the mess from cutting!?

CharlieRam
21-09-2015, 10:05 PM
Not done much cutting yet, just facing the beams so they are square and using my tape measure for measuring ;-)

CharlieRam
11-10-2015, 10:58 PM
Spent about 3 hours today learning to weld...Think I need another 3 months and I might get somewhere! I kept getting the rod stuck , I managed to get it arc'ing probably 2 or 3 times and once it was arc'ing I could get it going again until I changed the rod and then it was back to square one :-( , am I using too low an amp setting? I am using 2.5mm rods and I tried the welders recommended setting of 80amps but the only time I got it arcing was at about 110amps. Is that too high or should I go higher still.
Better still, any welders in the Derby area want to help me out who needs the use of a mini mill :-)
Cheers, Charlie

mekanik
12-10-2015, 10:16 AM
Hi Charlie
I don't do a lot of stick welding as i have TIG but i do use it for rough jobs, you should be OK with the recommended Amps, what usually happens as you have found is the rod sticking to the job then you can't pull it off and it starts to get red hot so you have to release it from the holder. sometimes you can drag the rod across the job to initiate the arc but i prefer to peck it until it starts the arc.
if you get a sticky one that wont start just file a notch through the flux a bit further up and break the end off to expose the electrode and try again. you will get the hang of it.
Regards
Mike

CharlieRam
12-10-2015, 10:29 AM
Thanks for the reply, I have watched tons of YouTube videos so should be an expert by now :whistle:, I have tried the drag (strike a match) and tapping method but before I even manage an arc the rod seems to stick, maybe its in my technique, I will try again.
Cheers, Charlie

Tenson
12-10-2015, 12:16 PM
I'm not a welder but if you are having trouble getting it to arc, have you made sure the material is clean and a good conducive surface is exposed?

mekanik
12-10-2015, 01:43 PM
Charlie
Try practicing without the set set on, what you appear to be doing is not pulling the rod away to allow an arc to form, so tap the workpiece and pull the rod away about 15mm with the power on the arc should initiate, then lower the rod to get a stable arc.
re cutting to length, tape rule should be fine but i dont like the loose bit on the end so always measure from the 100mm mark and add 100mm to your required length, i clamp the rule with a rubber faced clamp.
Good luck
Mike

komatias
12-10-2015, 04:07 PM
80 amps seems ok from my experience (a few 10s of 2.5mm and another so many 3.2mm). If between rods you cannot get it to arc, try breaking the flux around the electrode by hand. Careful, it is hot.

It really makes a difference when you have very clean metal both on the hot side as well as where you apply your grounding clamp. Also try to minimise the distance between the two.

Regards

George

Blackrat
12-10-2015, 07:25 PM
how old are your rods ?

JAZZCNC
12-10-2015, 07:39 PM
Warm the rods before using put them in oven or on radiator over night. Damp rods make a big difference has do cheap rods.!! . . . Damp Rods and cheap quality you'll always struggle if not experienced.

Practice on some scrap material of the same type your trying to weld.! Then When welding have piece of scrap at the side and strike up on this first to heat the rod.

CharlieRam
12-10-2015, 07:53 PM
I don't know how old the rods are cos my mate who lent me the welder gave me 3 full packs of different sized rods. I had another play today and I was able to strike the arc more consistently so maybe just a bit more practice needed.
I will try warming some rods in the oven and yeah I am practising on off cuts ATM. Wouldn't dare try it on my frame yet!
Cheers Charlie

njhussey
12-10-2015, 09:00 PM
It's definitely worth getting some nice new rods, they're not that expensive and make all the difference! I had some old rods and was struggling to strike an arc and I got fed up and bought a bix of new ones. You'll be amazed at the difference...now I'm not a good welder, in fact I'm pretty rubbish (bloody love my grinder!!!!!) but decent rods are a must :)

toomast
18-10-2015, 05:28 AM
One oldschool trick is to strike the electrode and let it stick for a few seconds until it starts to "sweat". Then use it as normal. I would only use this method when emergency and out of good try electrodes...

CharlieRam
22-10-2015, 12:42 PM
Just a quickie to show my progress (Or lack of it!) My welding is improving now, still not great but better than before.
It seems I was upping the ampage to compensate for my complete inability to weld but now I have the hang of it the amps are set right for the rod size and the welds are starting to look like real welds [emoji3]
Cheers, Charlie

http://images.tapatalk-cdn.com/15/10/22/59e1048c2daa58cbd7ac0f50dead5f3f.jpghttp://images.tapatalk-cdn.com/15/10/22/080267bbb3b3ebdf54562112d6bb08cc.jpg

CharlieRam
28-10-2015, 09:20 PM
http://images.tapatalk-cdn.com/15/10/28/fbb335b62af800079899538e5df54369.jpg
Getting there, welding still looks like pigeon sh*t but at least it looks like it will hold together now.
Cheers, Charlie

Sent from my XT1072 using Tapatalk

CharlieRam
12-11-2015, 02:01 PM
This welding lark is doing my head in! 4 weeks on and all I seem to do is weld, break of the slag and clean only to discover it welds on either the plate or box section but very rarely both together, my box section is getting thinner and thinner from grinding back :-( I am now also at the mercy of the weather so got knows when the frame will be finished but I need to make sure my welding's better before I start on the top rails. I keep watching youtube, playing about with different rods, amps and angles, bought a new visor with adjustable darkness so I can actually see what I'm doing but I think I just can't weld!
Cheers, Charlie

mekanik
12-11-2015, 04:27 PM
Stick @ it Charlie.
One of the reasons i opted for a TIG setup is that you can see exactly whats going on and you know the two bits are fused.
Frame looks good M8
Regards
Mike

CharlieRam
12-11-2015, 06:56 PM
Cheers, it's just so frustrating going over the same thing again, thinking you've cracked it only to discover its as bad as the last one!

Sent from my XT1072 using Tapatalk

njhussey
12-11-2015, 07:15 PM
Charlie, my welding is the same as yours. I think I've cracked it and then lay a weld that's just attached to one piece...just keep at it. Law of averages means that although you might get through lots of grinding discs you'll get there eventually by having more goid welds than bad ones!!

mekanik
12-11-2015, 09:01 PM
I think it would be prudent to do some more test welds, try turning up the amps a bit and try to hold a short arc.
Good luck

CharlieRam
12-11-2015, 09:26 PM
I would but I ran out of scrap bits of metal ;-)

Sent from my XT1072 using Tapatalk

CharlieRam
18-01-2016, 08:16 PM
Been a bit busy with other things lately but had time to fit my Christmas present to my Chester champion v20 mill. My good wife bought me a dro kit, saves me counting the turns when drilling [emoji55] http://uploads.tapatalk-cdn.com/20160118/69384d0419f21b77e547a3f5143443a9.jpghttp://uploads.tapatalk-cdn.com/20160118/f31bca4df8840db9f36348c0b65a33aa.jpg

Had a little play with it but still managed to drill some holes in the wrong position [emoji16] although they were correct to my drawing, I obviously didn't position them correctly in sketchup and I just blindly followed all the positions. It's not a biggy though as it won't be seen and I'll put it down to weight reduction [emoji106] . spot the deliberate mistake http://uploads.tapatalk-cdn.com/20160118/b43ac17121b3d0b2fe11bfc5c789ad07.jpg

Also I am thinking of buying these castors for my machine

http://www.ebay.co.uk/itm/331315782016

they are rated at 110kg each which should be more than capable of holding the weight of my machine which will come to about 200kg without any workpiece. They are total lock castors which means the wheels and swivels lock and they have rubber tyres.

I'm wondering if anyone else uses their machine on castors and if they have any problems like the machine skipping around?
Cheers, Charlie

Sent from my XT1072 using Tapatalk

kingcreaky
18-01-2016, 08:36 PM
Loving the mill :D

perhaps once you have witnessed the machine dancing about without castors, you will be in a better position to decide whether you want them :?

CharlieRam
18-01-2016, 08:47 PM
Haha, yes I am expecting it to dance whether it's on castors or legs but I am thinking if I have it bolted or strapped to the floor it won't move. I am wondering if having it sat permanently on castors is a bad idea? I like the idea of being able to easily move the machine when needed and it also has the added benefit of raising the bed by about 130mm. It seems a bit low now I've built the frame.
Cheers, Charlie

Sent from my XT1072 using Tapatalk

CharlieRam
28-01-2016, 06:31 PM
http://uploads.tapatalk-cdn.com/20160128/06f4b672a623eecc6030946f1a8c2933.jpg
Can anyone tell me if its safe to take these carriage's off the rails to allow access to the bolts when I fix them to my machine, they all came on the rails and I don't want to take them off and find loads of ball bearings falling out?

Sent from my XT1072 using Tapatalk

Neale
28-01-2016, 06:39 PM
No, it isn't safe. DAMHIKTIJKOK.

My carriages came with little plastic slides that fill the hole as you slide the carriage off the rail - not sure if you could use a flat piece of plastic about the right size?

Lee Roberts
28-01-2016, 06:40 PM
No no, need to slide them off onto something the same size/shape as the rail, some expanded polystyrene works if your careful.

.Me

CharlieRam
28-01-2016, 06:44 PM
Bugger, I was afraid of that, gonna have to try and find something the same shape then to slide them onto? Going to have to try and make a mock rail then, would wood be OK?

Sent from my XT1072 using Tapatalk

CharlieRam
28-01-2016, 06:52 PM
No, it isn't safe. DAMHIKTIJKOK.

My carriages came with little plastic slides that fill the hole as you slide the carriage off the rail - not sure if you could use a flat piece of plastic about the right size?
Just had to google that to find out what you meant!!

JAZZCNC
28-01-2016, 08:25 PM
Flat piece of plastic or wood about 3mm thick same width as slot ball fit into with tapered edges will work best. Foam and sponge can let the balls fall out if rails arnt perfectly lined up and push on them wrong.

To be honest thou If those are TBI bearings, which they look like then I think they are held in with plastic cage and don't fall out. The tricky part is putting them back on because you can easily damage the plaistc cage if not careful. . . . Better to be safe than sorry so make.!

CharlieRam
03-02-2016, 08:34 PM
The branding on the bearings is PDF, I tried searching for them but couldn't find them online, I got them off Chai before everyone switched to fred! not to sure about the rails, a bit bowed and terrible looking grinding bounce along the profiled angles but they seem smooth enough when moving by hand with a bit of pressure on them. time will tell I suppose.
I'm having a right mare trying to machine the faces flat for mounting the rails, it seems I needed a bigger mill because even with the gibstrips adjusted the bed sags with the weight when moving to the extremes of the slideways causing a bowed face so I'm going to clamp it upright and mill with an end mill instead of the flycutter I was using. what this means though is I am more than likely going to have to Epoxy my steel rails cause they are even longer and heavier than the aluminium gantry.

CharlieRam
18-02-2016, 11:40 AM
Just put the bearings on my ballscrew for the gantry and gave it a spin, it's a bit bent, the runout on the ends near the bearings is about 0.001" but in the middle it's over 0.020", my DTI doesnt read any more than that but I estimate it to be about 0.030"/0,75mm. Now I can attempt to straighten it on my mill but before I do, What would be considered as a reasonable amount of runout please?
Cheers, Charlie

JAZZCNC
18-02-2016, 01:40 PM
Just put the bearings on my ballscrew for the gantry and gave it a spin, it's a bit bent, the runout on the ends near the bearings is about 0.001" but in the middle it's over 0.020", my DTI doesnt read any more than that but I estimate it to be about 0.030"/0,75mm. Now I can attempt to straighten it on my mill but before I do, What would be considered as a reasonable amount of runout please?
Cheers, Charlie

Obviously the ideal is zero or near but I've seen worse work perfectly fine. I'd just fit it before doing anything because I think you'll find the runout won't be noticable when attched to ballnut mount. If you have vibration then it's an easy thing to remove and straighten.

CharlieRam
18-02-2016, 01:51 PM
Cheers for the info, I will fit it as is for now then.
Charlie

CharlieRam
22-02-2016, 10:37 AM
Hi, I have a few questions about the BK12 bearing supports, I've tried two of the supplied ones so far and the both exhibit end float, so after searching the forums I have tried placing the bearings back to back, packed with grease and reassembled but I think I need to shim them, the problem is how do I know what to shim, the ID or OD and where can I buy the shims from?
Also when the ballscrew is pushed fully into the bearings, it doesnt spin freely even with the nut slackened off, I assume I should be able to give the ballscrew a spin and the momentum should keep it spinning for a while, It may be the seal because it occasionally spins with the ballscrew but I have tried pushing it in a bit and pushing it out but it makes no difference? Any advice or help greatly appreciated.
Thanks, Charlie

Edit just checking this is Back to Back?17676

njhussey
22-02-2016, 02:21 PM
Hi Charlie, the pic shows them back to back, I've got mine shimmed on the OD (as you want the tightening to pull the inner races together and load the bearings slightly) and cut the shims out of ali cans (good source of 0.1mm thick shim material as well as providing refreshment!) with some sharp scissors for the OD and a stanley knife for the ID. Think I used 2 or 3 shims per BK support but can't remember now.

CharlieRam
22-02-2016, 08:48 PM
Best get some more beer in then! What about the rubber seal, should it be spinning with the ballscrew?
Cheers. Charlie

JAZZCNC
22-02-2016, 09:21 PM
Best get some more beer in then! What about the rubber seal, should it be spinning with the ballscrew?
Cheers. Charlie

No it shouldn't be touching the seal.! . . . Sure you haven't lost the little spacer.?

Some times they can be different lengths so check this. I've also known them be too short has well thou so it may mean spacer or making another.

CharlieRam
22-02-2016, 10:16 PM
The spacer is the thin tube that fits in the rubber seal upto the bearing ID right? if so then they yes they are there, I will check if both sides are the same length and if not I will swap them over.

njhussey
22-02-2016, 11:28 PM
They're different lengths, well mine were!

Boyan Silyavski
23-02-2016, 12:36 PM
Are all pieces there assembled like that?

17688


So if the whole bearings are moving in the housing, then shim the OD of the bearings. If only the ID of the bearings are moving, then shim only the ID. When shimming, dont shim between them, but outside in both cases.

If not freely rotating, then something is not right. It must be something simple, so just check again

CharlieRam
23-02-2016, 03:29 PM
It's all there apart from the lock washer, do I need one?

CharlieRam
24-02-2016, 12:01 PM
https://youtu.be/9jVThNfMAM4Heres a little video of what I mean, if the screw is pushed upto the sleeve, the seal starts to spin. I'm wondering if the spacer O/D is catching on the seal and when it is butted upto the bearing face it is dragging it round? Also I'm still not sure how freely the screw should move, I was expecting it to spin a little like a roller skate bearing, it seems to have resistence even without tightening the nut. The spacers are different lengths but if I put them the other way round the outer one would be too short and be inside of the seal, the way they are now both sides protrude from the seals.
Any help and advice greatly appreciated.
Cheers, Charlie

njhussey
24-02-2016, 12:08 PM
Here's a pic of mine, the spacer goes beyond the seal to keep the face of the machined shoulder away from the seal.

http://uploads.tapatalk-cdn.com/20160224/100a05c208fca818834c3211406e1392.jpg

CharlieRam
20-04-2016, 08:17 PM
It's been a while so heres a little update.. been working on the Z axis and also repairing my mill in the meantime as I stripped the plastic gear on my Chester champion.
18249
But it's not moving very freely, I have clocked the rails up within 0,01 and put it all together including the ballnut and tried to push it up the rails, I could just about move it but it didn't feel very nice, I took the plate off and greased the carriages, and tried the rails on there own. one felt lovely and smooth but the other felt notchy on one of the carriages. So I carefully removed the rail and it appears as though I have a ball bearing missing!
18250
Would this cause a notchy/stiff feel in the carriage or have I got other problems? I measured one of the ball bearings and it was 3.98mm so am I right in assuming 4mm. This is the first time the rail has been off so it must of been missing when I got the rails and if it hadn't been for the notchy feel I wouldn't of taken it off so please no telling me off for removing it :-P

Cheers, Charlie

mekanik
20-04-2016, 08:57 PM
Hi Charlie
When you get the carriage cleaned and running smooth, bolt the rails to your Z plate with the carriages installed but not bolted to matting face, offer the carriage/rail assembly up to your other plate and check the matting face with feelers to see if both plates are flat, one or both of the plates might be twisted or something.
Regards
Mike

CharlieRam
20-04-2016, 09:16 PM
I've got to get the carriage running smooth first, I tried both carriages on each rail, one of the rails is perfect but on the other rail I have one notchy carriage, that is when i discovered what looks like a ball bearing missing, just wondering if anyone else has had a problem, I can buy some 4mm ball bearings and see if it makes a difference, it definitely doesn't feel right though.
PS. I did remove the rails from the Z axis to check I wasn't twisting it.

Lee Roberts
20-04-2016, 09:30 PM
Could do with the exact size ball mate, shouldn't really round it to 4 mil like that.

What you using to measure it?

I'll have a look in a mo as I've got loads of different size ball bearings, can send you some if you want.

Pop a ball out of a good unit and use it to check the dodgy one, let us know :thumsup:

.Me

CharlieRam
20-04-2016, 09:53 PM
I used a mic, but only a quick check and I may of been a bit over on the pressure, I was more bothered about dropping it in the swarf! I will measure a good one tommorow and get back to you, cheers. Do you think having one ball missing could cause the notchy tight fit? I'm thinking about removing all the balls and giving it a good clean incase the missing ball is actually in bits causing the notchy feel. Good idea or not? It doesn't look too hard, just a bit time consuming.

Lee Roberts
21-04-2016, 12:27 AM
I used a mic, but only a quick check and I may of been a bit over on the pressure, I was more bothered about dropping it in the swarf! I will measure a good one tommorow and get back to you, cheers. Do you think having one ball missing could cause the notchy tight fit? I'm thinking about removing all the balls and giving it a good clean incase the missing ball is actually in bits causing the notchy feel. Good idea or not? It doesn't look too hard, just a bit time consuming.
OK nps.

Well yeah I would seems silly not to at this stage, like you say not difficult just a time thing, may as well do it now and rule it out then revisit.

I doubt it's a ball gone to bits in there, more likely to be something else got in, check the returns and any paths the balls take for damage, lumps and bumps things like that.

I just rebuilt two ball nuts for someone and on one of the nuts, a plastic return was just a little bit snug as the balls passed through it, the symptoms where a slight judder/nock as the nut was spinning on the screw.

If you know what brand/make and model we may be able to look up the right size ball.

.Me

CharlieRam
21-04-2016, 06:52 PM
So I stripped the carriage, 119 ball bearings, measured quite a few of them and they were 3,975-3,988 ish so my measurement last night was good, still notchy :-(

Would the lack of one ball really cause this issue? degreased and checked all ball tracks, checked the end plastic things by pushing the balls back and forth and they seem ok? Could the plastic cage thing be chafing?

Just out of interest I got some digital kitchen scales on the end of each rail and pushed on it until the rails started to move, the good one started to move at about 400g of pressure, the notchy one was just over 1000g, for info the rails are 375mm long.

BTW, the brand is PDF and model is DFH20A

sinnsvak
22-04-2016, 12:25 PM
I also have a set of 600mm PDF 20mm profile rails, which dont run smooth at all. I will change them out with hiwin down the road when I get some leftover money to do so. For now Im gonna keep it as it is until it proves to be a huge problem.

Lee Roberts
22-04-2016, 02:28 PM
So I stripped the carriage, 119 ball bearings, measured quite a few of them and they were 3,975-3,988 ish so my measurement last night was good, still notchy :-(

I would think they are to the closest standard size of 5/32in then, your in luck as well because I've got some that size, PM me if you want me to send you some, call it the postage cost...

Lee

CharlieRam
22-04-2016, 05:57 PM
I also have a set of 600mm PDF 20mm profile rails, which dont run smooth at all. I will change them out with hiwin down the road when I get some leftover money to do so. For now Im gonna keep it as it is until it proves to be a huge problem.

Lee Roberts is sending me some ball bearings, I'll see if it makes a difference and if not I will fettle the carriage a little......Now wheres that bastard file ;-)

sinnsvak
22-04-2016, 06:02 PM
Good Luck! It may be, and I sincerely hope so, that the smoothness will show up after a couple of hours use.

CharlieRam
29-04-2016, 02:31 PM
Well that's been a few days of discovery I won't forget in a hurry!

I stripped the carriage again, gave it a good clean and scotchbrite on all ports and ball ways, reassembled the carriage temporarily, put it back on the rail and started to slide it up and down to check the tightness and then....the end came off and 120 balls all over the floor! F$%k, I found 118 of them and still had 2 spare from Lee luckily.

Oh yeah, I also decided to check the other carriages now I'm confident the balls wont go flying if I remove them :stupid: a couple of the others seem to have one ball missing too!

Cleaned it all again and secured it properly this time but it still felt tight, that is when I noticed the carriages looked slightly different on the exterior, so I checked the serial numbers again, both are DFH20A but the nice fitting ones have S01411040 and the tight one has S01207841. Does anyone know if any of these numbers signify the preload, I'm thinking I may have a higher preload carriage or is it just a batch number and one was made at a different time with not such a good QC?

More Importantly, will it affect the build having a mis matched carriage?

Cheers, Charlie

Lee Roberts
03-05-2016, 05:16 PM
Hi Lee,


so I checked the serial numbers again, both are DFH20A but the nice fitting ones have S01411040 and the tight one has S01207841. Does anyone know if any of these numbers signify the preload, I'm thinking I may have a higher preload carriage or is it just a batch number and one was made at a different time with not such a good QC?

Cant help there sorry, what you could do is mic the ball's and see if they are diffrent, this may give you the anwser.


More Importantly, will it affect the build having a mis matched carriage?

I can’t see it being a problem, so would just go with it, others may know better but I can’t think what problems it may introduce, ultimately if it is a preload difference then its unbalanced but would suggest it’s going to be such a small amount, just leaving you with the least amount of preload as your best number, so again not a problem.

.Me

CharlieRam
03-05-2016, 10:04 PM
Hi Lee,

Cant help there sorry, what you could do is mic the ball's and see if they are diffrent, this may give you the anwser.

.Me
Is that how the preload is set then? with slightly larger ball's?

Lee Roberts
03-05-2016, 10:35 PM
Is that how the preload is set then? with slightly larger ball's?

Hiya,

Pretty much yes, if you use slightly bigger ball bearings than the distance between the carriages and rail.

The ball bearing size (relative) determines the amount of preload achieved. From what I've read, the most common amounts of preload used for linear guides are 8, 5 and 2 percent of their load rating (dynamic).

For ballscrews and nuts you can do the same thing with the ball sizing, use an adjustable nut or use two nuts.

.Me

CharlieRam
16-08-2016, 03:45 PM
Well.....I've been a bit quiet on here and for good reason, I found out my good wife was having an affair!! So dealing with a lot of shit at the minute, mainly custody of the kids and making sure I still have a family home and some cash left at the end of it. Just had my Decree nisi date for the 1st September so all being well and if we can come to a fair agreement on asset splitting (Fair to me would be she got F all but that ain't gonna happen) Hopefully I will be divorced middle of November, What a waste of 22 years! but onward and upward and hopefully I will be in the mood to start/finish my machine soon. Think I need a hobby to get me out the house and meet some new people.
Take care and if you feel like lifes getting you down....Just think about me and how it could be worse and have a good chuckle :) I know it's not quite life or death but sometimes it feels like it!

JAZZCNC
16-08-2016, 07:27 PM
Charlie I've got the T-shirt been there done that in exactly the same circumstances, actually was with my best mate so possible worse if you didn't know the Twat and let me tell you buddy it's the best thing that happened to me.!

You'll soon learn Money and assets mean very little in grand scheme. The kids will love you no matter what and even if young they are not stupid they know who's gulity so don't worry about them.

Stings like bastard at first and if you can get thru the Dark nights then after while you'll get your head around the fact that your FREE.!! . . . .Then it's Charlie Time. .:yahoo:

Keep chin up mate it does get better.:beer:

CharlieRam
16-08-2016, 09:06 PM
Well at least I didn't know the bloke but she did, she worked with him for six years! but the affair "only" started last August. It's not so much the affair but her attitude since I found out. She is trying to prevent me seeing the kids at every opportunity she can even though I was their sole carer for the first 2 months. Being a total be itch like I was the one who did wrong:grey: won't talk to me, Text only or "speak to your solicitor" She's gonna be in for a shock though because I offered her £40000 for a clean break and her solicitor said she'd get a lot more (without knowing any financial details) so she refused but it seems she may be entitled to less than that now and because she went straight to a solicitor she will end up with even less. Here's hoping.

toomast
24-08-2016, 11:42 AM
Hooray for single life!
Im free since yesterday...

JAZZCNC
24-08-2016, 01:20 PM
Hooray for single life!
Im free since yesterday...

Ah ah another one in the "Free to do what ever HE likes, with who ever HE likes club.!! . . . . Wise man once told me when fall off bike get straight back on but learn what caused the fall and don't make same mistake.

Same with Women.! Go out straight away get another BETTER model but learn from your mistake. Yes even if they did the cheating you had some blame.!!. . . Find what and change.!

The new improved you with better model stings the EX Bitch like nothing you can imagine.. . .Picture on my Ex wife face when I turned up for kids with New Car and prettier Passenger was priceless.!. . . . couldn't have hurt her more if I'd smacked at back of head with 3x2.!! . . . In all honesty Didn't make me feel good seeing her pain but did have small feeling of satisfaction in sense of "Aint Karma Bitch"

Good luck Lads the stinging soon goes away and then it's Happy days.!! . .:cheerful:

CharlieRam
24-08-2016, 07:17 PM
Same with Women.! Go out straight away get another BETTER model but learn from your mistake. Yes even if they did the cheating you had some blame.!!. . . Find what and change.!


I don't really agree with that Dean....If I was that bad or did enough for her to want to leave me then she should of done just that, not line up the next sucker while stringing me along and using me to get everything she wanted! It is just selfish and disrespectful, I could tell you some stuff about my soon to be ex that would make even your blood boil.

JAZZCNC
24-08-2016, 08:48 PM
I could tell you some stuff about my soon to be ex that would make even your blood boil.

Nah wouldn't because from that fateful day only Guiness corse's thru these vains and that's chilled to 7DegC at all times. . .Lol