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Well here goes... Aluminium frame router design
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
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Re: Well here goes... Aluminium frame router build
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
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Re: Well here goes... Aluminium frame router build
Gantry looks to high and the X looks to wide.
.Me
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Re: Well here goes... Aluminium frame router build
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
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Re: Well here goes... Aluminium frame router build
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
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Re: Well here goes... Aluminium frame router build
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.?
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Re: Well here goes... Aluminium frame router build
Quote:
Originally Posted by
JAZZCNC
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?
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Re: Well here goes... Aluminium frame router build
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.
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Re: Well here goes... Aluminium frame router build
Quote:
Originally Posted by
JAZZCNC
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
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Re: Well here goes... Aluminium frame router build
Quote:
Originally Posted by
JAZZCNC
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.
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Re: Well here goes... Aluminium frame router build
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.
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Re: Well here goes... Aluminium frame router build
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
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Re: Well here goes... Aluminium frame router build
Quote:
Originally Posted by
CharlieRam
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.
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Re: Well here goes... Aluminium frame router build
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
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Re: Well here goes... Aluminium frame router build
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-...aw-240v/60839#
Its £100 but says it will cut steel, ally, wood and whatever.
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Re: Well here goes... Aluminium frame router build
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!
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Re: Well here goes... Aluminium frame router build
Quote:
Originally Posted by
CharlieRam
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.
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Re: Well here goes... Aluminium frame router build
Quote:
Originally Posted by
JAZZCNC
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!
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Re: Well here goes... Aluminium frame router build
Quote:
Originally Posted by
JAZZCNC
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
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Re: Well here goes... Aluminium frame router build
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.
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Re: Well here goes... Aluminium frame router build
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!
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Re: Well here goes... Aluminium frame router build
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.
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Re: Well here goes... Aluminium frame router build
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?
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Re: Well here goes... Aluminium frame router build
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.
Attachment 12912
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Re: Well here goes... Aluminium frame router build
Quote:
Originally Posted by
routercnc
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.
Attachment 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
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Re: Well here goes... Aluminium frame router build
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
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Re: Well here goes... Aluminium frame router build
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
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Re: Well here goes... Aluminium frame router build
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?
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Re: Well here goes... Aluminium frame router build
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?
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Re: Well here goes... Aluminium frame router build
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.
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Re: Well here goes... Aluminium frame router build
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
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Re: Well here goes... Aluminium frame router build
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.
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Re: Well here goes... Aluminium frame router build
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.
Attachment 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.
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Re: Well here goes... Aluminium frame router design
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
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Re: Well here goes... Aluminium frame router design
Quote:
Originally Posted by
CharlieRam
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
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Re: Well here goes... Aluminium frame router design
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
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Re: Well here goes... Aluminium frame router design
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? :-)
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Re: Well here goes... Aluminium frame router design
Quote:
Originally Posted by
CharlieRam
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 post #109 and how looks finished from 12mm steel plate a bit up at the same page
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Re: Well here goes... Aluminium frame router design
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
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Re: Well here goes... Aluminium frame router design
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.