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deannos
22-01-2012, 08:44 PM
Hopefully this will work. I hoping to have the Y axis 1500mm long and the x 850mm, this will help with the space i have available and will make it easy with placing the work material. i have 16mm rails,16mm screw on the x. 20mm screw and 25mm rails on the Y axis and i was thinking 16mm screw and 16mm rails on the x axis. This will sit on a steel box section frame. Have i got it right or wrong:confused:. Also going to use belts and pulleys, that's 45x 45 ali profile and 20mm ali plate as well

routercnc
22-01-2012, 10:07 PM
Hi Deanos,

Looks like a 'landscape' format machine with such a long Y axis gantry. 1500mm is quite a long span for a pair of 45mm profile sections. You could double the (torsional) stiffness if you go for 'portrait' format and have an 850mm gantry, although you do mention that you want to make it easy to load material.

If you want to continue with this style then here's Joe's cnc in case you haven't seen it, which is very popular:
http://www.joescnc.com/themachines-hybrid.php

Any thoughts on how you will attach the X axis drive system (pair of leadscrews I assume) to the gantry sides?

deannos
22-01-2012, 11:18 PM
yes it will be a pair of leadscrews on the x axis, not sue on how to attach them yet.

JAZZCNC
23-01-2012, 12:48 AM
Hi Dean,

There's pro's and cons to both portrait and landscape designs. Landscape is good for reasons like only having one long screw on Y axis rather than 2 long screws on X axis which is a problem with large format machines, space saving and easy loading are just a bonus IMO.
The down side is that you need to really beef up the gantry and your choice of 45mm profile fastened to a single plate will leave the machine very weak IMO.
Nothing wrong with the format great for light duty wood use but I would seriously look to beef up the gantry.

If you must use profile then why not use 45x90 sandwiched between 2 plates like the pics below.
The wider profile helps with ridgidity and mixed with the extra plate it would be very strong. Plus It has the advantage of protecting the screw with just a slot for the Y aixs ball nut mount bracket which is covered with simple brush draft excluders but still allowing ballnut bracket to slip by.Access is simple by unscrewing the rear plate.
The slot is easy cut into the plate by drilling hole either end then simply running circular saw up each side.

Keep up the good work. .:toot:

deannos
23-01-2012, 08:49 AM
Jazz,
Is the plate with the slot still ali or wood, i'm confused with cutting with a circular saw. If i did beef the gantry up this way would i then be able to cut anything other than light wood, would it be able to mill aluminium if required

m.marino
23-01-2012, 09:58 AM
Dean,

From what I know of that design it is aluminum plate and you can cut it wit a circular saw blade for metal cutting. As far as cutting heavier materials, I don't know but have seen set ups like this used to cut metal, so depending on a few issues of torsion it should be possible. The question comes in how much twist or flex you will get while doing so and how that will limit you cutting depth.

Michael

JAZZCNC
23-01-2012, 03:45 PM
Jazz,
Is the plate with the slot still ali or wood, i'm confused with cutting with a circular saw.

Yes it's Ali plate and yes it cuts very easy using hand held circular saw used for cutting wood so long as it has a TCT tipped blade, preferably with a thin curf.
There are purpose metal cutting blades as well but can be expensive and not required if just doing the odd bit of Ali cutting.
You could use a jigsaw but the hand held makes quick work of it and cuts a nice straight line.(Better if you use a guide or piece of wood to run against)
The hand held will cut 10mm plate in one pass just lower the blade in nice and slow and push at a slow feed. Make sure you use goggles and long length sleeves because the chips burn like crazy.

You can even cut Ali with hand held router if you take shallow depth pass's. Thats how my first machines gantry sides and Z axis where cut, I made a MDF template then used TC 6mm straight top bearing guided wood bit and cut around the templates in 0.25 pass's.!! . . . Scarey shit at first and took awhile to do but it worked ok.


If i did beef the gantry up this way would i then be able to cut anything other than light wood, would it be able to mill aluminium if required

With this setup you'll be ok for anywoods really so long as your not expecting to cut 20mm in one pass.!! and my comment about light wood use was aimed at your first design mostly.
Regards cutting Aluminium then yes it will but you'll need to be sensible, don't expect it to take 2-3mm depth pass's or even 1-2mm. You'll be in 0.25-0.75mm Max area for acceptable results. That said this is still usable thou and if your realistic with DOC/FEED rates etc then it'll be ok.

jcb121
23-01-2012, 04:23 PM
My advice on sketchup, I see you are scaling the supported rail and the mounting blocks as one,

If you double click the entity, then you will be able to select them separately and then select the rail and press "S" then drag it to the length needed.

deannos
23-01-2012, 06:33 PM
If you must use profile then why not use 45x90 sandwiched between 2 plates like the pics below.
The wider profile helps with ridgidity and mixed with the extra plate it would be very strong.

Jazz,
I don't mind whether i use profile or not is there something else i could use

deannos
23-01-2012, 06:33 PM
My advice on sketchup, I see you are scaling the supported rail and the mounting blocks as one,

If you double click the entity, then you will be able to select them separately and then select the rail and press "S" then drag it to the length needed.

Thanks for that tip, i thought it didn't look right but couldn't put my finger on it

JAZZCNC
25-01-2012, 12:27 PM
Jazz,
I don't mind whether i use profile or not is there something else i could use

Well seen as your using steel for the frame then I'd probably look towards using that. Simplest way would be an I beam RSJ type beam.
Would get 180x100 for about 30 if your buying steel for rest of machine. You can buy 1500mm length from Metals4U for 37 plus postage.

This would be an easy option and plenty strong enough for your needs, easy to fasten rails, screws etc.
You will need to make sure you get a nice straight and flat piece then may still have to do a bit of cleanup with grinder/sander and straight edge to make it's flat but it makes a very strong gantry. (Don't be fooled into thinking profile is always straight or flat.!!)
The weight will be slightly higher but to be honest for a wood router if mixed with a strong spindle/big router the extra weight can be an advantage and allow deeper cuts which offsets the slightly lower feeds.

The other way is to use 80x40 box section in a similair setup to the Cad model using profile, just slightly cheaper than profile at 35 for 7.5mtr.

deannos
25-01-2012, 03:01 PM
Well seen as your using steel for the frame then I'd probably look towards using that. Simplest way would be an I beam RSJ type beam.
Would get 180x100 for about 30 if your buying steel for rest of machine. You can buy 1500mm length from Metals4U for 37 plus postage.

.

I like the idea of using the RSJ, less for me to do. I assume i wouldn't need to box this in and it can be left as is, would it need support or stiffeners at each end.

JAZZCNC
25-01-2012, 05:13 PM
I like the idea of using the RSJ, less for me to do. I assume i wouldn't need to box this in and it can be left as is, would it need support or stiffeners at each end.

Here's how I'd go about it.! . . .Miniumum welding and very strong. I've drawn it with welded corner braces but this could be built without any welding what so ever just drill and bolt if you used 19mm plate for the corner brackets.
Personally I'd weld 5mm plates in the corners and proably a few extra braces across it's length round the back side to just help reduce resonance but again these could easily be bolted, just weldings quicker.
I'd also probably incorparate a thin detachable cover plate on front with slot in it using brush's like in other design just to protect the screw from debris, esp if main use is wood. For the little extra work and expense it will save the screw big time. You could use flexible consertina type covers but they are expensive and can be akward to setup.


EDIT: OR you could just cut a slot in the RSJ and mount the screw on back side and cover with thin plate, something like clear perspex so you can see workings.!! Added pic (RSJ4) with slot in couldnt be arsed to alter sides or move motors but again you'll get the idea.
It will weaken the gantry thou and some extra bracing along it's length would be required.

Jonathan
26-01-2012, 12:24 AM
The torsional stiffness of I section is very poor compared to RHS or box section and clearly the ganty twisting directly leads to tool deflection (proportional to the extension of the Z-axis) parallel to the Y-axis. For the same mass you should be able to make a much stronger gantry with RHS, or an equally strong but much lighter gantry. The difficulty is the position of the Y-axis ballscrew is sub-optimal, but you should be able to get it close to between the rails. That's why people often use two pieces for the gantry with the ballscrew between. That also allows adjustment to get the rail mounting surfaces parallel.

Routercnc's spreadsheet posted a few years ago on this forums lets you compare the sections easily.


With this setup you'll be ok for anywoods really so long as your not expecting to cut 20mm in one pass.!!

I've done that in plywood...pretty scary at first but the second cutter survived!

JAZZCNC
26-01-2012, 01:35 AM
The torsional stiffness of I section is very poor compared to RHS or box section and clearly the ganty twisting directly leads to tool deflection (proportional to the extension of the Z-axis) parallel to the Y-axis.

There you go again Jonathan completely missing the point.!! . . . . YES AGREE there are stronger and lighter ways to build a Gantry BUT and here's the point.!! THIS WILL EASILY HANDLE THE JOB OF CUTTING WOOD AND BE MORE THAN STRONG ENOUGH . . very easy to build and cheap easy to source.

From what I under stand Dean intends mainly wood use so the Z extension will be minimal, or should be for best results, so given that it's only 1500mm long and twin screw driven being securely tied into both the X axis bearing plates and the gantry end plates and with a good steel thickness on RSJ then the twisting(torsion) will be minimal.

Not every body has the skills or equipment you and I have so minimising the equipment required but still having a strong gantry doesn't get any easier than this.! . . .Drill and saw/grinder are the only tools required.

deannos
26-01-2012, 10:57 AM
I would of also thought with the end plates it would be more than up to do the job i require. But i have to bow to knowledge of you guys who know more than i ever will. Was poking around on another forum and found this, but unfortunately i don't think there is a build log.5271

routercnc
26-01-2012, 01:47 PM
Hi Deanos,

I've compared the following 1500mm long steel gantry shapes for tool deflection due to gantry twisting (when cutting wood in the X direction):
_____________________I beam__RHS____RHS
Width _______________100_____100_____100
Depth _______________180_____180_____180
Flange/wall thickness ___6________6_______3
Mass (kg) ____________26______38______19

Deflection (mm)______0.021___0.00037__0.00068

Clearly RHS is better, but I beam is also 'useable' for cutting wood. In the end it is about what is sufficient for your needs and what you can comfortably make.

Swarfing
26-01-2012, 01:53 PM
The torsional stiffness of I section is very poor compared to RHS or box section and clearly the ganty twisting directly leads to tool deflection (proportional to the extension of the Z-axis) parallel to the Y-axis.
Jazz i'm with you on this one, i would love to see Jonathan try and twist an RSJ mounted on his machine? you are still talking 5/6mm minimum steel plate.

Jonathan
26-01-2012, 01:55 PM
There you go again Jonathan completely missing the point.!! . . . . YES AGREE there are stronger and lighter ways to build a Gantry BUT and here's the point.!! THIS WILL EASILY HANDLE THE JOB OF CUTTING WOOD AND BE MORE THAN STRONG ENOUGH

Of course it will handle cutting wood well. A machine built from wood is capable of cutting wood but that doesn't mean you should make one.

My aim is to make as good a machine as I can, not one that's just meets my current needs.


From what I under stand Dean intends mainly wood use so the Z extension will be minimal, or should be for best results, so given that it's only 1500mm long and twin screw driven being securely tied into both the X axis bearing plates and the gantry end plates and with a good steel thickness on RSJ then the twisting(torsion) will be minimal.

A substantial joint at the ends, i.e. welded plates, will help but it's not the whole story. Good end fixity makes a big difference to beam bending but not torsion.

For instance, using the spreadsheet to calculate torsional stiffness relative to 180x100 RHS:
180x100 RHS section, torsional stiffness, 1
180x100 box section, 3mm wall, torsional stiffness, 103
180x100 box section, 5mm wall (same mass as RSJ above), 164
100x50 box section, 3mm wall (biggest from metals4u), torsional stiffness, 13.9
152x12.7 plate, torsional stiffness, 1.1

So you're talking 10-100x difference. The mass of the RSJ is greater than all of the above and the bending parallel to Y on all the above sections, except the plate, is negligible (much less than the torsional deflection).

So I suggest deannos should use the design Jazz suggested earlier with two 80x40 box sections, with the ballscrew between and a plate on the back. Easy to make with hand tools, no worry about parallelism of the rail mount surface and bending is less than all of the cross sections discussed above according to the spreadsheet. Unfortunately can't calculate torsional stiffness without FEA but it's clearly less.

JAZZCNC
26-01-2012, 02:06 PM
I would of also thought with the end plates it would be more than up to do the job i require.

Yes Dean it will be more than up to cutting wood.! . . . . There are issue's which arn't Ideal like easy setup of parallel rails like Jonathan touched upon. . . But if like I said with carefull selection of material they will be very close and then It's not difficult to manipulate them parallel with filling/grinding and spacers/shims.
My experinece with Cheap chinese round rail is that it's not straight or consistant in dimesions along it's length, just as the bearings mounting surfaces are rarely level, flat or true so shimming is nearly always required to fine tune. . . BUT AGAIN . . . It's down to intended use and for machineing wood then the tolerences are much lower and forgiving so can be tolerated.
If you want to wear belt & braces (excuse the PUN!!) and just add some bracing along it's length.!!


Regards that Pic you posted I'm pritty I've seen that before and it was actually built to cut stone.?? . . . . But don't quote on that!!. . . . But I've certainly seen one built the same that was cutting stone and it actually came up for sale on Ebay.

deannos
26-01-2012, 03:16 PM
Regards that Pic you posted I'm pritty I've seen that before and it was actually built to cut stone.?? . . . . But don't quote on that!!. . . . But I've certainly seen one built the same that was cutting stone and it actually came up for sale on Ebay.

Jazz,
I found this on cnczone and reading his posts i think you are correct and it was used for cutting stone, he was in Indonesia. If i chose the earlier option of 2 box sections sandwiched between plate, would it be ok to use 10mm plate and use 20mm on the Z axis only. Just want to weight up all the options at the moment.

Just out of interest, i'm looking at using 1605 and 2005 ball screws, belts and pulleys if possible. I had a go at the weekend cutting the infamous Aztec/Mayan calendar, approx 12" size, after 3 hours i had cut less than a 1/5th. How much faster roughly would using ball screws make a difference.

Jonathan
26-01-2012, 03:46 PM
20mm is a good size plate for the Z-axis.

The efficiency of ballscrews is roughly twice that of ACME screws, so it will be significantly faster. For the Aztec calender acceleration is much more important as it's lots of tiny moves. The bearing nut thingy you're using will make the difference slightly less. The main advantage is 5mm pitch versus 2mm pitch - the kinetic energy in the screw is significantly less if it's rotating 2.5 times slower.
The most accurate comparison you're going to get is comparing with my machine, as I sold you the screw. I got 6m/min with the screw your using and 42:13 pulleys on Y. I ran it at less than that with smaller pulleys as that was too close to the critical speed of the screw (see my build log for actual values). With 42:14 (I think) and a 10mm pitch ballscrew I got 60m/min. That's much more than you'll ever need so I've left it on close to 1:1 to get better resolution and acceleration.

deannos
26-01-2012, 03:54 PM
20mm is a good size plate for the Z-axis.

The efficiency of ballscrews is roughly twice that of ACME screws, so it will be significantly faster. For the Aztec calender acceleration is much more important as it's lots of tiny moves. The bearing nut thingy you're using will make the difference slightly less. The main advantage is 5mm pitch versus 2mm pitch - the kinetic energy in the screw is significantly less if it's rotating 2.5 times slower.
The most accurate comparison you're going to get is comparing with my machine, as I sold you the screw. I got 6m/min with the screw your using and 42:13 pulleys on Y. I ran it at less than that with smaller pulleys as that was too close to the critical speed of the screw (see my build log for actual values). With 42:14 (I think) and a 10mm pitch ballscrew I got 60m/min. That's much more than you'll ever need so I've left it on close to 1:1 to get better resolution and acceleration.

Ok thanks Jonathan,

What is your thinking on using 10mm plate on the Y gantry, or would it be better using 20mm because of the length

JAZZCNC
26-01-2012, 04:16 PM
Hi Deanos,

I've compared the following 1500mm long steel gantry shapes for tool deflection due to gantry twisting (when cutting wood in the X direction):
_____________________I beam__RHS____RHS
Width _______________100_____100_____100
Depth _______________180_____180_____180
Flange/wall thickness ___6________6_______3
Mass (kg) ____________26______38______19

Deflection (mm)______0.021___0.00037__0.00068

Clearly RHS is better, but I beam is also 'useable' for cutting wood. In the end it is about what is sufficient for your needs and what you can comfortably make.

Ok didn't see this or Jonathans last post so this apply's to both post's.

First I'm not knocking the Calculations or saying they are wrong but your both missing the POINT. . . .!! IT WILL DO THE JOB AND DO IT GOOD.!! . . . IT'S CHEAP AND EASY.!!

It's easy to build with absolutly minimal machining or drilling, far less Jonathan than my first design which yes is stronger but much more expensive.

Jonathan good design is about building the best machine to do the intended use accurately and effiecently. A good designer will always design a machine to do the required job with a certain safety percentage designed in and no more. Any more is just wasted expense and ineffiecent.

Working On your design criteria then you FAILED because you could have used far heaver gauge box section or steel plate rather than Aluminium or why not go the whole hog and Cast some Iron castings.!!. . You had the knowledge,equipment and abilty so why not.? . . . . . Because it didn't warrant the extra cost and effort to accumplish what you intended to do with the machine.

I've just checked price with my supplier and I can get 1x1800 & 2x1000mm 178x102 RSJ 8mm steel for 75 no vat cut to length delivered.
That will do both the gantry and the X axis. Or Just the gantry would be 37.!!

So Profile/plate way:
Ali plate 4mtr x 150 x 9.5mm = 86inc vat + 10 delivery = 96 (400mm left over)
Profile (as per my other design)1800 x 90x45H = 41.50 x 2= 83 + 10 delivery = 93 . . .or 1800x45x45 (As dean's design) =43 +10 del = 53 . . .OR. .
80x40x3 steel box section 39
Plus lots more Nuts and bolts so another 10

Total 199 OR 45x45 159 OR Steelbox 145

OR

RSJ way:
RSJ 1800x178x102 37
Nuts bolts 5 (far less required)

Total 42

Also a lot less drilling work which will also add to the cost because of worn/snapped drills.!


Now taking the RHS route and regards the Calc's and price stand point theres also the issue that like for like dimensions where used. Now 180x100x6mm RHS is not a common size and the nearist would be 160x80x6mm Which is 160 so no saving there and it won't be as easy to work with as RSJ.

Also the calculated strength of the I beam is going to go up because of 8mm thickness not 6mm and the RSH will drop slightly due to lesser dimensions, it will still be stronger but the difference is less but more the point the Ibeam which is already more than suitable will increase.!

This is my POINT.!!

JAZZCNC
26-01-2012, 04:22 PM
Dean yes 6" x 3/8" (150x9.5mm) plate would do fine and the Cad models I drew used them dimensions except for gantry sides and bearing plates which where 19mm plate and I'd recommend you use.

routercnc
26-01-2012, 09:36 PM
Hi Jazzcnc,

I totally agree with you that I beam would be sufficient for cutting wood. I just wanted to show Deanos the improved performance of RHS to explain Jonathan's point about how it could be better if you wanted to make it do more in the future.

I also can't fault your logic and argument on the cost side because that is very important for a home build.

Just for completeness, and not to start a war (!) I've done the calcs for the sizes you mention:

___________________I beam____RHS
Width _______________100______80
Depth _______________180_____160
Flange/wall thickness ___8_______6
Mass (kg) ____________34______32

Tool deflection (mm)______0.009___0.00067

[all assuming 150mm between gantry centre and tool cutting tip - the moment arm trying to twist the gantry]

So the I beam still looks reasonable.

JAZZCNC
26-01-2012, 11:00 PM
Hi Jazzcnc,

Just for completeness, and not to start a war (!) I've done the calcs for the sizes you mention:

" For to win one hundred victories in one hundred battles is not the acme of skill. To subdue the enemy without fighting is the acme of skill." (Sun Tzu)

It's Aussie day so no worries Mate.:beer:

Swarfing
26-01-2012, 11:37 PM
Looks like bloody good odds to me especially from such a simple and quick build :toot:

deannos
27-01-2012, 09:38 AM
Looks like bloody good odds to me especially from such a simple and quick build :toot:

I agree, that's why i've decided to go the RSJ route, especially as i don't have any fancy tools. But i can weld and this will be far the easiest route for me, and there won't be a lot of drilling and tapping either. The only thing that worries me slightly is the weight of the gantry, i know weight is a good thing, but would this be to much to get decent speeds. Now i'm not looking to break any speed records, just to get a reasonable feed etc. The motors i have at the moment are nema23-3NM and MSD542 drivers with 50v power supply.

Dean

deannos
27-01-2012, 09:40 AM
" For to win one hundred victories in one hundred battles is not the acme of skill. To subdue the enemy without fighting is the acme of skill." (Sun Tzu)

It's Aussie day so no worries Mate.:beer:









I count myself part Aussie, having done nearly all my schooling there, :tup::beer:

Jonathan
27-01-2012, 01:15 PM
I also can't fault your logic and argument on the cost side because that is very important for a home build.

Same here. Thought that it was obvious that you just make it as strong as you can afford. I made mine as strong as I could afford at the time, but not as well as I could and I've been waiting for the funds to improve it for some time.

One last thought:

5272

You could weld a steel sheet (red) on to the back of the RSJ (blue). Then you've got the torsional stiffness of box section and the convenience of RSJ. It needn't be very thick, I think 3-4mm sheet would be fine. Adding several of the green triangular pieces might help, but it's a lot of effort to cut them out without a guillotine. Only problem with all this is the welding might distort the top surfaces, so it's best to do it from the start.
Other option is use box section but add plates on the top and bottom so that you can put the linear bearings off center to get the ballscrew in a good position. Not sure which would cost more...


The only thing that worries me slightly is the weight of the gantry, i know weight is a good thing, but would this be to much to get decent speeds. Now i'm not looking to break any speed records, just to get a reasonable feed etc. The motors i have at the moment are nema23-3NM and MSD542 drivers with 50v power supply.

Dean

deannos
27-01-2012, 01:24 PM
Adding several of the green triangular pieces might help, but it's a lot of effort to cut them out without a guillotine.

I have a very nice angle grinder that would do the job.

Other option is use box section but add plates on the top and bottom so that you can put the linear bearings off center to get the ballscrew in a good position.

You mentioned earlier about the ballscrew being in a good position, i'm not to sure in what you mean. If you mean to bring it out closer to the Z plate, could i not use spacers on the bearings

Jonathan
27-01-2012, 01:36 PM
You mentioned earlier about the ballscrew being in a good position, i'm not to sure in what you mean. If you mean to bring it out closer to the Z plate, could i not use spacers on the bearings

The best position for the Y-axis ballscrew is between the Y-axis rails so that there can be no movement of the linear bearings without the ballnut moving. More precisely the ballscrew should lie on the plane occupied by both the Y-axis rails, parallel to the rails. With the RSJ design it's close enough, with the previous design using two 80x40 box sections and 10mm plate it would be perfect.

(meant to post this in the previous post)


The only thing that worries me slightly is the weight of the gantry, i know weight is a good thing, but would this be to much to get decent speeds. Now i'm not looking to break any speed records, just to get a reasonable feed etc. The motors i have at the moment are nema23-3NM and MSD542 drivers with 50v power supply.

As long as you use RM1610 ballscrews to move the gantry it will still be fast due to the higher pitch and more importantly get better acceleration than RM1605. You'll want a 1:1 ratio with 10mm pitch, but I used pulleys anyway to reduce resonance. You can always swap the pulleys round to get a 1:2 ratio for better resolution. If you get the end machining for the ballscrew where the pulley mounts made 8mm, same as the motors, instead of 10mm then swapping the pulleys is simple. For instance use two 15T on Y and 30T on X you can swap them all round to get 15:30 if required.
Also I got the end machining for the pulley made 25mm long instead of 15mm as it makes it much easier to align and mount the pulleys.

RM1605 may still be fast enough, but when you're getting them from linearmotionbearings2008 on eBay I don't think there's much if any difference in price between the two so no point. Especially since you can use pulleys to get effectively the same pitch (if required, for the vast majority of things it wont be) as RM1605 with better v&a as the screw is only spinning half as fast.

Swarfing
27-01-2012, 01:58 PM
Looks like the KISS approach is completely being over looked here? there looks like a complete ton of needless work for what will amount to very little gain in a home built machine. Welding all that extra in will no doubt make what will not be perfect in straightness even worse. Deanos if you want to make precision NASA approved telmetry parts go for. If you want to build parts that any motoring manufacture would be pleased with don't bother. The sort of numbers we have been looking at will not make a bit of difference to you i truly believe that. By not adding all this extra rubbish you will be keeping down the weight and expense, you can always make the parts with the machine once it is running.
KISS KISS KISS KISS

Jonathan
27-01-2012, 02:07 PM
It's only a suggestion, take it or leave it. I post these things to benefit other people who may want more from the machine than Dean.
Adding the plate to make a box is very simple and should make a big difference but if Dean never wants to cut aluminium regularly there's no point. 0.01mm tool deflection might not sound like much, but when you start cutting metals it is - surface finish, material removal rate and tool life are affected. Running the calculation with cutting force for aluminium gives 0.058mm.

I used 8mm web thickness for the RSJ, not 6mm, in all the calculations as that's a standard size - with 6mm tool deflection is about twice as much.

Swarfing
27-01-2012, 02:18 PM
Please for you

JAZZCNC
28-01-2012, 01:01 AM
It's only a suggestion, take it or leave it. I post these things to benefit other people who may want more from the machine than Dean.

Great Jonathan but in a thread like this surely the target is to help the person who's building come to a design that suits his needs not others.? Thats how approach every thread.
First and foremost I try to advise with clear uncluttered information and suggestions to help them arrive at a design that will suit the intended purpose and do it the best it can. . . No more no less.!! . . . . If I can help them achieve this in a cheap and easy way then I most certainly do and get a warm fuzzy felling doing so:naughty:

Over complicating and over building past the usuall built in safety margin is just wasteful in both time and money.!

The simple FACT to DIYCNC is that it's NOT POSSIBLE to easily and cheaply build a machine that can cut every material like a purpose built machine optimised to cut the same material . . . . Belive me because I've tried very hard.!! You either build the machine to do the very best it can at that intended job at a sensible price and accept it's short falls in other area's. . . . OR . . . . Throw lots of serious money and time massively over build and have it perform in all areas average.!

Now back to the job in hand.:rolleyes:

Dean for your MAIN need of cutting wood the RSJ will perform perfectly well without any extra bracing, welding or what ever. It will cut Ali but obviosly with restriction and greatly reduced performance compared to if it was built for that use.
Accept it's limitations and you'll love the machine which will become your faithfull servant but push it past them and you'll hate the bloody thing because it will try to kick you in the bollocks at every inopertune chance it gets.!!

Personally I'd use the RSJ but want to fill in the front and rear with thin covers, these would be serving 2 purposes with a frindge bennifit of adding strength.
Firstly functional, Secondly cosmetic, on the front they would be protecting the screw from debris with the slot idea on the previous design and on the rear it would be mainly cosmetic possibly houseing wires etc.!!. . . . but heres the fringe bennifit.?
To do this I would cut plywood braces that get bolted between the flanges and thru the web of the RSJ the covers would be just thin plywood screwed to the blocks. The bolted blocks would increase rigidity and combined with the plywood increase strength.

I've attached another pic to help explain.

Edit: Added coverd in pics for completeness.!

JAZZCNC
28-01-2012, 01:26 AM
thats one nice no nonense design jazz,:tup: mind if i pinch it:naughty:

Nope go for it Chip all my ideas are some bugger else's anyway. . . Just Jazzzzz'd up. .:heehee:

deannos
28-01-2012, 05:53 PM
Yes i'm going with the rsj as well. Its simple in its design and doesn't require any fancy tools. With its mass i believe this could just be bolted down on to a very sturdy table and save me messing about with a frame. I also think this would be easier to get square and level as well. I'm only interested in cutting wood not ali so the design suits me down to the ground. Jazz that design you have done in post 38 is excellent, looks like a million dollars but is cheap as chips:tup:. I'm going to base my design on that.

Cheers Dean

JAZZCNC
28-01-2012, 08:09 PM
With its mass i believe this could just be bolted down on to a very sturdy table and save me messing about with a frame. I also think this would be easier to get square and level as well. I'm only interested in cutting wood not ali so the design suits me down to the ground.

Here's a bit of food for thought for ya.!!! . . . . Why not build 2 small concrete block walls with a plate securely bolted down onto it. Then with adjustment jack nut n bolts thru both to level the RSJ's. Then you could just push a strong bench under neath fasten down then surface it flat and away you go with virtually no material height restriction.
Obviosly you will have Z axis travel restriction but not material height.!!. . . The machine use's and flexibilty regards material sizing become far greater.!!. . . . Imagine some one wanting an old table surfacing or V carving. . . . how easy does that become.? . Ye I know not probable but you get the idea.
The same plate/jack system would work good on a bench thou.

Some time towards the end of the year I'll be building just such a machine that use's R&P and will be used for cutting granite slabs 3x2mtr into work surfaces. This will use the same principle but have a free standing concrete table with a hydrolic tilting frame for loading slabs from near vertical to horizontal.

luke11cnc
28-01-2012, 09:36 PM
I did write a reply but I think the mod's must have it ??
James

JAZZCNC
30-01-2012, 12:19 AM
I did write a reply but I think the mod's must have it ??
James

So what did it say.?????

deannos
30-07-2012, 09:31 PM
Ok, still struggling a little with sketchup. This is my latest attempt and i have put the ballscrew on top of the i-beam. Would this work, i'm struggling with ideas on this.




Ignore this

deannos
01-08-2012, 04:43 PM
Ok, i think i'm finally getting there. All plate is 20mm thick ali and also using I-beams. I'm not sure if the screw mounts are ok doing it this way. Would the bearing blocks need spreading out more. All the rails are 20mm with 1610 screws. Some pictures to show my progress and please tell me where i have gone wrong and where improvement can be made64716472647364746475

I will have the ballscrew end machining increased from 15 to 30mm as i want to use belts and pulleys.
The RSJ's are 178x102x19mm, would it be better to use a smaller size on the gantry, 127x76x13mm.
Also just realised i haven't taken into account the thickness of the beams

deannos
02-08-2012, 12:57 PM
Ok have redone the RSJ's and added steppers.648264836484

Jonathan
02-08-2012, 07:41 PM
The RSJ's are 178x102x19mm, would it be better to use a smaller size on the gantry, 127x76x13mm.\

Although it's convenient to use RSJ on X and Y, you'd be better off using a different cross section. The torsional stiffness of RSJ is pathetic, hardly much better than a sheet, so especially on the gantry where the cutting forces will tend to twist the beam you would get a lot of deflection. Similarly RSJ is poor under shear stress, which is the case on the X-axis. To an extent you have compensated for that by using a large thickness, but with less material you could use box section and get much greater stiffness.
One reason not to use smaller RSJ is it reduces the vertical spacing of the Y-axis bearings, which is something you want to maximise.

What you've drawn is still fairly strong, so it would work - but that is purely because of the large thickness.

Try folding an RSJ cross section and a box section out of card then try and twist them and you will see how big the difference is. This spreadsheet (http://www.mycncuk.com/forums/linear-rotary-motion/2214-cnc-machine-stiffness-calculator.html) lets you compare them.

deannos
02-08-2012, 08:00 PM
Although it's convenient to use RSJ on X and Y, you'd be better off using a different cross section. The torsional stiffness of RSJ is pathetic, hardly much better than a sheet, so especially on the gantry where the cutting forces will tend to twist the beam you would get a lot of deflection. Similarly RSJ is poor under shear stress, which is the case on the X-axis. To an extent you have compensated for that by using a large thickness, but with less material you could use box section and get much greater stiffness.

Ok, would i be better using Ali extrusion, or are you talking about steel box section. What size would you suggest


One reason not to use smaller RSJ is it reduces the vertical spacing of the Y-axis bearings, which is something you want to maximise.

I'm still confused on the axis direction, by "Y" are you referring to the bearings the longer gantry is riding on

I want to get it right the first time, or as best as can be


How do you use the multi quote option, i clicked it and nothing happens

Jonathan
02-08-2012, 08:11 PM
Ok, would i be better using Ali extrusion, or are you talking about steel box section. What size would you suggest

I was thinking steel box section, but aluminium extrusion is pretty good too. If you're happy to do some welding then steel box section is the cheapest and strongest option for making a frame. The standard length is 7.5m, so it would be prudent to design the frame to use an integer multiple of 7.5m! I used 60x60mm, 3mm wall thickness box section for most of the frame and 100x60mm, 3.6mm wall thickness for the two lengths the X-axis rails mount on.

How long is the piece of RSJ you've drawn for the gantry?


I'm still confused on the axis direction, by "Y" are you referring to the bearings the longer gantry is riding on

I always call the axes on the gantry Y and Z and the other axis X. So by that definition in your case X is shorter than Y.



How do you use the multi quote option, i clicked it and nothing happens


The what.. never seen that! I just copy and paste the [QUOTE] tags in the relevant locations. I've put them in on your post for you, so if you click 'Edit Post' you can see how...

deannos
02-08-2012, 09:07 PM
[/COLOR]

I was thinking steel box section, but aluminium extrusion is pretty good too. If you're happy to do some welding then steel box section is the cheapest and strongest option for making a frame. The standard length is 7.5m, so it would be prudent to design the frame to use an integer multiple of 7.5m! I used 60x60mm, 3mm wall thickness box section for most of the frame and 100x60mm, 3.6mm wall thickness for the two lengths the X-axis rails mount on.

I can weld , it wouldn't win any contests though, i would like to keep the RSJ for the X axis


How long is the piece of RSJ you've drawn for the gantry?

It measures out at 1715mm, but could be slightly longer.

deannos
04-08-2012, 06:32 PM
Instead of using a rsj for the gantry, could i use 100mm x 60mm x 3mm steel box section. I can get my hands on a piece long enough for a tenner, and its very local.

irving2008
04-08-2012, 08:37 PM
what size rsj were you planning to use and how long?

deannos
05-08-2012, 02:29 AM
irving2008;33697]what size rsj were you planning to use and how long?



On the gantry the rsj is 178mm x102mm x19mm and is 1720mm long

irving2008
05-08-2012, 11:24 PM
I'd use the box section.

Reasoning:

a) 1.7m of RSJ @ 19kg/m = 32kg, whereas 1.7m box section @ 7kg/m will weigh 11.9kg, thats nearly 2/3 less to move around...
b) RSJ will deflect .004mm in centre under its own weight plus 0.0004mm per kg load (i.e. negligible), Box section will deflect 0.018mm under its own weight, plus .004mm per kg load. So a 10Kg z-axis will deflect the rsj gantry .008mm and the box section gantry .058mm. In the scheme of things this is negligible.

wilfy
06-08-2012, 12:01 AM
I'd use the box section.

Reasoning:

a) 1.7m of RSJ @ 19kg/m = 32kg, whereas 1.7m box section @ 7kg/m will weigh 11.9kg, thats nearly 2/3 less to move around...
b) RSJ will deflect .004mm in centre under its own weight plus 0.0004mm per kg load (i.e. negligible), Box section will deflect 0.018mm under its own weight, plus .004mm per kg load. So a 10Kg z-axis will deflect the rsj gantry .008mm and the box section gantry .058mm. In the scheme of things this is negligible.


so even though both are negligible as you put it.. you would still steer him clear of the easier/cheaper option of an rsj that needs little work over him welding box section and possibly leaving room for him to create errors...

or have i mis-understood... i'm watching this thread as the thought of rsj being an easy way compared to welding box section appeals to me

irving2008
06-08-2012, 12:12 AM
so even though both are negligible as you put it.. you would still steer him clear of the easier/cheaper option of an rsj that needs little work over him welding box section and possibly leaving room for him to create errors...

or have i mis-understood... i'm watching this thread as the thought of rsj being an easy way compared to welding box section appeals to me

Not sure i understand your logic... given a lump of i-beam or a lump of box section, you're still going to have to drill holes to mount rails etc. He was suggesting the rsj for the y-axis element of the gantry... not sure what welding is needed???

Also he says he can get a section for a tenner... the cheapest 178x102x19 rsj on ebay is 19.50/m min order 4m.. plus carriage...

wilfy
06-08-2012, 12:18 AM
ok maybe i've mis-understood the whole thing... i was under the impression that if he used box section then he would have to do some welding or atleast joining 2-3 pieces where as the rsj was a solution that didnt need any work other than attaching other parts?

my thought are that he is using 2 pieces of box to make what would be the top and bottom of the beam... but i can now see you are talking about one big piece of box the same size of the rsj... sorry my bad

Jonathan
06-08-2012, 12:29 AM
Once you include torsional stiffness in the calculation the single box section is much better than RSJ:

6517

The problem with either of these options is mounting the rails with sufficient accuracy. I doubt either steel RHS or RSJ will we sufficently accurate to mount the two rails on opposite faces, since the variation in the 'height' of the section will change the spacing of the rails leading to binding. Seems a bit risky... could fix it with shims I guess but you don't want to go there.
Instead I'd use two pieces of the 100x60 box section with one rail on each as that will be far stronger than just one and solves the problem of maintaining rail spacing.

wilfy
06-08-2012, 12:35 AM
Once you include torsional stiffness in the calculation the single box section is much better than RSJ:

6517

The problem with either of these options is mounting the rails with sufficient accuracy. I doubt either steel RHS or RSJ will we sufficently accurate to mount the two rails on opposite faces, since the variation in the 'height' of the section will change the spacing of the rails leading to binding. Seems a bit risky... could fix it with shims I guess but you don't want to go there.
Instead I'd use two pieces of the 100x60 box section with one rail on each as that will be far stronger than just one and solves the problem of maintaining rail spacing.


Thank you for that, I thought that was what was said earlier, which is why I posted what I did, however I didn't realise rsj would be just as in accurate.

How do you join the 2 pieces of box out of interest, if its welding surely this can go just as wrong no???

JAZZCNC
06-08-2012, 01:10 AM
Dean if your intention is still the same has before to only cut wood then ignore Jonathan he's talking over complicated bollocks again and it will easily do the job.

If you can get the Large box section for a tenner then obviously it's a no brainier and go for it.! . . Not disputing Box section won't be stronger but no where near has cheap or easy unless you can drop on something like this.

The RSJ will do the Job no problem the extra mass will help with cutting but does cost in acceleration and speeds.

I would how ever change the way you have the X axis bearings and use wider plate than the RSJ which bolts to it. I would then have gantry end plates which bolt to the RSJ and the bearings plates dropping down so the ballscrews can connect. This will help stiffen things up a bit.!! . . . Pretty much like I drew before.!

JAZZCNC
06-08-2012, 01:23 AM
The problem with either of these options is mounting the rails with sufficient accuracy. I doubt either steel RHS or RSJ will we sufficently accurate to mount the two rails on opposite faces, since the variation in the 'height' of the section will change the spacing of the rails leading to binding. Seems a bit risky... could fix it with shims I guess but you don't want to go there.
Instead I'd use two pieces of the 100x60 box section with one rail on each as that will be far stronger than just one and solves the problem of maintaining rail spacing.

Rubbish.!! What makes you think both these will be flat surface or straight .? Single or 2 pieces make no difference the surface will still need some work and while 2 pieces will allow easy general positioning they won't be anywhere near parallel all along the length. If the section has any bend then it will still need grinding or shimming at several points and just because you have a rail on each piece doesn't make it any easier.
It's not difficult with a decent straight edge and files,grinder to the bring the main reference surface upto scratch then it's just a case of shimming or grinding the other rail surface parallel.

deannos
06-08-2012, 01:54 AM
Ok, now we are talking about the weight issue and moving the mass around and me still a complete novice at this. My question is would the steppers i already have be ok for the job. They are nema 23, 3nm (M60STH88-3008DF) and the drivers are MSD542 with a 48v power supply. I'm thinking that i would just have to change the drivers and get a 70v power supply

irving2008
06-08-2012, 11:21 AM
Now I've read the whole thread, looks like we repeated the discussion on box v rsj from last January lol. JazzCNC is right in that either will do and arguably the rsj is the simpler to construct with, but lets examine the 'weightier' issue of a 40kg gantry (32kg rsj + other parts) vs a 20kg gantry (12kg box + other parts). You say, from earlier, that you plan on using 16mm screws x 2, each 800mm long driven by 2 slaved motors @ 3Nm each on 48v.

A rough calculation suggests that would be good for:

rsj: 9m/min cutting and 16m/min rapids
box: 11m/min cutting and 20m/min rapids

given the same acceleration. If the former speeds are good enough (and I think they are IMHO) then the choice is down to personal preference; either will work.

There is no need to increase the driver voltage, upping it from 48v to 60v has a marginal effect (increases the rapids on the rsj version to 18m/min, doesn't justify the extra expense IMHO).

One other consideration. the lower mass of the box version would allow one motor to drive both X screws at approx 6.4m/min cutting and 11.5m/min rapids @ 48v. Again upping the voltage has relatively little effect, increases rapids to 13.3m.min. If these speeds are acceptable, then this could mean buying one less driver and stepper motor and a smaller PSU (but adding pulleys/belts to the cost). So you need to factor this as well.

deannos
06-08-2012, 01:57 PM
rsj: 9m/min cutting and 16m/min rapids
box: 11m/min cutting and 20m/min rapids


Well these speeds are plenty enough for me, a hell of a lot faster than what i'm getting now. My plan is to use 1 motor and belts and pulleys, so the box section it is at the moment. Plus i would use less ali plate in the Z axis. Also the price is right as well, but i'm waiting on some quotes for rsj,also local so could change, but would then have to factor in the extra stepper on top. Also i guessing i can use just 1 piece of box section and not have to double it up.

JAZZCNC
06-08-2012, 07:39 PM
You say, from earlier, that you plan on using 16mm screws x 2, each 800mm long driven by 2 slaved motors @ 3Nm each on 48v.

A rough calculation suggests that would be good for:

rsj: 9m/min cutting and 16m/min rapids
box: 11m/min cutting and 20m/min rapids


Whattt.??? . . . Irving you been sniffing solvents or something.? No way will he get 9m/min cut and 16M/min rapids with 48V and 10mm pitch dragging an RSJ that weighs 40Kg and would be lucky if would get that if it was Box section and weighed half the weight.? So certainly won't get get 20M/min rapids and 11M/min cut.??

This is what I mean about calculations and reality not being the same.! The real figures will be much less at this 48V voltage. The fact the motors are slaved dictates they need to be slightly detuned to avoid one stalling. The real figures to avoid stalling and keep accuracy by not losing steps under Acceleration/De-acceleration and take into account the DIY build factor will be around 8-9M/min rapids and 6-7M/min cutting with 48Vdc if your lucky.!

But it actually gets a bit worse because at 48V on 50V drives then he's too close to the drives voltage limit so for the drives safety, voltage around 44-45 will be best. This will drop speeds ever so slightly.!
At 48V the 50V drives will probably handle the odd spike back EMF will produce but they are still running at there upper limit so there life expectancy will drop.
Now the 75V drives and around 65V will give better speeds and still not be pushing the drives to the max so IMO they are very much worth the extra.

Dean don't expect much above 11-12M/min rapids and 8-9 M/min cutting and expect to keep good stability and accuracy even with the 75V drives and running 65-70V voltage. Yes with lighter gantry you'll get a bit more speed but nothing to shout about and bare in mind with real conservative figures of around 9-10M/min Rapids and 7-8M/min cutting you'll still have plenty of speed for cutting woods and know the machine will be reliable.!

Keep it real.!!

John S
06-08-2012, 08:37 PM
this is what i mean about calculations and reality not being the same.!

Keep it real.!!


rotflmao.......................................

JAZZCNC
06-08-2012, 08:49 PM
rotflmao.......................................

Ye does sound a bit ALI-G. . . . But know I'm correct that perfect world calculations often don't match real world DIY reality.??? . . . Thou so long has it's made your Ugly mug smile John it's made my day. .:thumsup:

irving2008
06-08-2012, 10:37 PM
OK OK.. I should have qualified that thought process with 'theoretically'...

On a serious note, the laws of physics don't change, so if you're not getting within 70 - 80% of the theoretical numbers then something is very wrong. Now I don't profess, Jazz, to have your experience (or John's) of building these things, I'll admit I'm an amateur in the CNC world, but I've built, tuned and fettled enough race engines and other electro-mechanical systems to know that things generally, in my experience, behave the way I expect them to. For example a 10mm pitch ballscrew should generate 50N of force per Nm of torque and thats enough to accelerate a 50kg mass at 0.1m/s^2 i.e a velocity of 6m/min after 1 sec and 12m/min after 2sec. Now I'll accept that the error in the theoretical calculations above is an assumption of infinite travel. Of course, in reality on a 1m bed you'll need to start decelerating after 3secs in order not to run off the end (assuming your stopping torque is the same as your running torque), at which point you'll theoretically be doing 18m/min - assuming your motor is still producing sufficient torque at 1800rpm. So your overall transit time over the metre is around 6 secs minimum (probably closer to 7 or 8sec), which is an average speed of 7.5 - 8.5m/min, close enough to your 9m/min.

JAZZCNC
07-08-2012, 12:23 AM
at which point you'll theoretically be doing 18m/min - assuming your motor is still producing sufficient torque at 1800rpm.

Ok first I know people(some) think I have no respect or time for the Law of physics but they'd be wrong.!! . . . I'm realistic not stupid.!!

But none of the calculators allow for, neither can they really, all the other outside factors that DIY building create. They expect, Nah rely on every component being perfect and exact to spec with very little to no physical restrictions.
I don't disagree and can't or wouldn't due to the law of physics that the forces are correct but the forces are not the problem and they can only be realised from what they are connected too and this is where it all goes Pete tong.!!

Your theoretical 18m/min requires the stepper to give usable torque at 1800rpm.!! . . . At 1800rpm stepper motors couldn't pull the skin of rice pudding let alone a 40KG gantry and with only 48V they would struggle get near 1800rpm and have enough torque left to turn the screws with nothing connected.

Couple these things with other build and cheap component issues and the REAL figures are far from the theoretical figures. . . This is all I'm trying to say and get over but If my saying this upsets anyone who's into specs and calc's then I'm afraid it's "Tuff shit" it's true and realistic..!! . . . Ence . . KEEP It REAL.!!

irving2008
07-08-2012, 12:53 AM
Ok first I know people(some) think I have no respect or time for the Law of physics but they'd be wrong.!! . . . I'm realistic not stupid.!!

But none of the calculators allow for, neither can they really, all the other outside factors that DIY building create. They expect, Nah rely on every component being perfect and exact to spec with very little to no physical restrictions.
I don't disagree and can't or wouldn't due to the law of physics that the forces are correct but the forces are not the problem and they can only be realised from what they are connected too and this is where it all goes Pete tong.!!

Your theoretical 18m/min requires the stepper to give usable torque at 1800rpm.!! . . . At 1800rpm stepper motors couldn't pull the skin of rice pudding let alone a 40KG gantry and with only 48V they would struggle get near 1800rpm and have enough torque left to turn the screws with nothing connected.

Couple these things with other build and cheap component issues and the REAL figures are far from the theoretical figures. . . This is all I'm trying to say and get over but If my saying this upsets anyone who's into specs and calc's then I'm afraid it's "Tuff shit" it's true and realistic..!! . . . Ence . . KEEP It REAL.!!

Hey, no offence taken Jazz, I am a great fan of the try it and see school... My father was a toolmaker and a marine engineer and couldn't work the physics or maths to save his life... but he still made some great stuff and mostly it worked first time. And yes, I am pefectly aware that a stepper has bugger all torque at 1800rpm if it can get there at all, in fact the point I was making, clearly badly, is that while in theory you'd still be accelerating at the point you'd need to start decelerating in reality you'd be at some lower speed before that and therefore your average over the distance would be less than the theoretical.

IMHO the purpose of the theoretical calculations, recognising they can't model every real-world situation (but can get very close if you can identify all the 'gotchas') is to see if you're in the right ballpark... if the theoretical numbers come out below what you want to achieve then you know there is no point going down that route. On the other hand, if they come out way above then you know its possible, how close you get is then determined by how near to the ideal you can make it - and my experience is that its easy to get within 70%, 85-90% is doable with care, >90% is hard. If they are close you know you've got a marginal design.

deannos
07-08-2012, 01:14 AM
Ok, here is my latest attempt, trying to incorporate every thing that has been suggested. So i will be using 20mm supported rails on every axis and 1610 ballscrews on every axis, along with belts and pulleys. The 2 rsj's will be 178mmx102mmx19mm and the gantry is 100mmx60mmx3mm steel box section. The gantry end plates and bearing plates are 20mm steel. The Z axis will be using 20mm ali plate. I have spread the gantry bearings out as been advised. Hopefully the drawings with dimensions will help.
65286529653065316532

The rails are 300mm,800mm and 1400mm. The screws are 350mm,800mm and 1450mm long

Also now confused after reading comments on the other post about the "effect of forces on gantry cross sections" and the following was mentioned-

I don't like box section for gantry's has it can produce resonance and vibration unless thick walled.? The bolted together extrusions are far denser therefore absorb vibrations far better.!! . . .Any resonance will transfer thru to the finish.

Am i going round in circles:dispirited:

JAZZCNC
07-08-2012, 01:22 AM
IMHO the purpose of the theoretical calculations, recognising they can't model every real-world situation (but can get very close if you can identify all the 'gotchas') is to see if you're in the right ballpark...

Yep I agree can be ok for a rough ballpark (Thou yours did seem a bit off base.!!) . . . You only have to look to the BIG BOYS in theoretical design and performance like F1 teams and see that even they can't predict and 100% confidently model every outcome.!



Hey, no offence taken Jazz,

Good now give us a hug.!!. . :couple_inlove:

JAZZCNC
07-08-2012, 01:33 AM
Ok thats good but bring the screw to the front, will be much stronger having the ball-nut close the Z Axis back plate.

Have you got the 20mm steel plate.? If not I think you'll maybe change your mind when you see the price.!! It's not really needed either and I'd use ali for easy working.

deannos
07-08-2012, 01:37 AM
Ok thats good but bring the screw to the front, will be much stronger having the ball-nut close the Z Axis back plate.

Ok, thats no problem, i will do that. Is this to prevent racking etc


Have you got the 20mm steel plate.? If not I think you'll maybe change your mind when you see the price.!! It's not really needed either and I'd use ali for easy working.

No i haven't got any steel plate and a quick google has made me change my mind, but if i use ali how would I join this to the steel gantry?

JAZZCNC
07-08-2012, 01:39 AM
Also now confused after reading comments on the other post about the "effect of forces on gantry cross sections" and the following was mentioned-

Am i going round in circles:dispirited:

Dean don't worry about it your only cutting wood the box section will easily handle it. The box can resonate but cutting wood it won't really matter or show.
There are also ways around this if it does by filling with sand. So long has the resonance doesn't affect the motors then you won't have problem and because your using belts then this won't happen and why it's good idea to use belts.

JAZZCNC
07-08-2012, 01:52 AM
No i haven't got any steel plate and a quick google has made me change my mind, but if i use ali how would I join this to the steel gantry?

Bolt or weld Angle brackets to box then bolt thru Ali plate into brackets.

deannos
07-08-2012, 01:55 AM
Bolt or weld Angle brackets to box then bolt thru Ali plate into brackets.

Excellent, an easy solution i didn't even think of.
cheers Dean

deannos
07-08-2012, 03:41 PM
I have moved the ballscrew to the front of the gantry and will be using 20mm ali instead of steel plate, too costly. Have added some steel angle to corners to connect gantry to end plates.65336534

deannos
12-08-2012, 09:01 PM
Would this design be ok, i thought i would use some 100x60 box section as bearing plates. I would have some left over from the gantry and it saves on the Ali plate. The extra height would help with the bed, bit more room to play with. This box section is only 3mm thick, is that ok. I have used 300mm, 2 x 800mm and 1400 SBR20mm rails. The ball screws are 350mm, 2 x 800mm and a 1450mm length.

65826583

wilfy
13-08-2012, 12:04 AM
2 questions for me that dont mean much to your build sorry :D firstly is that still an RSJ you got across the Y if so your second picture doesnt make it look like that... petty i know..

EDIT: oh scrap that i just read it's box section... my misunderastanding eek... either way second question applies

secondly how do you plan on fixing the box section to what i think is the RSJ?

deannos
13-08-2012, 12:22 AM
secondly how do you plan on fixing the box section to what i think is the RSJ?

The gantry is box section and this will be bolted/welded to the bearing plates. I have put some steel angle holding the Gantry ends to the end plates as well, but the plates will also be bolted to the bearing plates. Rsj is only used on the base "X"

A couple more pics, it might help658465856586

wilfy
13-08-2012, 09:35 PM
may i ask how much you are pricing all the metal work up to? i really like the look of this design and cant imagine mine being too far away from this so an idea of cost would be awesome, and if you could recommend the sites you've found your prices from that would be great

deannos
16-08-2012, 04:09 AM
may i ask how much you are pricing all the metal work up to?


I will do this at week end.

I've had another play around and came up with this idea, if this is any good i feel it would be easier to square every thing up.

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deannos
18-08-2012, 02:06 PM
Went to pick up my cheap box section 100mm x 60mm and it was bent, so left it. But got 2 pieces of RSJ 160mm x 90mm x 7mm x 2000mm for 20 on ebay and local for pick up. I've done a few more workings on my last design, but as there were no replies, it's probably no good. Am i going backwards in my design, i have an idea in covering the 2 outside ball screws using tumble dryer venting duct and curtain wire, it might work.

All the red/brown areas are 40mm x 40mm steel box section, that is reasonably priced. All the ali is 20mm except for the motor mounts where i have used 10mm, milled to 3mm for clearance.

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The screw lengths and rail lengths are still as quoted a couple of posts ago. I have at the moment got 1610 on the Z, reading through some other posts it seems i would be better with 1605 on Z, is that correct. Also I'm looking at going with 1:1 ratio with pulleys, would that be OK.

If i have made a big mistake with this design, please let me know. If you want the file to check it out, I'm willing to send it. I'm itching to place an order with chai.

WandrinAndy
18-08-2012, 02:46 PM
I'm itching to place an order with chai.

That makes at least two of us Dean! I'm finding that the tweaking, particularly around aligning multiple pulleys and belts, is taking quite long but reckon it's worthwhile getting this right up front in the virtual world.

Btw, your design is looking great to this newbie. It amazes me how many design permutations there are... Suppose it's a good thing as it provides more ideas for us all to crib!

JAZZCNC
18-08-2012, 06:23 PM
Dean go with 1605 for the Z axis for the extra resolution. Speed won't be a problem over this short distance.
Also the plate on the rear of the Y axis isn't needed and just costing money and weight it adds very little to strength. Seen has you have room on the Y axis at each side then if you want to stiffen up the joint between bearings a front plate then just use a " L " bracket plate on the side. This will add much more strength for fraction of the cost.
Thou if you use decent sized bolts then even this isn't needed.!

Regards the Gantry design then again I urge you to have some form of gantry sides that ties into the bearing plates which fasten to the RSJ. This will help greatly with twist and resonance, if you don't then I think you will have some.?
Gantry sides that dropped would allow the screw bolt to the web of the RSJ and do away with stuck up in air screw.? Both will work but dropped its out the way of chips and being caught with material etc when loading.!

deannos
19-08-2012, 12:42 AM
Right taken on board what Jazz has suggested and more or less gone back to my earlier design. Instead of 2 steppers on the X, i will use 3 belts and 1 stepper.
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wilfy
19-08-2012, 01:40 AM
looks awesome now get it built and inspire me please :D

JAZZCNC
19-08-2012, 02:38 AM
Right taken on board what Jazz has suggested and more or less gone back to my earlier design. Instead of 2 steppers on the X, i will use 3 belts and 1 stepper

Just the sides would have been enough.? How wide is this machine.? Looks wide so I'll warn you belts this wide are not easily found and you may have to get them custom made.? I did and my machine looks narrower than yours.!
Has much as I don't like slaved steppers I have to say at this width then they may be a better option,! And despite having to tune them slightly slower to stop stalling/racking then With 10mm pitch screws you'll still get decent speeds for cutting wood so shouldn't be too much of an issue.! . . If your feeling flush with cash Buy some of the lead-shine digital drives and you can even be protected from racking if you take advantage of the anti-stall feature built into them.!

While I'm here and commenting then got to say not keen on the Z axis setup either.? your putting all the weight of the stepper and screw with it's bearing blocks on the front plate.??
Looks like you have plenty of length to the back plate to switch them round putting screw and motors on the moving y axis so just ball-nut is attached to front plate. The Z axis then only has to lift it's own weight plus spindle so higher acceleration can be achieved. Higher Acceleration is very handy on the Z axis esp when it comes to 3D work or V carving etc.

Sorry to keep throwing curved balls but you keep sticking your head up .. .Lol

deannos
19-08-2012, 02:53 PM
Just the sides would have been enough.? How wide is this machine.? Looks wide so I'll warn you belts this wide are not easily found and you may have to get them custom made.? I did and my machine looks narrower than yours.!

It's just over 1500mm wide, so gone back to slaved motors



While I'm here and commenting then got to say not keen on the Z axis setup either.? your putting all the weight of the stepper and screw with it's bearing blocks on the front plate.??

Changed it round as you suggested


Sorry to keep throwing curved balls but you keep sticking your head up .. .Lol


Keep throwing them Jazz, would rather i cock up on the design stage then make a lemon.

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m.marino
25-08-2012, 04:00 PM
Nice looking design. One question is are you planning on indexing your plates and rails? Not only to make assembly and truing of the machine much easier but also to allow for maintenance and any type of take down that might need to happen during the life of the machine. Outside of that, looking really nice and best of luck with the build. Jazz is quiet correct in that IF you can afford digital drivers go with them; I upgraded to AM882's and the difference is night and day. I have had my machine up to 11.5m/min acceleration with 2.25m/sec^2 acceleration and not have it stall (It is a bit scary seeing that speed on my machine). My normal setting is 6.5m/min V and 1.5m/sec A and I have nice smooth movement. I have done basic tuning on the drivers and have the dampening tuned to mid zone.

Michael