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15 Attachment(s)
Aluminium FEA optimalized CNC router
I few weeks ago, I decided to get a CNC router to cut foam, carbon fiber and maybe some aluminum. I had also decided not to build one myself, because I knew router building often end up as the new hobby instead of the hobby you originally built the router for. Then someone directed me to this forum and all my plans changed.
I am now planning to build an aluminum-framed router that will eventually have capability to cut different ferrous alloys. In addition, I hope I can do some high-speed tool-paths in aluminum. In the early stages of the design, I planned to use aluminum profiles for the build, without any need for welding, but profiles are expensive and did not have the stiffness I wanted. Then I went on to steel, but that got to heavy. So now I am going to use 60x60mm t=4mm aluminum square tubes welded together. I have to practice my aluminum welding some more before I start with the build. I have done FEA on most of the build, where I started with requirements of a frame stiffness of 10-20 N/μm (10'000 N/mm - 20'000 N/mm). Deflection is proportional with force so I have checked the stiffness with lower forces and then multiplied up to 10'000 N and 20'000 N. I have done many iterations on the frame and the FEA images under is only the most relevant for the current design.
Planned working area is 1000x500x250mm
Complete assembly
Attachment 18301
The plan is to use 20mm profile rails and 16mm ballscrews on all the axis. With dual 1000mm drive one the X-axis. I'm going to use nema23 stepper motors but i'm still uncertain on the torque requirements I have to do some more calculations there. Though it seems like most of the steppers have a very high corner speed and to utilize all the torque and speed of the motors they should be geared down about 3:1. Any thoughts on this?
Base assembly (500N loads)
Attachment 18300
Attachment 18291
Stiffness; 223 N/um. I tried some different setups for vertical loads on the base. 5 vertical supports on the sides gave 4.8 times more stiftenes on the worst case compared to 3 vertical supports.
Attachment 18292
Stiffness; 53 N/um. No need for cross bracing on load in the X axis it's more than stiff enough.
Attachment 18294
The weak link where the forces in the Y axsis, this was fixed with some side bracing
Attachment 18293
Stiffness; 51 N/um. The side bracing gave 4.7 times higher stiffness. Success! (I tried a lot of different potential setups before deciding on this one)
Gantry (100N loads)
Attachment 18302
The whole weight of the gantry including the Z-axis came to 32kg, i'm going to see if I eventually can cut the weight down. I had hoped for something in the range of 20kg.
Attachment 18296
Single aluminium tube thick gantry. Were within 10 N/μm but not 20.
Attachment 18295
Stiffness; 32 N/um. Double thickness improved the stiffness 2.7 times, and the weight gain was small compared to the gain in stiffness.
Z - axis (100N loads)
Attachment 18305Attachment 18303Attachment 18304
The Z -axis ended up on 12kg. I have looked for ways to reduce the weight but often the stiffness suffers.
I'm going to use a 2.2kW water-cooled spindle. However if it is going to be use for ferrous alloys I have to gear it down to reasonable speeds. The plan is to use a belt reduction, but it's probably going to be a later update.
Under is some pictures of the results on the Z-axis. This is clearly the weakest link on the whole machine. It's no point making the the rest of the machine stiff if this part has 1/10 of the rigidity of the rest og the machine. The two vertical bracings on the front improved the stiffness but it's still not inside my requirements. The best solution to this that I have seen is Routercnc's MK4 design. However I dont have a CNC machine to build a CNC machine and I don't want to over-complicate my first build. It would be great if someone could come with input and suggestions on the design before I start ordering stuff, or it could become very expensive.
Attachment 18297
Stiffness of the Z-axis in the X direction (worst load direction) 3.9 N/um.
Attachment 18299
Stiffness; 0.85 N/um
Attachment 18298
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Re: Aluminium FEA optimalized CNC router
Have you done an analysis of resonant frequencies with the gantry and z in a variety of positions?
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Re: Aluminium FEA optimalized CNC router
Nice pictures. I would advice you to make bed analysis as well. Consider the surface you will mount the hole machine. On floor or on table. Maybe you need adjustable legs. This will probably change all calculations you made so far.
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Re: Aluminium FEA optimalized CNC router
Hi Potatomill
Some good work there using analysis to explore the design. Some comments -
Although aluminium is 3 times lighter than steel it is also 3 times less stiff. Using steel in the base assembly, where the extra weight is of no consequence and is actually very beneficial, might negate the need to add the extra triangular bracing. Especially if you can go for high wall thickness.
Don't forget that the stiffness you are aiming for (10-20 N/um) is for the WHOLE machine, from tool tip to bedplate. If you design each sub-assembly to be 10-20 N/um you will get somewhat less stiffness in total because they will behave like a set of springs in series. In other words each sub-assembly needs to be significantly stiffer than 10-20 N/um so that when added together the total stiffness is in the 10-20 N/um range.
The Z axis is always a challenge with this style of machine. Try 20-30mm thick aluminium plate and see what that does. I suspect it will not give what you want especially at 450mm long. So another option is to use a piece of RHS (steel) with say width similar to the current plate width, depth 80-100mm, and length 450mm. Then house the spindle inside with cut outs or access holes to the spindle as required.
I think the limiting factor of the design, if you really are trying to get 10-20 N/um will be the torsional stiffness of the gantry as seen by the tool tip (i.e. Z axis and gantry modelled together with load applied at tool tip).
Good luck with it all . . .
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Re: Aluminium FEA optimalized CNC router
[QUOTEmagicniner;79528]Have you done an analysis of resonant frequencies with the gantry and z in a variety of positions?[/QUOTE]
Not yet but eventually I’ll get to it. I don’t know how accurate it will be because of all the simplifications i need to do on the analysis. Frames like this have a tendency to vibrate quite a lot.
Quote:
Originally Posted by
toomast
I would advice you to make bed analysis as well. Consider the surface you will mount the hole machine. On floor or on table. Maybe you need adjustable legs. This will probably change all calculations you made so far.
I'm not completely satisfied with the base fixturing myself. I do not have the most ideal location for my machine so I have to move it twice a year. Through a door up some stairs. Hence, the plan is to put weight on it when it is in place. If I find a better location for the machine, I will change the design accordingly.
Quote:
Originally Posted by
routercnc
Although aluminium is 3 times lighter than steel it is also 3 times less stiff. Using steel in the base assembly, where the extra weight is of no consequence and is actually very beneficial, might negate the need to add the extra triangular bracing. Especially if you can go for high wall thickness.
I totally agree. Steel would be first choice if I find a good place for the machine. The Young's modulus for steel is certainly better than for aluminum.
Quote:
Originally Posted by
routercnc
Don't forget that the stiffness you are aiming for (10-20 N/um) is for the WHOLE machine, from tool tip to bedplate. If you design each sub-assembly to be 10-20 N/um you will get somewhat less stiffness in total because they will behave like a set of springs in series. In other words each sub-assembly needs to be significantly stiffer than 10-20 N/um so that when added together the total stiffness is in the 10-20 N/um range.
20 N/um is an optimistic goal. I had to do a lot of simplifications in the analysis. The worst case for the base is currently at 51 N/um and the gantry 33 N/um. As you pointed out, the twisting of the gantry, the deflection will increase with the length of the Z-axis. The base will not be as stiff either due to the fact that it's fixed to the ground in the analysis. I forgot to write it in the original post, but 500N loads where used for the base and 100N for the gantry. Adding it now. Deflection is about proportional with force, so I just multiply it up to find the stiffness in N/um.
Quote:
Originally Posted by
routercnc
The Z axis is always a challenge with this style of machine. Try 20-30mm thick aluminium plate and see what that does. I suspect it will not give what you want especially at 450mm long. So another option is to use a piece of RHS (steel) with say width similar to the current plate width, depth 80-100mm, and length 450mm. Then house the spindle inside with cut outs or access holes to the spindle as required.
I will explore this setup, and some other potential setups and post what I find out.
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3 Attachment(s)
Re: Aluminium FEA optimalized CNC router
Update on the design. I have finally managed to get sufficient stiffness in the Z cart. The solution was no surprise, maximizing second moment of area, and... steel. I also moved the Z blocks down as far as I could and placed all the Z blocks over the Y blocks. I am now planning to use a 100x200mm t=4mm square steel tube. The Z cart became twice as heavy, now 20 kg (44 lbs). However, about 20 times stiffer. The large cut on the backside is so I can get more space for the ball-screw and eventually remove the spacers for the Z blocks. I did test if the cut would compromise the design but it held up well to loads in all directions and torsional load.
Attachment 18373
Now that the Z cart is good, torsional stiffness in the gantry is the problem. I am also doing the analysis on the whole gantry with Z and Y carts. The connections between the blocks and rails is not correct. They are just bonded. I do not know of any good ways in SolidWorks to make them in an efficient way, without messing around with spring connections. Therefore, it is a gross simplification, but it should give an approximate overview of the deformation.
Attachment 18374
The image is with both gravity and a 100 N (22.4 lbs) load in the X direction, a potential worst-case load. It gives a deflection of 0.014 mm (0.55 thou). With some vibrations, joints, and the base, the deflection will be bigger. At this point, the structural frame is not the weak link any more, but ball-screws, rails, steppers, drivers, and so on. The stiffness is at 13N/um now. As I am a newbie on this, I wondered if this is a good point to settle?
The gantry, Z and Y carts weight about 40 kg (37.8 lbs) with a aluminium gantry. And 65 kg (143 lbs) with a steel gantry. So I guess steel gantry is not out of the question.
I also looked into changing the design on the gantry, by using two parallel beams and having the Y and Z cart mounted in the middle. Like Routercnc's MK4 router design. This had many advantages on the rigidity and weight distribution.
Attachment 18375
However, this would require rails on both sides of the Z cart and I cannot find any good way to prep the surface and mount them accurately. With the classic gantry design, I can use epoxy, but with the parallel beam design, the Y and Z cart becomes a problem. The design would also be a lot more complex with parallel ball-screws on Y. In addition, four rails on Z or parallel ball-screws here too. And I have enough problems to worry about already, and on a first build it's best to keep it simple.
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Re: Aluminium FEA optimalized CNC router
If you've got the Z blocks over the Y blocks how the heck are you going to do one set up??!
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Re: Aluminium FEA optimalized CNC router
Magic I suppose. I know there is a wizard over at cnczone. The setup was mainly for testing out forces and deflection, to do many iterations and test concepts I did not go trough all the details. Actually I think i'm going to use normal blocks on one side and the wider carriage on the other side. I'm going to post a image of a better assembled design soon.
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Re: Aluminium FEA optimalized CNC router
Little update on the Z and Y cartdesign, after a lot of iterations i'm now converging on a better solution for the design. However there are still changes to make and improve upon, and I hope on some feedback on my design.
http://www.cnczone.com/forums/attach...404085&thumb=1
A image of the whole thing. With the 100x200mm t=6 steel square tube in the front.
http://www.cnczone.com/forums/attach...404166&thumb=1
New setup on the stepper motor for the Z axis with a belt and pulley system. The Stepper is also mounted so it's easy to tighten the belt. It's also easy to pluck out of the machine.
The end of the ball screw it fixed with a custom double ball bearing fixture. Using 10mm thick SKF 6201 ball bearings.
http://www.cnczone.com/forums/attach...404357&thumb=1
Njhussey, after some back and fourth I managed to make space for the Mounting of the Z and Y blocks over each other.
http://www.cnczone.com/forums/attach...404679&thumb=1
Here is the square tube see-trough so it's possible to see the mounting of the spindle and the ball screw mechanism. I had to make a cut in the square tube from the top to make space for the ball screw. This did not however weaken the rigidity of the Z cartsignificantly.
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Re: Aluminium FEA optimalized CNC router
Update: Pictures is not good for viewing a design so I have placed it on GrabCAD for everyone to view in 3D. https://grabcad.com/library/z-cart-cnc-1it's currently only the Z and Y cart since i'm working on changing the gantry and the base.
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Re: Aluminium FEA optimalized CNC router
It's an interesting design and if you really want to do the Z axis that way then I would add a reinforcement panel on the front outer face of that RHS box to spread the load of the spindle out to the edges (I assume the spindle is mounted just on the front face and not sandwiched between the front and rear faces?). Say a 8-10mm thick aluminium plate as wide as the RHS and enough height to pick up on the 4 spindle mounting bolts. Otherwise the loads will go into the weaker membrane panel and not be transferred to the stiff edges. If you simplified your loading condition on the analysis this will not show up.
Same could be applied to the rails, I would add a thin strip of say 6-8mm thick steel, by 30mm wide on the inside of the RHS directly where the rails mount and screw the rail bolts right through into it.
Also in post#9, first picture, the upright bracket holding the ballnut to the Z axis is too thin. It needs to be approaching the length of the ballnut and then bolted down in 4 places. It should be a 'boss' not a 'bracket'. Also the plate it sits on is on the small side if you are trying to maximise performance. This needs a better connection to the upright Y axis plate. As drawn it will twist when loaded. Maybe a similar plate parallel to the current plate but above the ballnut would work trapping the ballnut in-between 2 plates.
Keep exploring, it's good to see something different every now and again.
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
routercnc
It's an interesting design and if you really want to do the Z axis that way then I would add a reinforcement panel on the front outer face of that RHS box to spread the load of the spindle out to the edges (I assume the spindle is mounted just on the front face and not sandwiched between the front and rear faces?). Say a 8-10mm thick aluminium plate as wide as the RHS and enough height to pick up on the 4 spindle mounting bolts. Otherwise the loads will go into the weaker membrane panel and not be transferred to the stiff edges. If you simplified your loading condition on the analysis this will not show up.
Same could be applied to the rails, I would add a thin strip of say 6-8mm thick steel, by 30mm wide on the inside of the RHS directly where the rails mount and screw the rail bolts right through into it.
Also in post#9, first picture, the upright bracket holding the ballnut to the Z axis is too thin. It needs to be approaching the length of the ballnut and then bolted down in 4 places. It should be a 'boss' not a 'bracket'. Also the plate it sits on is on the small side if you are trying to maximise performance. This needs a better connection to the upright Y axis plate. As drawn it will twist when loaded. Maybe a similar plate parallel to the current plate but above the ballnut would work trapping the ballnut in-between 2 plates.
Keep exploring, it's good to see something different every now and again.
The spindle mount is bolted from the front and the rear of the large square steel tube. However I'm not satisfied with it because the mounting of the plate can maybe drag the clamping around the spindle apart. I also need to make tramming possible.
The nice thing with the steel square tube is all the space for mounting parts. If I eventually want to add a 3:1 belt reduction on the spindle, for steel. (whisfull thinking)
Plates on the inside for the rails sounds like a good idea.
The upper ballnut connection is made of 3 layers of 10mm aluminium plates, where the lower one is bolted to the large steel tube. The grabCAD model should show it better. Or I'm misunderstanding something.
Thanks for the comments it have helped me removing a lot of weak points.
Edit: I see I forgot to add the mounting holes for the backside of the spindle attachment on the square tube.
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Re: Aluminium FEA optimalized CNC router
Now the whole thing begins to come together again. I have done some more FEA on the whole frame. I will just add that they are approximations and gives a rough overview. Joints and mounting points will add to the deflections.
Attachment 18408
Base:
I did some test with and without the side supports. The side supports make the base a lot more rigid. However, without the side support the deflection on the base is still insignificant compared to the gantry and the y and z carts. I also looked at how steel would increase the rigidity, but since the deflection on the base already was insignificant on the total frame, the increased stiffness from the steel was very small on the whole frame. The base is about 57kg with aluminum and 105kg with steel.
Attachment 18407
Gantry:
The gantry have a lot to say on the stiffness of the frame especially torsion that add to deflection on loads in the x axis. The gantry is changed from a frame with a lot of 60x60mm square tubes to a single 300x200mm t=6 rectangular tube. The stiffness of the new setup is about the same, but it makes the assembly a lot easier. Which means there is less areas to make mistakes the rigidity of the machine will suffer from. I had to go for steel on the gantry to get it rigid enough, an aluminum rectangular tube was just not enough. Casting aluminum could be possible, but that will again make it more complex and prone to errors. The gantry is still movable on its own, but it is now at 50kg. :suspicion: The Y and Z cart is at 20kg so in total the gantry and Y and Z cart will be 70kg.
The design on GrabCad is now updated https://grabcad.com/library/z-and-y-cart-gantry-cnc-1. However, the ball screws for moving the gantry is not finished yet. And I see that mounting of the rails for the Y cart makes it impossible to attach the Y cart so I have to find a solution for that. Moreover, it would be great if someone have a good suggestion.
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Re: Aluminium FEA optimalized CNC router
Given that the additional cost and effort is low I'd add the side supports anyway as there may be a significant reduction in resonance under circumstances for which you have not calculated.
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
magicniner
Given that the additional cost and effort is low I'd add the side supports anyway as there may be a significant reduction in resonance under circumstances for which you have not calculated.
Indeed, that's why I will probably build them anyway, but it can also be easily added later. The only minus is the added with, if I can get it trough a door on wheels whitout removing the gantry and tipping it on the side it would be nice. Else than that it is only positive with the added rigidity for unforseen deflections. Hovewer the base is already more than strong enough, it's the torsion on the gantry that is the weak point.
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Re: Aluminium FEA optimalized CNC router
I'm currently considering making a stationary gantry design. Since the weight of the gantry pluss the z and y cart comes inn at 80kg (mostly in steel).
The cons will be;
-Longer machine
-Longer rails
-Potensial for sag in the bed
Pros
-Less weight to move for the steppers
-Simpler design
-Less twist on the z axis, the largest factor for displacement
The reason i'm posting this is because it probably a lot more pros and cons than I can come up with, that I hope someone here will add.
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Re: Aluminium FEA optimalized CNC router
So I have been working on redesigning the whole machine. I'm currently going for a stationary gantry design.
Attachment 18718
Due to the fixed gantry design the heaviest moving part is now the base plate with 30kg. I'm going to use 20mm HIWIN profile rails on all axis.
There will be one lead screw on each axis, no need for two on the X any more due to the stationary gantry. Here i'm going to use 1605 ball-screws. To drive the axis i'm currently looking at using servos in the 200-400W range. There is not the same amount of information on servos av steppers so I hope someone here have some knowledge on servos. Seems like JMC produce the cheapest servos and drives, but I cant find a lot of data on them. If there servos from JMC are good enough i'm probably going to use them. BST automation also seems to have a ok selection on servos, but again there is little documentation to find.
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
PotatoMill
BST automation also seems to have a ok selection on servos, but again there is little documentation to find.
If you send them a msg Fred will be more than happy to help and send you what you need.
.Me
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
PotatoMill
It looks like you have the rails on the base and the carriages moving on the X-axis.
If you have the carriages fixed on the base and the rails moving under the X-axis you can have maximum support and rigidity where you need it most at all times.
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Re: Aluminium FEA optimalized CNC router
I can give some info about that. I have one 60ASM200 at home. My computer is not enough fast for this resolution, so that is why it looks slow on a video. The electric gear ratio is 1:1. https://www.youtube.com/watch?v=qyrEdBIpqx8
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
remrendes
I can give some info about that. I have one 60ASM200 at home. My computer is not enough fast for this resolution, so that is why it looks slow on a video. The electric gear ratio is 1:1.
https://www.youtube.com/watch?v=qyrEdBIpqx8
Go on then, Giz a Clue?
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Re: Aluminium FEA optimalized CNC router
A square tubes looks not enough strong for me for aluminium machining.
I'm working on this frame for alu, with a smaller motors than what you want.
Attachment 18722
You should move the X ballscrow to lower. It is better between the 2 rails.
Everything looks welded. How can you do the end machining for a rails and others?
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Re: Aluminium FEA optimalized CNC router
Info about what specifically?
I can't see who's post you are addressing and though it's obvious to you it's not obvious to me :-(
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Re: Aluminium FEA optimalized CNC router
The design is kinda crude, it was a fast iteration. I'll probably get some time in the weekend to upgrade it so the details is more understandable. The i'm going to add end plates to the large gantry square tube. Most of the machine will be welded. I have planned to bolt the gantry and base together at the bottom of the gantry legs. I guess I need to remove the aluminium part in the title of the post sinse it's mostly steel now.
Quote:
Originally Posted by Lee Roberts
If you send them a msg Fred will be more than happy to help and send you what you need.
Thanks for the tips, seems like Fred is a helpful guy.
Quote:
Originally Posted by
magicniner
It looks like you have the rails on the base and the carriages moving on the X-axis.
If you have the carriages fixed on the base and the rails moving under the X-axis you can have maximum support and rigidity where you need it most at all times.
I agree, I changed it back and forth several times. It became a compromise. Rails on the base would make sure the support is maksimum and equal at all times. However the moving base would be longer and the leverage from the longer base would put more stress on the machine. The weight of the moving part would also be higher.
Quote:
Originally Posted by
remrendes
I can give some info about that. I have one 60ASM200 at home. My computer is not enough fast for this resolution, so that is why it looks slow on a video. The electric gear ratio is 1:1.https://www.youtube.com/watch?v=qyrEdBIpqx8
Nice video, you got any info in addition?
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
magicniner
Info about what specifically?
I can't see who's post you are addressing and though it's obvious to you it's not obvious to me :-(
Sorry, 60ASM200 is a JMC servo motor, what I mean.
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
PotatoMill
Nice video, you got any info in addition?
I have eveything :) I can give a contact number as well, I have seen a factory in China. They are pretty good.
If I will not forget, I'm going to upload a training video what I have from them.
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Re: Aluminium FEA optimalized CNC router
The cost of servos is going to be quite high, so i'll probably for closed loop steppers instead. However the ClearPath servos seems tempting. Is there any good reason to use servos instead of closed loop steppers?
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
PotatoMill
The cost of servos is going to be quite high, so i'll probably for closed loop steppers instead. However the ClearPath servos seems tempting. Is there any good reason to use servos instead of closed loop steppers?
Closed loop steppers don't have the speed or torque capabilities of servos and are sold as an 'economical' alternative. The only good reason to use closed loop steppers is because they are cheaper.
Some cheap servos like the JMC can be similar price to most closed loop steppers, it'll be interesting to know if anyone has tested how their performances compare.
Cheers,
Fenza
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
PotatoMill
The cost of servos is going to be quite high, so i'll probably for closed loop steppers instead. However the ClearPath servos seems tempting. Is there any good reason to use servos instead of closed loop steppers?
Both have a feedback to driver, so both are better than a normal steppers.
A cost of the servos is higher than what you think. E.g. you have to reduce the rpm, with 1:2 - 1:3 transmission. 1x zero backlash pulley is approx £30-40, one belt can be £15-20 and you need 3 set. With steppers, you just need a coupling.
Unfortunately I started with servos, but I could get a cheap set from China.
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Re: Aluminium FEA optimalized CNC router
Thanks for the quick response Fenza and Remrendes
According to a quick estimate I did I dont think i'm going to need any more torque than what these closed loop steppers deliver; http://www.aliexpress.com/item/new-o...a-82b3fb4b4813
Estimates done with
-40kg weight of moving part
-130N force of cutter (excessive)
-20N friction
-85% efficiency
-10 m/s^2 acceleration (more than I think i'll need, but I haven built any CNC machines before so i'm not certain on this.)
-5mm lead
Using T = (F*l)/(2*PI*n) where F is total force, l is lead per revolution, n efficiency
I get 0.44N well within
However I do know that theory and experience dont always match up. And in real life there could be some factor that make the estimate wrong.
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
PotatoMill
Thanks for the quick response Fenza and Remrendes
According to a quick estimate I did I dont think i'm going to need any more torque than what these closed loop steppers deliver;
http://www.aliexpress.com/item/new-o...a-82b3fb4b4813
Estimates done with
-40kg weight of moving part
-130N force of cutter (excessive)
-20N friction
-85% efficiency
-10 m/s^2 acceleration (more than I think i'll need, but I haven built any CNC machines before so i'm not certain on this.)
-5mm lead
Using T = (F*l)/(2*PI*n) where F is total force, l is lead per revolution, n efficiency
I get 0.44N well within
However I do know that theory and experience dont always match up. And in real life there could be some factor that make the estimate wrong.
Hi PotatoMill your math certainly is correct but it doesn't account for the full picture. I use Kollmorgen MOTIONEERING to calculate more precisely what kind of motors are required, it's a little tricky to understand in the beginning but sticking with it pays off massively! http://www.kollmorgen.com/en-us/serv...eering-online/ here's the link to their site. I use their older application at the bottom of that page, it looks like they have a new online tool available now.
Kollmorgen have a huge range of motors available and the MOTIONEERING app helps point you to which is suited for your machine, I just use the data from that motor to base my search for a cheap servo / stepper system off of.
Also always remember that steppers holding torque is not the same as a servo rated/max torque.
A good rule of thumb that I use (though I'm not entirely sure it's correct) is that a 3Nm stepper is roughly equal in power to a 100W Servo.
Hope this helps!
Fenza
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
PotatoMill
Estimates done with
-40kg weight of moving part
-130N force of cutter (excessive)
-20N friction
-85% efficiency
-10 m/s^2 acceleration (more than I think i'll need, but I haven built any CNC machines before so i'm not certain on this.)
-5mm lead
With 5mm lead is not the best ballscrew for you. You shoud use the motors up to 500rpm. Under this, you nearly can get a full holding torque.
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Re: Aluminium FEA optimalized CNC router
It would probably be best to make a 3:1 gearing to utilize the holding torque best. Or is it possible to get cheap ballscrews with shorter than 5mm lead?
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
PotatoMill
It would probably be best to make a 3:1 gearing to utilize the holding torque best. Or is it possible to get cheap ballscrews with shorter than 5mm lead?
I would go for 10mm pitch and direct drive.
On 500rpm it is 5000mm/min, more than enough.
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
Fenza
Hi PotatoMill your math certainly is correct but it doesn't account for the full picture. I use Kollmorgen MOTIONEERING to calculate more precisely what kind of motors are required, it's a little tricky to understand in the beginning but sticking with it pays off massively!
http://www.kollmorgen.com/en-us/serv...eering-online/ here's the link to their site. I use their older application at the bottom of that page, it looks like they have a new online tool available now.
Kollmorgen have a huge range of motors available and the MOTIONEERING app helps point you to which is suited for your machine, I just use the data from that motor to base my search for a cheap servo / stepper system off of.
Also always remember that steppers holding torque is not the same as a servo rated/max torque.
A good rule of thumb that I use (though I'm not entirely sure it's correct) is that a 3Nm stepper is roughly equal in power to a 100W Servo.
Hope this helps!
Fenza
Great tool, very helpful. I'm trying both the new and old now, the old one seems better actually.
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
remrendes
I would go for 10mm pitch and direct drive.
On 500rpm it is 5000mm/min, more than enough.
Wouldn't I want shorter pitch? If not I would not get close to the corner speed at all. And waste a lot of usable torque.
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1 Attachment(s)
Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
PotatoMill
Wouldn't I want shorter pitch? If not I would not get close to the corner speed at all. And waste a lot of usable torque.
With steppers? No, not really.
What do you mean with a corner speed?
Here you can see a torque curve for both. You can calculate with a 0-500rpm range.
Attachment 18743
Unfortuantely it is Hungarian, but here you can see my calculation for my X axis with servo. This is the optimal for a dynamics, but I chosen 2.5:1.
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Re: Aluminium FEA optimalized CNC router
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
PotatoMill
Yes, it is on the speed/torque curve, where the motor starts to loose his torque. Approx 4-600rpm on a cheap steppers.
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Re: Aluminium FEA optimalized CNC router
Hi PotatoMill, I see you specced 10m/s^2 acceleration. Now I'm not too experienced with routers and steppers (Mills and Servos is more my thing) but 1g is kind of a lot! I did a quick calculation and a 20mm ball screw 1,200mm length 5mm pitch with 40kg load will require over 3Nm of torque at the shaft to accelerate all the moving parts at 10m/s^2
Cutting forces are only small but the force required to overcome inertia and accelerate a 40kg load is great!
I believe 2.5m/s^2 would be a good target to try and aim for, though It would be nice if someone experienced with steppers and routers could chime in and advise. I believe 50in/s^2 is considered not too shabby in Mach3 which would be 1.27m/s^2
Hope this helps! That Kollmorgen app really is a great tool once you get used to it :beer:
Fenza