New printer design with new 'twist' for XY on Z March 03, 2018 05:51PM |
Registered: 7 years ago Posts: 207 |
Re: New printer design with new 'twist' for XY on Z March 04, 2018 03:05AM |
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Re: New printer design with new 'twist' for XY on Z March 04, 2018 11:26AM |
Registered: 7 years ago Posts: 207 |
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o_lampe
Interesting!
I'd definitely add a fixed top frame with cross braces, because the stability when the printhead is down, is pretty low.
Re: New printer design with new 'twist' for XY on Z March 04, 2018 08:21PM |
Registered: 12 years ago Posts: 335 |
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klcjr89
Are you saying to add a 1/2" top plate and connect this top plate to the bottom plate with other plates/diagonal pieces?
Also, do you see any problems with print layer registration or the XY plane moving around while the Z axis moves up? The holes will be cnc machined to ensure perpendicularity and correct spacing for orthogonality.
I hope the minor deviation in the linear shaft and leadscrew straightness won't be an issue? The 500mm leadscrew has a runout spec of 160 microns or less, and the 500mm linear shaft straightness spec is 50 microns or less.
Re: New printer design with new 'twist' for XY on Z March 04, 2018 08:23PM |
Registered: 7 years ago Posts: 207 |
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691175002
You need some way to keep the shafts vertical, pressing them in wont provide enough resistance to side loads and your printer will fold like a parallelogram.
The design is very space efficient, but supporting your linear shafts on only one side will cost a lot of rigidity. TBH the math doesn't look great even with 20mm shafts.
Re: New printer design with new 'twist' for XY on Z March 04, 2018 08:53PM |
Registered: 12 years ago Posts: 335 |
Re: New printer design with new 'twist' for XY on Z March 04, 2018 08:59PM |
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691175002
I edited my post with a few more details. The side-loads on a 3d printer might be small, but you are still looking at maybe 200-400g of acceleration depending on the speed and extruder being used.
If you put that load on the very end of a 500mm rod that is only being held by a tiny section on one end it will still bend quite a bit. For example here is an extremely rough FEA where I modeled the whole assembly as a solid block of steel and it moves 0.05mm when 200g of force is applied. Its not awful, but the simulation is probably 2-4 times more rigid than your actual build will be and that kind of deflection will be visible.
The bigger problem IMO is that if you leave the rods unsupported and someone bumps into them you are essentially applying half a meter of leverage to a very small hole in a piece of cast aluminum. I'd guess 2Kg at the top of the rod could permanently damage the alignment of the printer.
Again, not awful, but not really something I'd want to risk.
Re: New printer design with new 'twist' for XY on Z March 04, 2018 09:35PM |
Registered: 8 years ago Posts: 28 |
Re: New printer design with new 'twist' for XY on Z March 04, 2018 09:38PM |
Registered: 7 years ago Posts: 207 |
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orea
Looks interesting, maybe consider a frame with linear rails for stability.
Re: New printer design with new 'twist' for XY on Z March 04, 2018 10:12PM |
Registered: 12 years ago Posts: 5,794 |
Re: New printer design with new 'twist' for XY on Z March 04, 2018 10:14PM |
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the_digital_dentist
The planer doesn't have to worry about stacking 200 um layers of plastic on each other with a few 10s of microns accuracy and precision, and its Z movement range is just a few cm.
Re: New printer design with new 'twist' for XY on Z March 04, 2018 10:30PM |
Registered: 12 years ago Posts: 5,794 |
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klcjr89
Is that only info you came to provide here?
Re: New printer design with new 'twist' for XY on Z March 04, 2018 10:32PM |
Registered: 7 years ago Posts: 207 |
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the_digital_dentist
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klcjr89
Is that only info you came to provide here?
Sometimes pointing out the obvious is the best info to provide.
Re: New printer design with new 'twist' for XY on Z March 04, 2018 11:12PM |
Registered: 7 years ago Posts: 207 |
Re: New printer design with new 'twist' for XY on Z March 05, 2018 03:18AM |
Registered: 9 years ago Posts: 5,232 |
Re: New printer design with new 'twist' for XY on Z March 05, 2018 10:03AM |
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Re: New printer design with new 'twist' for XY on Z March 05, 2018 12:25PM |
Registered: 7 years ago Posts: 207 |
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o_lampe
IMHO the nut-bearing mount should be swimming somehow.
Re: New printer design with new 'twist' for XY on Z March 05, 2018 01:23PM |
Registered: 12 years ago Posts: 335 |
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klcjr89
Your post and edited post are helpful! When you mentioned the 22mm diameter leadscrew as 'doing almost nothing', do you mean that it's just oversized for no purpose other than visually matching the size of the linear shafts?
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If the ballnut's OD is 40mm, I could solve this with just using a 42mm ID bushing, correct?
Re: New printer design with new 'twist' for XY on Z March 05, 2018 01:44PM |
Registered: 7 years ago Posts: 207 |
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691175002
The underlying problem is that you need three points to define a plane. Using two leadscrews and two linear shafts is awkward because you are overconstrained in some ways but underconstrained in others. I'd consider doing this with three or four Chinese 2005 ballscrews and no linear shafts, but using ballscrews as linear guides is rather experimental.
Re: New printer design with new 'twist' for XY on Z March 05, 2018 03:05PM |
Registered: 12 years ago Posts: 335 |
Re: New printer design with new 'twist' for XY on Z March 05, 2018 03:14PM |
Registered: 7 years ago Posts: 207 |
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691175002
Three screws will be easier to align than four screws but I agree that it would look a little weird. I would probably go with four screws myself.
You can find standard belts in 2m+ lengths if you go up to the ~3mm pitches, but I wouldn't immediately discard the idea of using four steppers. The steppers will only be moving in Z so their weight is essentially irrelevant. Its the moving mass on the gantry or carriage that needs to be minimized.
The primary tradeoff of a seperate stepper for each screw is that you need to keep them synchronized. Automatic leveling will take care of minor misalignments, but if the screws diverge too much the axis could bind.
I'd probably make a call to go the easy route here and rely on automatic bed probing/leveling. Ballscrews can backdrive so it should actually be impossible for the axis to bind. (The screws will return to a relaxed state when unpowered.)
Re: New printer design with new 'twist' for XY on Z March 05, 2018 03:37PM |
Registered: 7 years ago Posts: 249 |
Re: New printer design with new 'twist' for XY on Z March 05, 2018 03:58PM |
Registered: 12 years ago Posts: 5,794 |
Re: New printer design with new 'twist' for XY on Z March 05, 2018 04:05PM |
Registered: 7 years ago Posts: 207 |
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the_digital_dentist
If you spend the money on the controller expansion board, the extra drivers, the cables, the sensors, and the beefier power supply to handle four Z axis motors, you'll end up with a printer that levels the bed automatically and gets that first layer to stick... until something fails, and then you won't be able to print at all.
OTOH, if you use some of the money you would have spent on all that stuff and make a rigid frame for the printer, and drive all the Z axis screws using a single motor, after initial setup the bed will stay level (you won't need autoleveling) and there will be less stuff to fail - i.e. the machine will be more reliable.
If your goal is to make awesome youtube videos, go with the autoleveling. If your goal is to make an awesomely reliable printer, go the other way.
Have you ever sat at a table that has four feet/legs in a cafe or restaurant? Have you ever had to put a piece of cardboard under the table's foot because the table kept rocking? That's what will happen if you use 4 screws to drive the Z axis. 3 points define a plane. Using 3 screws under a planar surface is inherently stable. Adding a fourth adds instability.
Re: New printer design with new 'twist' for XY on Z March 05, 2018 04:22PM |
Registered: 10 years ago Posts: 14,685 |
Re: New printer design with new 'twist' for XY on Z March 05, 2018 04:22PM |
Registered: 12 years ago Posts: 335 |
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klcjr89
If you had the choice, would you go with a single stepper and a closed loop belt? The idea to initially 'level' each corner at first is to lower the XY plate down to where each corner references the bottom Mic-6 plate (use a 123 block or similar), and then at this moment you tighten each pulley to the ballnut with a set screw, keeping synchronization.
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klcjr89
I can't wrap my head around how a four stepper motor Z with autoleveling would work.
Re: New printer design with new 'twist' for XY on Z March 05, 2018 04:34PM |
Registered: 7 years ago Posts: 207 |
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691175002
As I mentioned before, using ballscrews as linear guides is discouraged, but the datasheets make it seem pretty plausible. Its entirely possible that screws might be smoother than the Chinese LMU parts. [imgur.com]
Re: New printer design with new 'twist' for XY on Z March 05, 2018 05:42PM |
Registered: 12 years ago Posts: 335 |
Re: New printer design with new 'twist' for XY on Z March 05, 2018 05:47PM |
Registered: 7 years ago Posts: 207 |
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691175002
Virtually any ballscrew should be fine here. I remember the Chinese rolled screws being roughly a third of the price of Misumi's C10 screws, and have found them to be acceptable, so you could give that some consideration.
Appropriate screw diameter depends on how they are being supported. The weak point is likely to be the connection between the base and the screw, so unless you have a good plan for that interface larger screws won't help much.
I'm not a huge fan of pressing the screws into 1/2" plate because of the leverage it creates. I would probably be looking at putting a huge steel washer/shim on one or both sides of the plate to distribute the load, and machining the end of the ballscrew so that it clamps down on the plate + washer/shim.
[us.misumi-ec.com]
Re: New printer design with new 'twist' for XY on Z March 05, 2018 07:45PM |
Registered: 12 years ago Posts: 5,794 |
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klcjr89
In the reliable case of using three synchronized ballscrews with one stepper motor, would you recommend the fourth corner being a 25mm ground linear shaft?