Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 12:21PM |
Registered: 9 years ago Posts: 344 |
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 01:11PM |
Admin Registered: 11 years ago Posts: 1,063 |
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cristian
I wonder why in most printers GT2 belts are used for X and Y axes, which give a quite "low" resolution, while so much care is taken for Z axis. A typical GT2 pulley has a diameter of 12 mm, which gives about 40mm for a full turn. If we ignore microstepping, this corresponds (again: usually) to 200 steps / 40mm = 5 steps per millimeter for X and Y axes. If for Z a threaded rod with 6mm diameter is used (metric thread), this gives about 200 steps per turn = 200 steps per millimeter along Z.
So:
X/Y: 5 steps per millimeter ==> 1 step is 0.2 mm = 200 micron
Z: 200 steps per millimeter ==> 1 step is 0.005 mm = 5 micron
Does this make sense in terms of control on printing quality?
If we ignore microstepping (for example if microsteps are not too precise), it seems to me that the X/Y resolution is definitely too low unless one is printing with 0.8mm or bigger nozzle. On the other hand, Z resolution is far too high unless one wants to print at very very low layer height. If we consider microstepping, then Z resolution is just wasted.
Moreover, belts have quite big teeth that may leave some traces on the surfaces of the prints, since I would expect that the pitch of a (tightened) belt is different from the pitch of the pulley by some microns at least.
What do you think?
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belts have quite big teeth that may leave some traces on the surfaces of the prints
have you got any evidence of this occurring ?
i think you are overthinking it .....
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 01:20PM |
Registered: 9 years ago Posts: 1,873 |
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 01:31PM |
Registered: 10 years ago Posts: 14,672 |
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JamesK
The Z axis has very different requirements to X & Y for most printer designs as it usually carries a lot more weight and performs more limited movements. Lead screws make sense for Z, while the lighter & faster belt drives make sense for X & Y. Not that you couldn't use lead screws everywhere, but you'd have to spend a lot more to get the same dynamics.
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 01:36PM |
Registered: 9 years ago Posts: 1,873 |
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dc42
On a delta printer, the Z axis drive relies on belts too. I have found this quite adequate down to layers heights of 0.1mm. I haven't tried lower.
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 01:37PM |
Admin Registered: 16 years ago Posts: 13,891 |
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 01:44PM |
Registered: 9 years ago Posts: 396 |
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 01:45PM |
Registered: 11 years ago Posts: 335 |
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 01:46PM |
Registered: 9 years ago Posts: 344 |
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thejollygrimreaper
have you got any evidence of this occurring ?Quote
belts have quite big teeth that may leave some traces on the surfaces of the prints
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JamesK
The Z axis has very different requirements to X & Y for most printer designs as it usually carries a lot more weight and performs more limited movements. Lead screws make sense for Z, while the lighter & faster belt drives make sense for X & Y.
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dc42
On a delta printer, the Z axis drive relies on belts too. I have found this quite adequate down to layers heights of 0.1mm. I haven't tried lower.
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 01:58PM |
Registered: 9 years ago Posts: 344 |
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VDX
... belt drives are been used mostly for higher possible speeds than with spindles.
As the Z-axe can be much slower and the steppers with spindles can withstand the gravity with motors off, this is the most practical solution for the standard machines ...
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 01:59PM |
Registered: 9 years ago Posts: 1,873 |
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The difference in resolution between Z and X/Y is about 40 times. I agree that Z is different from X and Y, but not "40 times" different. The weight of my bed is more than 0.5kg and it relies on a belt to move horizontally. Please show me a printer that has a bed lighter than 0.5kg and something to move along Z that weights 40 times 0.5 kg = 20 kg.
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 02:13PM |
Registered: 9 years ago Posts: 344 |
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JamesK
The weight of the bed isn't supported by the belts, it's supported by the smooth rods (or other linear bearings). On the Z axis the weight bears directly on the movement system, and in many designs is transferred directly to the stepper motors. None of the weight on the Z axis is supported by the smooth rods. It's this primary factor that makes the difference in gearing between XY and Z appropriate. I guess this also factors into why Delta style printers aim to keep the moving mass as light as possible, along with the speed benefits that go hand in hand and are normally given as primary motivation.
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JamesK
Another factor is that for Z micro-stepping is used for smoothness of motion, but layer heights are recommend to be multiples of the full step distance in order to avoid vertical banding. So for this case your suggestion of ignoring micro-stepping is entirely accurate, and a lower physical gearing is needed to maintain precision.
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 02:21PM |
Registered: 9 years ago Posts: 1,873 |
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 02:26PM |
Registered: 10 years ago Posts: 14,672 |
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JamesK
I think most Deltas use ABL, not sure how that plays into the situation.
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 02:45PM |
Registered: 9 years ago Posts: 344 |
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JamesK
Um, so I don't want to seem argumentative
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JamesK
but a 1G acceleration equates to 9800mm/s2 - is that considered normal printing speed? I confess to a lack of knowledge, but that sounds on the high side to me.
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 03:33PM |
Registered: 10 years ago Posts: 869 |
Cost, speed, resolution. Pick 2. Belts enable a cheap stepper motor to move things faster. The same motor enables a lead screw to move things with better resolution. If you want to move things fast and with higher resolution, you'll need something better than a standard NEMA 17 motor as a starting point. Yes there's a big difference in accuracy between belt driven X and Y and lead-screw driven Z. But it works, and for a vast majority, is good enough. Z doesn't need to move fast, so going overboard with resolution is better than not enough. You could replace all three axis with a more custom screw with a larger lead distance, but then your costs go up considerably as compared to standard threaded rod available in many hardware stores.Quote
cristian
If we ignore microstepping (for example if microsteps are not too precise), it seems to me that the X/Y resolution is definitely too low unless one is printing with 0.8mm or bigger nozzle. On the other hand, Z resolution is far too high unless one wants to print at very very low layer height. If we consider microstepping, then Z resolution is just wasted.
Get a belt and pulley that's made for bidirectional positioning and it shouldn't be an issue.Quote
Moreover, belts have quite big teeth that may leave some traces on the surfaces of the prints, since I would expect that the pitch of a (tightened) belt is different from the pitch of the pulley by some microns at least.
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 03:47PM |
Registered: 9 years ago Posts: 344 |
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cdru
Cost, speed, resolution. Pick 2. Belts enable a cheap stepper motor to move things faster. The same motor enables a lead screw to move things with better resolution. If you want to move things fast and with higher resolution, you'll need something better than a standard NEMA 17 motor as a starting point. Yes there's a big difference in accuracy between belt driven X and Y and lead-screw driven Z. But it works, and for a vast majority, is good enough. Z doesn't need to move fast, so going overboard with resolution is better than not enough.
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cdru
You could replace all three axis with a more custom screw with a larger lead distance, but then your costs go up considerably as compared to standard threaded rod available in many hardware stores.
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cdru
Get a belt and pulley that's made for bidirectional positioning and it shouldn't be an issue.
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 03:55PM |
Registered: 9 years ago Posts: 1,873 |
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 03:58PM |
Registered: 9 years ago Posts: 344 |
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JamesK
Mark's (digital dentist) build uses a ball screw on Y with very impressive results. He posted a writeup [www.instructables.com]
If you can't glean what you want to know from there I'm sure he'd be happy to answer questions.
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 05:31PM |
Admin Registered: 11 years ago Posts: 1,063 |
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cristian
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thejollygrimreaper
have you got any evidence of this occurring ?Quote
belts have quite big teeth that may leave some traces on the surfaces of the prints
I think I do. I have seen vertical stripes on many printed objects with glossy surface from different printers and I cannot find any other reason for their existence. I cannot quantify the stripes in terms of microns, though. For sure they do not affect the printed objects in terms of functionality, but they do exist, and quality is not necessarily just "being functional" mechanically.
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 05:37PM |
Admin Registered: 16 years ago Posts: 13,891 |
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 05:45PM |
Registered: 9 years ago Posts: 344 |
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thejollygrimreaper
those vertical stripes/ridges are actually the belts vibrating/ringing on a direction change, (eg on corners and such, ) , it's a side effect of a lot of the high speed printing people seem to like to do these days however the solution i found is rather simple and doesn't involve spending days tuning acceleration values , you just slow down the perimeter speed , on my printer i go down to 15mm/sec for the perimeters and the effect is all but eliminated.
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VDX
... vertical stripes on the surface, corresponding with teeth spacing, are caused mostly by the belts, running around smooth bearings - the tension of the belt changes with the count of teeth or gaps pressing on the bearings.
To avoid this, you'll need pulleys with the correct form ...
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 06:26PM |
Registered: 9 years ago Posts: 1,873 |
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dc42
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JamesK
I think most Deltas use ABL, not sure how that plays into the situation.
Best practice on delta machines is to use the Z probe to perform delta calibration, but not to use ABL. People using ABL on deltas generally haven't calibrated them properly.
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 06:27PM |
Admin Registered: 11 years ago Posts: 1,063 |
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cristian
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thejollygrimreaper
those vertical stripes/ridges are actually the belts vibrating/ringing on a direction change, (eg on corners and such, ) , it's a side effect of a lot of the high speed printing people seem to like to do these days however the solution i found is rather simple and doesn't involve spending days tuning acceleration values , you just slow down the perimeter speed , on my printer i go down to 15mm/sec for the perimeters and the effect is all but eliminated.
I don't think we are talking about the same stripes. Those that come from vibration on a direction change follow the corners of the printed object, and obey some sort of exponential attenuation the same way spring oscillations do. The stripes I am talking about do not depend on that, they are present all over the object and have no attenuation. Sorry not to be able to provide a picture, I will take one if I have the chance.
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VDX
... vertical stripes on the surface, corresponding with teeth spacing, are caused mostly by the belts, running around smooth bearings - the tension of the belt changes with the count of teeth or gaps pressing on the bearings.
To avoid this, you'll need pulleys with the correct form ...
Thank you for the tip, I cannot confirm or disprove it yet but I will pay attention to it the next time to see if that is actually the source of those stripes.
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 07:02PM |
Registered: 11 years ago Posts: 5,780 |
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 07:04PM |
Registered: 9 years ago Posts: 977 |
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VDX
... vertical stripes on the surface, corresponding with teeth spacing, are caused mostly by the belts, running around smooth bearings - the tension of the belt changes with the count of teeth or gaps pressing on the bearings.
To avoid this, you'll need pulleys with the correct form ...
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 07:24PM |
Admin Registered: 16 years ago Posts: 13,891 |
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 07:43PM |
Registered: 9 years ago Posts: 1,873 |
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the center distance from the table changes with every tooth or gap ... this will be the same, but with much lower effect, when you bend a belt around a smooth bearing/cylinder and move it around
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 07:51PM |
Registered: 9 years ago Posts: 344 |
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thejollygrimreaper
what type of belt are you using? and on what size pulleys?
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the_digital_dentist
I've looked at all the flutes under the microscope and they all look the same in terms of positional accuracy and uniformity of layer thickness.
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the_digital_dentist
I have printed down to 50 um layers with the 0.4mm nozzle, but extruder calibration was off a little and the prints looked a little blobby. I have a 0.25mm nozzle that I'll put on the machine one of these days and then I'll calibrate the extruder at 20 or 50 um and try a small print.
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AndrewBCN
Yes, GT2 (and I suppose some other types, but I have only used GT2) belts are more than precise enough when used to provide linear motion along the X and Y axis in a Prusa i3-style printer, or along the three X, Y and Z towers in a linear delta, at least as far as current FDM technology is concerned (I mean, with current layer thicknesses and nozzle diameters). This can be demonstrated both by calculating the theoretical precision of belt drives, but also by empirical observation of printed objects on printers that use belt systems (the calculations in the OP's first post are missing microstepping considerations as already remarked, leading to incorrect conclusions).
There is strictly nothing to gain (in terms of resolution) by using more expensive linear drive mechanisms.
Re: Resolution along X and Y vs Z: are belts precise enough? May 29, 2015 08:03PM |
Registered: 9 years ago Posts: 977 |