X axis wobble in corexy printer
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@mrehorstdmd I had an idea today how you could verify whether the pulleys are off-center: connect two pulleys with different teeth with a closed belt with good tension and turn them. The force needed should be even for full rotations if they are centered correctly. Depending on after how many rotations the force changes you can see which pulley is off-center also.
In my experience the belts are very sensible against length variations. That's why flexible belt tesioners are used sometimes: they hide construction inaccuracies like off center pulleys. This strikes back with bad prints however, because stepper-belt movement is not in sync.
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@JoergS5 When I watch the machine running, I can see one of the belts moving laterally as it comes off the drive pulley. The other one is a lot better.
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These LDO pulleys are supposed to be of high quality and a got fit for Gates belts.
https://www.printedsolid.com/products/ldo-2gt-pulley-with-5mm-bore
I have them on my printer and they do 'work' but I can't quantify it.
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@zapta While the reviews look good, I need 20 tooth, 9 mm wide... Thanks!
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see the voron 2.4 bom
https://vorondesign.com/sourcing_guide?model=V2.4
they recommend these with the gates belts.
https://de.aliexpress.com/item/32650675929.html -
One of the downsides of CoreXY and other flying gantry designs (my first original design was a flying gantry), is that the belt configuration adds a whole bunch of tolerance stacking, magnifying any issues with cheap pulleys.
That original design... couldn't print straight lines in Y, because I used cheap pulleys and the belt configuration multiplied the error in the X pulleys. As it moved in Y you could literally see the head moving back and forth in X.
Hmm... Might be finally time to build that ballscrew based machine I'm been meaning to for ages.
I'm curious to see the results of better quality pulleys.
And I'm curious, is there any pre-load on your linear bearings? -
Decent belts & pulleys help. Retention of the pulleys in double shear and using shafts properly retained instead of bolts all add up to one thing.
A properly executed design, built properly.
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@mrehorstdmd said in X axis wobble in corexy printer:
I need 20 tooth, 9 mm wide...
Are you CERTAIN your motor shaft is not bent? Throw a test indicator on there
I am just south of you and have some 9mm pulleys or what i think are good quality, I think that are 20 tooth. If you want to borrow, DM me. USPS is cheap and fast across the border.
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I had a similar experience and came to a similar conclusion - I've used cheap pulleys on a much smaller corexy I had fabricobbled, but on my large machine with 9mm belts they just weren't cutting it. Had to bite the bullet and purchase genuine gates pulleys, and improved it quite a bit! There are some videos that show how bad the wobble was from the inferior pulleys, it was actuating my y-limit switch!
https://www.lukeslab.online/blog/a-problem-with-idlers-solved-with-gates -
@Luke-sLaboratory I use stacked F608 bearings for idlers in my printer- they turn very smoothly and their concentricity seems to be very good. Their 22mm diameter means I can let the toothed side of the belt ride on them without generating any artifacts in the prints. The bearings and the 8mm bolts that serve as axles are quite heavy. I expect them to last many years.
I used some cheapo 3D printer pulleys (3mm bore) in my first sand table build and found them to be junk. They wore out very quickly. A more recent version of the table uses stacked F625 bearings (5mm bore)- much better than the 3D printer pulleys.
@sinned6915 No, I am not certain the motor shafts aren't bent- I'll have to check them. One of the cheapo servomotors I used in the sand table has a bent shaft, so I suppose a stepper could, too. I originally designed the servomotor mounts with bearings and found that with that motor, the extra bearing made it run noisy, so I took the bearings out of the motor mounts.
@theruttmeister No, no preload in the linear guides.
