#X / Y axis backlash or hysteresis (oval circles problem), tried more than 10 "fixes" without success

24 messages · Page 1 of 1 (latest)

quick rapids
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Recently I've been experiencing a oval circles problem, with the ovals at 45 degree angles.
That's how it looks like (1st photo)

At first, the problem was way more severe, so much that the ovalness of the circles was visible to the naked eye. Then I looked up how to fix it and every source said to tighten the belts. I tightened the belts and it didn't fully go away. Because of this, I tightened the belts too much and the y belt snapped. I had to buy new belts because of this and I figured it was just because the old belts were streched/worn out.
But the problem wouldn't go away with new belts. I tried tuning the tension using vibration frequency, I also checked the belt pulleys and it wouldn't go away.
Something I consider one of the largest clues is that the issue becomes severe and noticeable only at normal print speeds. There's only minimal (>1mm) deviation if I print super slowly.
If I turn on the steppers and try to move the x carriage or the bed back and forth, there is no slop in the system.
I've even tried to square the frame and gantry and tightened the eccentric nuts, there is no play anywhere.
Another thing I've noticed I consider a potentially useful clue is this (2nd photo)

There is always a small layer shift on the X axis when the slow first two layers are finished and the printer starts printing faster. I'm sure it's not elephant's foot because it's not squished outwards at all sides. Yes, the dimensions of the cube are spot on, but if I rotate the cube by 45 degrees, the dimensions are not correct anymore.
Is this possibly uneven belt tension? I've seen instances of this problem happening on CoreXY machines because of uneven belt tension.
There is literally NO MATERIAL on the internet about this issue happening from anything other than loose belts and it's driving me insane. I've been trying to eliminate this, but there has been no success whatsoever with anything I did.

P9650204.JPG P9650208.JPG P9650214.JPG P9650215.JPG
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Printer: modded Ender 3 V2 (movement system with belts, pulleys and steppers is stock)

tired trench
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check the grub screws on the gears themselves that are attached to the motors.

quick rapids
tired trench
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creality has a x and y tensioner that does the job pretty good.

tired trench
quick rapids
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I'm all out of ideas... guess the next logical step would be to start replacing the entire motion system until it gets fixed. What should I start with?

tired trench
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honestly how much is invested in that printer, mods upgrades etc.

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and technically you dont really have to replace the whole motion system just the the 2 motors. get some proper gears that you can tighten with a grub screw. and possibly new belts just in case. shouldnt be more than 50€

quick rapids
# tired trench honestly how much is invested in that printer, mods upgrades etc.

I've invested about as much in the printer as the purchase price is (around 250$) and countless hours of my time. It worked like a dream before, printed a benchy in 30 minutes. I have all the parts required to convert this thing to klipper at home already. I don't want to just throw it in the trash and buy a Bambu. But if my solving of this problem continues at this pace, I might as well have to. It's already taken me more than a week and I won't have much time in the coming days.

quick rapids
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It has to be something that can get worn or destroyed but also won't cause backlash or slop. I suspect the y belt tensioner as I said before, I also ordered a full V slot wheel replacement kit and a pre crimped y belt

quick rapids
# tired trench and technically you dont really have to replace the whole motion system just the...

Think I figured it out. It looks like it was a combination of multiple issues that have scaled with time and wear. Some of my oldest circular prints are perfect. On about 6 months old ones, I see a 0.3mm deviation that wasn't big enough to notice. Then my stock belt gave out and it became unbearable. The idler wheel on the Y axis was loose and wobbling side to side (bad design of the tensioner by Creality). I have crimped the new belts badly, so it was loosening during prints. Also, the stepper motor pulley is not round. It's a bit oval and I found that out because the bed did not move smoothly when I overtensioned the belts. I have fixed all the issues except the stepper pulley (ordered a new one) and the deviation is 0.3mm now when I print at stock speeds, about as bad as it was before. Hope replacing the Y stepper+pulley will fix the issue once and for all.

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Gonna cost me about 60€ if that's everything (hope it is)

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Going to close the thread when I get the parts and confirm the circles are perfect, is that okay?

tired trench
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sounds like you found the issue. 😄

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sounds good. give me a heads up and i will close the thread as soon as you say so.

tired trench
quick rapids
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I began to notice that the problem gets worse with speed so that 2x accel means about 2x the ovalness. I reverted all my upgrades and reassembled the printer with stock components (was a pain).

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It didn't fix it and I was out of ideas so I tried the last solution on my mind, changing fimware. I've previously avoided that because I thought that popular firmware doesn't just glitch out and cause the same artifact on every print. Turns out it does. Reverted back to non input shaping version of mriscoc firmware and the problem is gone.

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It's fricking insane to think firmware would cause such a problem.

tired trench
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that is really frustrating. but it can happen. but i feel like this is an edge case.

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at least you figured it out 😄