Circles irregular

Machine: chinese laser with 400x600 co2 laser with nano m2 board

Board: replaced the board with cohesion’s board

Firmware: _Smoothie

Problem/ Question: I have trouble with circles. I asked help before, see this topic: Settings question
I have tried several things. Tightening the belts, lowering acceleration, lower G0 speed, pauze before start, and trying out all kinds of settings in Lightburn. The problem is that if the head rotates left, then a circle becomes a bit irregular in 1 direction. If the head rotates right, then the irregularities are mirrored in opposite direction. The irregularities look like overshoot. There’s a flat area where the X axis turns around. I hoped that tightening the belt would solve that, but it didn’t. The circles also seem a bit oval. But since the direction of the oval depends on the direction of the rotation, it doesn’t look to me like a wrong setting in the steps per mm resolution. And maybe oval is just an appearance from the flat sides and the direction flip, it seems not like a real oval.
We wonder if perhaps the amount of pulses per mm might be too low to get accuracy? Is that something we can change? Or is there any other setting that we have overlooked?

Btw, it would be cool if I could add a picture (I am not allowed). A pic might tell more than words.

That sounds like something loose in the stepper drive path. If you move to the middle of the table with system rriage i locked try to wggle the carriage. Any slack or allowed movement - find out where and snug it up.

I treid that before, but I will try again, thnx. I wonder if the cause could be the laser beam itself. Is is possible that the beam is not always exactly where it should be? It is angled 4 times by mirrors, could it be that an irregularity occurs there? Maybe there’s different quality mirrors?

If the laser dot is inconsistent in different areas of your laser bed, then the alignment is bad.

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