Line work messed up. Shifted in Y direction after the move

[soswow (Aleksandr Motsjonov)]

I have what seems to be 40W co2 laser (big chinese blue). I’ve completely taken it apart, gave all hardware a full clean up and paint. New mirrors, new lens. Mirrors aligned.
The problem I am having looks like this:

(Green pen shows movement).

Design has two of those shapes so I can demonstrate the problem.

In these final tests I had two layers each with one sublayer (second sublayer does quicker, lighter pass) I did that to show, that when it goes second time (not right after the move) it does move where it suppose to.

Here is an animation to give full picture of movement: https://imgur.com/a/UGk9hgv

What’s interesting - the effect is not as pronounced when I do it in farthest (right) X position. Closer to the end of the axis):

Here are my machine settings:

I believe I’ve lessened Engraving X acceleration (mm/s²) a bit since taking a picture. As well as Max acceleration (mm/s²) on X to 10K.

So, what I can determine is that when it moves in Y direction, it doesn’t do a full

My question to your folks is what can it be? What should I tweak? Debug?
Acceleration? Physical stuff? Any idea where to look?

[ednisley]

@soswow

what can it be

Mechanical backlash, pure and simple.

The problem is mostly in the Y axis:

The wobbles in the arc suggest the Y axis belt(s) aren’t tight enough.

There may be a loose screw in a motor pulley, although the pulleys are often press-fit to the motor shafts. If there’s a jack shaft across the back of the machine, make sure the screws in the shaft couplers are all tight against the shaft flats.

The gantry must be square with respect to the Y axis linear bearings. If the machine has two Y-axis belts, they must be properly aligned on the drive pulleys and not off by one tooth (or more!).

The entire laser head can be loose on the X axis belt follower, so check those screws, too.

Aaaand it’s possible the screws have stripped threads or the holes are overly large.

If the lock ring holding the focus lens in place isn’t snug, the lens can rattle around inside the head.

Plenty of places to check!

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[soswow (Aleksandr Motsjonov)]

oh yeah! thank you very much. I’ve learned a bunch.
1st - I’ve fixed it. I was surprised to find one of the couplers at the back (from Y axis motor to shafts) was loos. I guess it was carrying a load only on right side and moving left side via X gantry.
2nd - I’ve found this video https://www.youtube.com/watch?v=T8MCU5sn2ow which helped me understand the nature of resulting line.
3rd - Finally I’ve tightened all belts a bit more. Had to replace bolts that pushing idler away for tension for longer ones.
4rd - There is still a bit of slack in the head, which I can see caused by bearing block not being 100% tight. but I might live with that for now, though changing it won’t be a problem.

[ednisley]

@soswow

• one of the couplers at the back
• replace bolts that pushing idler away for tension

Excellent!

Needing longer bolts suggest the belts may be stretched or, more likely, the surface has worn. The sides of the teeth may also be worn enough to allow slight slippage, so give the belts a careful look.

But it definitely works better now!