Cut alignment not repeatable?

I have a Kentoktool LE400Pro, and so far it seems to work fine with LightBurn.

The first few test cuts, I would re-run the exact same pass, without moving the piece, to make a deeper cut, and it worked fine.

Now, today, I tried doing that again, and found the second pass was off by a few millimeters, ruining the entire thing.

I didn’t use the “pass” parameter. If I use that, the repeat passes are in perfect alignment. But if I simply press “Start” right after it finishes a cut to re-run the exact same cut, then it seems to slightly lose alignment.

How do I prevent LightBurn from using a different alignment on each run? I need to be able to place the workpiece in an exact location and have the cut be repeatable.

If its for CUTS I would set the passes to whatever is your max needed, then just stop job once it has cut all the way through.

My point is, the position LightBurn uses as the origin seems to randomly shift a little each time.

So if I want to cut a pattern exactly in the middle of a piece of wood, LightBurn will cut is 2mm offset along the y-axis, or 3mm offset along the x-axis. Each run seems to be randomly shifted.

I’m trying to figure out what causes it. I’m pretty sure I’m not accidentally nudge my workpiece, and I’ve ensured all my locknuts are tight, so nothings slipped. My machine is bolted in placed to the table, so it can’t move relative to the cutting surface.

I’ve also tried starting the cut from different places, first going Home, but also from first doing a Frame, since each leaves the head at a different starting point. But so far I can’t reliably reproduce the problem.

If it is randomly shifting that indicates it is more than likely a mechanical issue and you are missing checking somewhere with the belts, wheels or grub screws.

Lightburn uses the same coordinates to produce the same G-Code, so if the position of the laser head isn’t correct, then the machine is not working properly.

Make sure it’s mechanically secure by checking everything. This list is for Sculpfun lasers, but you’ll recognize all the parts:

If the machine has homing switches, then usual problems seem to be interference with the home position or stability after homing: cables getting in the way, loose brackets, even a loose laser head.

If it doesn’t have homing switches, then you must ensure it starts out at exactly the same position every time. This usually involves putting it firmly in a corner before turning it on.

When the machine is set up properly and everything is secure, then the laser will hit the same spot every time.

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