Breaks in the cut of 4mm methacrylate, parameters in LightBurn?


I am engraving and cutting a 4 mm methacrylate (PMMA) with CO2 laser 60watts and in the cut I find that the edges are marked with scratches or small breaks in the material.

The cutting speed is 3 and the power 59%, I have tried with less speed and 60 or 65% power but the problem increases.

If I perform the same test on 3 mm methacrylate (PMMA) the marks on the edges of the cut hardly appear, although on some sides of the cut it still happens.

Is it a problem of speed/power settings in LightBurn, laser optics or methacrylate that is not pure PMMA?

I welcome opinions on this. :hugs:

You aren’t cleaning the pieces with anything afterward are you? Like alcohol?

Hi @Hank

I do not clean the material with alcohol, I just blow it with air and then wipe it with a cloth (similar to the one for glasses).


Well it’s stress crazing and it can happen on some acrylics more than others. It can be caused by the heating and cooling of the edges and also some chemicals, like alcohol can cause it.

I don’t know what the cure is besides try a different brand of acrylic.

You might try going a little faster and try to put less heat in the cut if you can but I dunno what else to suggest.

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Hi @Hank

Is it possible that “air assist” during cutting affects?

Thank you very much for your recommendations :hugs:

Yes, it is very possible. I was going to suggest that also, but I’m not sure if you want more or less or…?
usually for cutting acrylic I use as little air as possible, just enough to keep the lens clean.
I’m assuming that putting as little heat as possible into the cut and letting it cool as slowly as possible is the key, but that’s just my guess.
Experiment and see how it goes.


Hi @Hank

Following your indications, lowering the temperature (%), increasing the speed a little and deactivating the air in the cut, the result has been as expected.

Thank you for your support and your quick response. :heart_eyes: