Focus Height and Material Thickness of 3/8" Acrylic

I was reading previous post on cutting acrylic that is 3/8". I am attempting to do that same but I can not seem get it to work. I was wondering about the other settings like the focus height and the material thickness. For the material thickness, I have tried using the PG thick acrylic as well as uncertified with material thickness of 3/8". As for the focus height, I have tried the auto as well as manual set heights but none are able to cut through the acrylic. I was wondering if anyone here is able to help me or have had this issue before? Any help is much appreciated.

Speed and power are the two other variables that go along with focus. For manual focus on acrylic, it wouldn’t hurt to step the focus down under the surface about 1/3rd the material thickness, for this thicker material. But, you’ll still need to come up with settings that perform the cut for you. Power should be full. Speed is your primary variable.

3/8” > 6mm so don’t expect Proofgrade settings to work.

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Currently I have used 100/Full with different settings for 1,2 and 3 passes. But the more passes I do the acrylic is just melting. So I guess I just have to increase the speed?

So you would suggest i leave the material thickness as uncertified 3/8" and use a focus height of 2/8"?

You’re almost certainly going to need to make at least two passes at different focus heights. It just takes experimentation.

I will caution you to pay very close attention at all times, acrylic is (in my experience) the material most likely to catch fire.


I think in every picture ive seen of a glowforge destroyed there is a half burned sheet of acrylic sitting on the bed.


I usually leave focus height at 3/8" (or set focus feature) and drop the power a bit, increase speed, and run 3 passes. Clear acrylic sometimes takes 4! (I’ve learned to first check if the piece I’m cutting out can be move within the kerf to test it cut is complete before unpinning the sheet–that way I can always repeat the cut and know it’s in the same place, but once you shift the sheet, or the artwork, rarely can you get lined up perfectly again…).


This pic illustrates perfectly what is happening when the machine cuts, but also why you might have difficulty with thicker material. The beam has to be focused to vaporize the material, and can only be effective across a narrow range. Even if the first pass makes it halfway through the material, your second pass at a lower focus is going to have some of the beam power blocked/absorbed by the sides of the narrower channel above.

It can be done, but all that absorbed power creates heat, which will melt the material, further interfering with the ability to cut cleanly below - and also increasing the risk of fire.


Thank you so much everyone for all the input. Will definitely have to do some experimenting. Weirdest thing is that when I first received my glowforge, I cut the 3/8" acrylic cleanly in one pass but I don’t remember the settings. However, the crumb tray was not placed properly into the groves on the side. perhaps it is able to cut the 3/8" acrylic if I raised the acrylic sheet up a bit. Really need to try to figure out the focus height I used for that.

I was just cutting 3/8 plexi. Set depth at 9.1mm 100 speed 95 power.20200208_111939|243x500

Sounds like a cleaning may be needed.