Help with Clean Cut of 1/2 Inch Acrylic

We had to cut several 1/2 inch clear cast acrylic sheets into multiple shapes. After several tries, we finally settled with these settings which is fairly decent and consistent: Full power at 105 speed (2 pass). However, the bottom surface of the acrylic has burn marks and some minor cuts around the edges of the shape. The top surface is pretty and clean.

Any tips to have both bottom and top surfaces have clean cuts? Like having a sacrificial material at the bottom or adding one more layer of masking sheet at the bottom will help? Looking for suggestions if anyone had similar issues and fixed them.

The machine is optimized for 1/8" material. Thinner is fine, up to 1/4 can be cut reliably if you persist. I’ve never been happy with the results but many here have.

1/2" is way beyond its design specifications. It will fit 1/2" on the tray for surface engraving, but cutting is going to be a challenge.

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what @eflyguy said. 1/2" acrylic is a big stretch for a 40w laser. it’s doable, but there will be sacrifices. you’re going to see a bigger slope on the sides, sometimes can get some slumping, and not always going to have the cleanest cuts.

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That is usually caused by flashback which is surprising since you are really stretching it at 1/2 inch, however, if it is caused by flashback you could reduce power just slightly or speed up the head a bit. Keep playing with those things until you get a clean cut with minimal flashback.

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@beerfaced Thank you for the reply. By flashback, I guess you are referring to the fire that is caused by the 2nd pass that is causing the marks and minor dents on the edges. The problem with having lower power on 1st or 2nd or both passes is the sides are not straight even if the material is cut all the way through. The shapes that we are cutting are supposed to freestand without support, so slanted sides are a problem.

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@shop Yes, the sloped sides and marks + dents on the bottom surface are there :frowning: To make it worse the 1/2 inch cast acrylic sheets have varying thicknesses by 0.5 to 1mm across the sheet (at random places including the centers). This makes it a nightmare to come up with a standard speed/power settings. Measuring the thickness all over the sheets is also not feasible.

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Just to be brutally blunt here, 1/2" material of any type it pretty much outside the scope of what the Glowforge can cut.

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So, what would be the minimum laser power recommended for 1/2 inch acrylic sheets? Something like a BossLaser with 100W power would suffice? The only laser cutter that we worked with is a GF Pro! Some suggestions would help. Hope moderators wouldn’t mind asking this here :slight_smile:

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No problem asking.

I believe a 60W CO2 laser would suffice for 1/2" acrylic.

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Any laser is going to leave a “slope” to the cut. The only way to get a 90° cut is with a saw.

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this is true because there’s an hourglass shape to a beam.

but the higher the power of the laser, the less dramatic it will be on thick acrylic like this. that’s because the slower speeds and multiple passes (especially if you don’t let it cool between) create some “slump” while you cut acrylic. higher power and faster speeds mean the heat is in the same spot for less time, creating less slump. when we cut 1/2" acrylic on a 75w universal, we get way less of that slope.

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we cut up to 1/2" on a universal 75w laser in my office doing model building.

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Can the laser you use make square enough cuts for that?

For a flat edge to stand on, a saw cut sanded to 320 or 400 and then flame polished with a torch would work.

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i haven’t tried, TBH. i’d have to test to see how steep it is. it’s fairly minimal. but how much there is depends on a number of factors, including which lens you have attached and what their focal points are.

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I have one of those electronic angle gauges used a lot in woodworking. It measured to 0.1º. At some point I tried to measure the slope/angle of the beam, I used the thickest material I could cut, and could not get a reading.

It’s obviously there if you use the kerf gauge that has you flip every 2nd piece, but I could not measure it. You could probably just calculate it from that tool. All mine ended up in the burn bin at some point.

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Since you’ve managed to achieve reliable cut results don’t let the naysayers on this thread pooh-pooh you out of what you’re doing. Congrats on getting 1/2" to work nicely.

For your flashback issues - yes you can put a sacrificial material underneath like a draftboard or 1/8" plywood. (I use copy paper under my acrylic instead of masking, that may not be enough given your power needs, might be more flammable). Also look up “pin beds for laser cutters” - the idea being to put a different set of tall supports under your cut than the honeycomb tray - as long as none of the supports are under the laser cut path you won’t get any flashback. Good luck!

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i’m not poo pooing doing 1/2". i’ve done it on the GF a few times and used the pieces. just noting the issues w/a 40w trying to cut that thick. if it works for your purposes with those limitations, it’s all good.

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I was trying to reference OP’s actual question which was about avoiding flashback. Was not referencing you :heart:.

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I cut 1/2 acrylic once. I will never do it again. The warping of the material pretty much ruined the part, it took five passes with 15 minutes between each pass to keep the material from melting back together. and it was overall not worth the effort.

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