Lasering Acrylic - I Learned Something New

If this is common knowledge I apologize for being the last to know…

I’ve been messing around with acrylic, both cast and extruded. I have been etching pieces and then cutting them (also with the laser).

All looked great coming off the laser but there was some residue associated with the rastering. I cleaned them with that 91% isopropyl alcohol that’s sitting near Big Thunder. It did a great job of removing the residue but then this happened to the extruded acrylic only:

Tiny hairline cracks starting at the edges and propagating inward 1-3mm. These cracks were not there before cleaning with the alcohol.

So I did some reading and it turns out that hot spots, probably from reflections from the honeycomb bed, cause mechanical stresses in the acrylic that normally aren’t an issue. Solvents disrupt these stress points just enough to cause cracks to form.

The solution (no pun), is to use a non-solvent cleaner like this:

I’ve got some on order and will report results.

Again this seems to happen only to extruded acrylic. There is a difference in polymer length between the two products, but I’m not certain of the details. Cast is shorter I think.

ETA: This might be the reason gluing laser cut acrylic is dicey. Gluing cast acrylic might give better results!

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This is called crazing.
You can also use a recipe of:

1 part alcohol
1 part baby soap
20 parts water

also I believe there is some Novus on or above the laser worktable next to the overhead door.

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If you elevated the acrylic a little [putting it on a cardboard stand?] prevent the issue?

It would probably reduce the issue but the heat from any laser cutting or etching can induce those stresses.

There are actually two different kits of novus around the space. Like Jacob said, the laser committee novus stash should be on the table between the back door and loading dock door.

Cast acrylic sheets are ideal for laser cutting but they’re more expensive. Extruded works but it has a lot of shortcomings. Definitely worth the extra money to get cast acrylic. Main advantage of extruded is more precise and consistent dimensions.

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When I called Allied this week, they quoted me the same price for extruded and cast acrylic.

Was that because they now have a $30 minimum counter offer?

No it was for a full sheet of 3/16”. I wrote it down but don’t have it with me. Maybe $119 ?

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