What am I doing wrong acrylic coasters fail?

[illyse]

I made the thick acrylic Star of David coasters. I pulled the film off before cutting. I have some burn marks I’m cleaning off with Mr clean and some alcohol but it’s coming out strange not clear and there are ridges on done if the cuts. It’s strange. Ideas?

[hansepe]

That is called crazing and is generally caused by using alcohol on your acrylic. You get a lot of micro cracks and the alcohol just makes it worse.

Try cut another test piece. Use Dawn or another dish soap in a thin layer on top of your acrylic. Either lift the bottom off the tray or use something like a piece of draft board or scraps underneath as a sacrificial layer.

Rinse after cutting and you should like the results a lot more.

I don’t think I’d use Mr Clean either FWIW

Good luck.

[evansd2]

Yeah what he said about the crazing. But you also have acrylic vapor that condenses on the surface, leading to that hazy appearance. The soap trick will solve your problem with the hazing.

You may want to try elevating your acrylic to avoid flashback, as described here:

Suspended ablation

When cutting acrylic, I’ve observed what looks a bit like chipping along the cut edges. It’s one of those things that once you see it, you can’t stop seeing it - so consider that before continuing with this post Initially it seemed random, such that some edges were clean and others beset with ‘chips’: [Drawing3] Root cause is the build tray. When the laser cuts through the acrylic and hits the metal grid of the build tray, some of the photons are reflected back up to the acrylic, cre…

[Xabbess]

@illyse

I pulled the film off before cutting

Gotta ask…is it paper masking or plastic film? Plastic film usually equates to the acrylic being extruded rather than cast…which does not produce as nice of an engrave as cast. Plus…what everyone else said too, about your cleaning choices.

[illyse]

Thanks tons. Will put the acrylic under a piece of wood and try again. And ty for the alcohol info I had no idea

[illyse]

Plastic film. Ty

[illyse]

Ty ty ty

[rbtdanforth]

It is not all alcohol that is the problem, but mostly methanol (that may be included in ethanol.) I use hand sanitizer all the time, as it protects hands does not contain methanol.

Any new stuff can be tested on a bit of scrap and see the difference quickly,

[julschauer]

Yes. I lay a bed of chipboard down under all my cuts. It really helps protect the material during lasering.

[tjones]

@illyse

acrylic under a piece of wood

You want the wood under the acrylic, not the other way around.

[evansd2]

here’s another example of alcohol crazing.

Acrylic crazing fail

I’ve known for a while that acrylic plus alcohol is supposed to lead to cracks/hazing, commonly referred to as “crazing”. I’d never actually seen it until now. Here’s a cut piece of extruded acrylic. [image] Now I placed alcohol ink on it, thinking I might be able to get a stained glass effect. Like I said I had never seen crazing before, so I wondered if it were a myth. After about 20 seconds I noticed the cracks starting in from the edges. [image] The cracks were growing, slowly enough…

Seems to be more common with extruded acrylic.

@rbtdanforth cleans his acrylic with alcohol based hand cleaner I think, and never has crazing issues as far as I know. Whether that’s because of the type of alcohol or the type of acrylic isn’t exactly clear.

[jamesdhatch]

@evansd2

Whether that’s because of the type of alcohol or the type of acrylic isn’t exactly clear.

I believe it’s the purity of the solution. Hand sanitizer is 50-60% alcohol and IPA usually starts at 80%.

The acrylic probably also adds to the mess as you can see from the difference in susceptibility to hazing deposition.

[rbtdanforth]

@jamesdhatch

I believe it’s the purity of the solution.

“Alcohol” is the same name for many chemicals that C-O-H as the last carbon. With methanol that last carbon is the only carbon which makes it unique among alcohols, and it is methanol that attacks acrylic (and your hands). Therefore, because it is bad form (and illegal in some places) to have methanol in hand sanitizer, it is safe to use with acrylics. Denatured alcohol is (or used to be) part methanol to keep folks from drinking it without paying the alcohol taxes and thus hard on acrylics too.

[ricky2001]

In the photo it kind of looks like ice. I’m just curious if that’s how it looks in person? That could be a cool effect. Great work!