Super fine hairline cracks around character edges when engraving clear acrylic

[John Kleiber]

A customer provided 3mm thick sheets to have engraved with clip art style images.

He identified the material as Polycarbonate. I happen to have some like thickness Polucarbonate here so I ran a test on it and it laser etches a really nasty looking yellow.

I then ran a test mark on a spare sample he provided and the results were like you would expect with acrylic, but...

But here is the problem, I looked closely at the engraving and could see super fine hair line cracks extending out from the character edges.

I tried various settings;

Power 35
Speed 300
Interval .065
In Focus and out of focus by 1/8"

Power 25
Speed 300
Interval .065
In Focus and out of focus by 1/8"

Power 20
Speed 300
Interval .065
In Focus and out of focus by 1/8"

Power 15
Speed 300
Interval .065
In Focus and out of focus by 1/8"


This setting worked the best. But when I turn the piece at just the right angle, I can see cracks.
Power 20
Speed 300
Interval .065
In Focus

I also noticed in general handling and DNA cleaning cracks developing on the outer edge of the material.

I have etched 1/4" Plexiglass which I presume was extruded, not cast, and never had this issue. At this point I am not sure what this material is and that is the problem or the issue is thickness.

Anyone have this type of issue?

acrylic_cracks_01.jpgacrylic_cracks_02.jpgacrylic_cracks_03.jpg

[Michael Henriksen]

That is because it is extruded acrylic and probably of poor quality. You shouldn't get that with cast acrylic. It engraves a nice white instead of grey as well.

[Mike Null]

It does appear to be extruded acrylic and such cracks are common; especially when dna is applied.

[Paul Phillips]

You didn't mention it but I would have to ask, did you try to clean it with Denatured Alcohol (DNA) or some type of solvent? I would agree, it appears to be extruded Acrylic not Polycarbonate, which as you saw does not cut or engrave well and leaves a putrid yellow smoke and haze on everything.

[John Kleiber]

I think I have found a reasonable solution. I will mask off the area and laser. Remove mask, perform a little minor weeding and its a done deal.

[Kev Williams]

Definitely not polycarb, as others have noted, yellow smoke is the giveaway. The inevitable yellow stain is almost- well, not almost, IS impossible to remove!

Another way to tell if it's polycarb, hit it with a fiber laser... with the right settings, it engraves almost jet black...
lexan.jpg

But stress cracks happen with cast too.
This is a piece of cast mirror. But, it was pretty old when I engraved it.
craze.jpg

-- and alcohol is the LAST thing you want anywhere near laser etched or cut acrylic!

[John Kleiber]

Masking worked to solve the issue. Cleanup was easy. Just dropped them in a flat tub with some mild dish washing soap and tape practically fell off.

acrylic_cracks_04.jpg

[Kev Williams]

That looks great John!

I love transfer tape for masking for the same reason, soak in some warm dishwater and it falls off!

--too bad you can't do that with wood...