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View Full Version : Acrylic troubles (engraving residue and stress cracks on vector)



donald bugansky
02-20-2010, 11:40 PM
How about leaving the power down but run the engraving twice? Also, taking it a little out of focus on the second pass may help with that "frosty white" look.

I took a 3 by 12 piece of acrylic and engraved the same text on the left side of the sheet with different settings and then marked the settings I used on the acrylic sheet with a sharpie for future reference. This way I can see the result I want and then just use the settings I marked with the sharpie.

As far as the stress cracks...a number of posts around Christmas (http://www.sawmillcreek.org/showthread.php?t=127667) relative to this issue (don't use brake fluid - don't ask). Net..only certain cleaners can be used or you will get stress cracks and some can take a few weeks to show up.

Look for threads from Rodne Gold (http://www.sawmillcreek.org/showthread.php?t=22369). He has a great write-up covering the topic.

Zsolt Paul
02-21-2010, 12:04 AM
As you can see from the subject title, I had managed to get all acrylic related troubles into one job! Way to go! I never did pay much attention what kind of acrylic I was using, simply because I didn't need to. Everything I had always done with acrylic always came out perfect....until today that is. After reading some posts, I think it may be b/c my previous supply has always been cast acryilic and perhaps today I got my first batch of extruded acrylic and thus became well aquainted with stress cracks. Besides the stress cracks, I also got a residue around the edges of the engraving (all text, so around the letters) which proves to be very difficult to get off. Here is what I did:

1: vector cut shape - no problems, came out great
2: engraved text with 35% power with my 100W laser (set 100% brightness on laser)
3: Engraved nice and white, but residue around each letter...so I cleaned it with DNA.

I KNOW there were no stress cracks prior to engraving (I checked). I only used DNA on the engraving, not on the vector cuts, however when I sprayed it out of a spray bottle it might have gotten on edges (which would explain why the cracks are only in certain places)

I suspect that the residue around the text is due to too much power. However, when I used my "old" settings it didn't engrave white enough. When I turned the power up it engraved nice and frosty white. Is this another sign that I might have been using extruded instead of cast?
Q1: Is it possible to get a nice white engraving out of an extruded without getting the nasty residue? It seems that turning the power down would get rid of residue, but will also not be as white.... catch 22?
Q2: If I do need to keep power up to get the nice white color, what can I use to clean up the stubborn residue around the letters? (Since I can't use DNA it seems...)

Thanks!

Zsolt Paul
02-21-2010, 12:05 AM
Yeah, I read through those posts. Didn't walk away with a clear understanding whether DNA is acceptable or not to use on acrylic?

Is there a way of saving this work? Is there a way to totally clean off the residue around text? Is there a way to get rid of stress cracks? I read about "fire". Is that just a blow torch going back and forth quicly across the cracks?

Joe Pelonio
02-21-2010, 12:27 AM
Any high heat will modify the molecular structure of acrylic and leave it subject to cracking when exposed to solvents. Flame polishing and even the heat from a router can be enough.

Denatured alcohol contains gasoline, which is a solvent so do not use it on laser cut acrylic. If you need to clean off stickiness or residue use a non-ammonia window cleaner. I like Sprayway from Costco.

Once you have those cracks you cannot get rid of them.

Dan Hintz
02-21-2010, 8:28 AM
For a nice white engraving, cast was the way to go. You won't get nearly the same engraving contrast with extruded.

Zsolt Paul
02-21-2010, 9:52 AM
What about recutting the edges by a 1/32" or 1/16" to cut off the cracked edges? Wonder if the cracks that have already developed continue?

For cleaning, would the orange hand cleaner with pumice work or is that solvent based? I am thinking the pumice would help remove the residue...

Mike Null
02-21-2010, 11:30 AM
The cracks are likely to continue if it's extruded. Cleaning with a plastic polish will work or you can use transfer paper and engrave through it. I think pumice will leave fine scratches.

I use dna as my standard cleaner for all cast acrylic.

Zsolt Paul
02-21-2010, 9:08 PM
So DNA is OK on cast acrylic, just not on extruded?

art baylor
02-21-2010, 9:40 PM
We used to use a pair of polorized filters to see stress crazing. Works very well.
And, there ain't no gasoline in DNA.

Art

Joe Pelonio
02-21-2010, 9:43 PM
So DNA is OK on cast acrylic, just not on extruded?
No, it will do the same to the CUT edges of both. Do an experiment and cut a small square then wipe it with DNA, you can watch the cracks appear right before your eyes.

I have never seen it cause cracks on the surface of engraved acrylic, only on the cut edges but then I don't engrave extruded, because it looks muddled.

Mike Null
02-22-2010, 5:38 AM
Joe

I have never experienced any cracking or crazing using dna on cast acrylic.

Frank Corker
02-22-2010, 8:54 AM
Mike I haven't either, bar one occasion, but it was alcohol on a piece which had been heated up very hot. The crazing is pretty because it's actually inside and not on the outside top or bottom. That said it was the only time, normally I get no fracture marks and I almost always use isopropanol alcohol.

Joe Pelonio
02-22-2010, 9:35 AM
Joe

I have never experienced any cracking or crazing using dna on cast acrylic.
Odd, I wonder if it's a brand issue.

Mike Null
02-22-2010, 10:09 AM
Joe

I mostly use 1/8" from Johnson Plastic which I reverse engrave and clean with dna.

John Noell
02-22-2010, 12:53 PM
And, there ain't no gasoline in DNA. Art
Nope but ethanol sure is a "solvent" (as is the methanol most often used to denature it).

Joe Pelonio
02-22-2010, 2:24 PM
Joe

I mostly use 1/8" from Johnson Plastic which I reverse engrave and clean with dna.
To tell you the truth I never tried DNA on th edges of 1/8, just 1/4".