Any circumstance where cast acrylic engraves clear?

[Ross Moshinsky]

Before I get myself into trouble I'm looking for some insight on something I may be unaware of.

I have a project I'm working on where I spec'd 1" clear cast acrylic. Got the product in and did a test engrave and it came out clear. Engraves exactly like extruded acrylic. Contacted the mfg and was told it's 100% cast acrylic, extruded 1" acrylic isn't even a possibility and told me the laser is out of focus.

I know they make extruded 24mm/1" clear acrylic. I have some in the shop right now. It was another circumstance where a vendor thought it was cast but it was actually extruded. So I know it's possible to get paper faced, 1" thick extruded acrylic. I was able to determine this 4 ways with this particular piece. I cut it on the CNC and it was a melty mess. I flame polished it and it got way better finish than cast normally does. It engraved clear. It crazed like crazy when I hit it with DNA, which doesn't happen with cast.

As for the laser being out of focus, I can check it tomorrow again, but based on the way it engraved, I pretty much know this isn't the issue.

So: Anyone ever hear of cast acrylic engraving exactly like extruded acrylic?

[Kev Williams]

Just did some tests--
Test engravings, 100 power 100 speed 300dpi both directions with my 40w LS900-

this is the engraved sides
ce1.jpg

this is the back sides
ce2.jpg

closeup of the engraved sides, in all cases the cast engraves to much whiter than the extruded--
ce3.jpg

Here I'm cutting an edge off--
ce4.jpg

This is very telling-- the cast is on top, and shows a definite blue hue where the cast has virtually no color-
ce5.jpg

to make sure it's not a lighting trick, I reversed them--
ce6.jpg

And this is the REALLY tell-- note the cast on top is shows lines, is shiny, and the chippy edge is the result of backflash on the table-
ce7.jpg
--but the extruded shows no backflash, it's more forgiving-- Why, because it melts and turns gooey--and stays gooey!
Note the edge looks mottled and matte finish- well, it wasn't like that to start with, it looked much like the cast...
it's like that now because of rolling my finger over the edge, the cut edge is soft enough that your fingers can 'move' the goo...
I rolled both edges, cast don't do that, the lasered edge is just as hard and goo-free as the top & bottom surfaces...
(I had pics of both edges shiny but the camera focused on my fingers instead of the plastic! )

Not sure if the blue color is an absolute tell, but the gooey cut edge is!

and I can tell you that yes, cast will craze, and badly!

[Kev Williams]

Just did some crazing testing- the extruded really took off, the cast not so much...
ce8.jpg

but the cast IS crazing, but ever so slightly...
ce9.jpg

This is a logo I cut out of some 20 year old cast mirror-
All this happened while trying to clean off the paper!
craze.jpg


to answer the original question, I see no reason for cast acrylic to behave like extruded...

[Mike Null]

Kev

I don't do a lot of cast acrylic other than signs but I haven't run into the crazing issue with cast. Extruded, now that's another matter.

[Neville Stewart]

If you can cut cast with a polished edge, it would seem like you could engrave it the same way but I'm guessing you weren't going for that look .

[Ross Moshinsky]

Just to be clear: No one here has experienced cast acrylic that engraves like extruded?

It's a big order for us and have to be careful with how I move forward so that I don't end up losing one of my best customers.

[Scott Shepherd]

I have not run into that Ross. We do a lot of cast acrylic, not normally engraved, but we have a lot of it in here and I use the drops all the time to check placement on critical things. I've never seen cast engrave clear. We also use a modified cast (Plexiglas MC) a great deal and that doesn't engrave clear either.

Not sure what you have going on, but I'd be interested to know what you figure out the issue is.

[Glen Monaghan]

You might try the burn test... Light a small piece (held with needle nose pliers, vice grips, etc.) on fire and observe. If the acrylic is extruded, it will burn quietly and drip flaming drops of molten acrylic. Cast will flame with crackling sounds and won't drip.

[Clark Pace]

Yes and i never did figure it out. On a laser i used to have. Ebay laser. Small one. The ones you see for around $400. When i engraved on cast is engraved clear. Then i could take it another laser and the same plastic would etch white. Very weird.

[Jerome Stanek]

Yes and i never did figure it out. On a laser i used to have. Ebay laser. Small one. The ones you see for around $400. When i engraved on cast is engraved clear. Then i could take it another laser and the same plastic would etch white. Very weird.

Did your laser have air assist. I can laser with the air off and I get clear but with the air on I get a white finish

[Clark Pace]

I dont remember it has been a few years. I think air assist. Dont have that laser any more.