Hi, I got some dice blanks from amazon that specifically said “acrylic” in the description (though, I know that doesn’t necessarily mean they were, they did engrave nicely). I used 335/40/225lpi for a fairly deep engrave. It was probably a higher power than needed. I also masked them so I could easily use a dab of acrylic to help make the symbols being engraved stand out.
The problem I had was an alignment issue and getting the height right without the crumb tray. For a jig, in the end I made a thin box (about 2mm shorter than the dice) of card stock, taped it to a couple of scraps of draft board and taped it all to the bottom of the crumb-tray-free machine. Step one was cutting dice sized squares out of the top of the box. Then I could drop the dice into the holes, knowing that the icons I was engraving would be lined up, even if it didn’t look like it was on the software once it had refocussed on the dice.