If you haven’t found this topic, it’s all about my tests of Corian. Here is one of the posts that has both positive and negative engraves.
Doing the Delrin right now. I have some I got from Inventables. 1/4" pretty expensive as things go, about $27 for a 12x12 1/4 inch Black acetal. I did some small engraves to check it out and then tried cutting. One pass 100% power and 7 inches per minute. It cut through about .125" or halfway. Not sure how deep you need the relief. I’ll measure when I pull it out and post the pics.
Initial engraving tests had about .5 mm with 100% 335 speed and 340. More to come.
O crud. Forgot the last crucial step before making a stamp, reversing the design. Arg!!! Well now I definitely have to make a reverse engrave to be able to do a paper emboss from underneath.