Hmm well had a go today on some perspex and got pretty horrible results. It melted so bad that I had to peel the plastic off the cutter with pliers!

I had it around 1-1.5m with 10k rpm with 4mm DOC. I did try upto 2.5m but it started chipping the surface although it wasn't melting much at all.

How can you tell if its cast? The stuff had a white backing on one side and clear on the other.