Hi there,
I done quite a bit of engraving on various materials.
The main problem people have is that the spindle speed is too fast.
Whist engraving material such as mild steel, aluminium and brass the key is to have a medium to high spindle speed with plenty of coolant to flush out swarf.
On acrylics, acetals and PVC the melting point of this material is very low. Just imagine the heat generated from the tool friction itself. it gets hot quite quickly and then this heat is transfered to the plastic surface. This then only melts the material instead of cutting it.
On acrylics and acetal plastics I run a speed of approx 1500 rpm to 2000 rpm with coolant.
While on PVC plastic I reduce this speed to about 750 rpm also with coolant.
Feed rates vary on the complexity of engraving. I usaully run at about 60 to 100 mm/min.
Also tooling counts too. You could spend alot of money for bespoke engaving tools or use small ball nose cutters along with small spot drills.
I use dia 1mm to 2mm ball noses or use up to dia 3mm spot drills. It saves alot of money on tooling and results are very good to excellent.
Try it out, see what results you get. You will be pleased.
If you need any more info, be my guest and contact me.
Mel