CNC Milling ABS plastic (and outstanding issues)

Sacrificial wood clamps the piece so the cutter doesn't hit the steel vice. We have a new cutting lubricant in the bottom of the photo. A bottle of red helps the time pass.

Maria and I were working last week fabricating four identical complex pieces out of ABS plastic. Initially we though a lowish feed rate combined with a fast cutting speed would give the best results but actually that’s not true. ABS suffers from the material melting and reattaching tangental to the circular cutter, so the effect is that when you cut, you end up drawing frayed lines over the surface. This is particularly noticeable on 90 degree corners and in deep pockets (concave regions). The first fix we tried was running the same program a second time. This did improve the situation but not enough to give it a finished look.