PMMA mills easily and that is exactly why people under-parameter it — then wonder why edges chip.
The parameter set
| Pass | Speed | Notes |
|---|---|---|
| Rough | 40–60% feed | Clear stock fast |
| Finish | 60–80% feed | Close surface |
| Spindle | 12,000–18,000 rpm | Cool throughout |
Defect prevention
- Always mist-cool — dry PMMA melts and welds to the bur.
- Use a fresh 2-flute bur; a dull bur tears the surface.
- Secure the disc; a vibrating blank chips the margin.
Start from a closed-grain PMMA disc for cleaner edges.
Parameters that work
| Pass | Feed | Speed |
|---|---|---|
| Rough | 40–60% feed | 14,000 rpm |
| Finish | 60–80% feed | 18,000 rpm |
Defect map
- Burr marks: worn bur — replace at 30 hours.
- Edge chipping: climb, not conventional, on the exit.
- Heat craze: cool with air; PMMA softens above 80 °C.