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Machining Cast Acrylic: Single-Flute "O" Flutes, Feed Rates, and Preventing Chip Melting
Category: Shop Floor & Materials • Published: 2026-08-17 • By Muhammad Ali
Machining cast acrylic (PMMA) requires a completely different operational mindset than cutting wood. Wood is a composite porous fiber; acrylic is an amorphous thermoplastic with a low glass transition temperature ($T_g \approx 105^\circ\text{C}$).
If you use a multi-flute router bit on acrylic, friction instantly melts the plastic, welding chips to the bit in a catastrophic melted ball.
### The Single-Flute 'O' Flute Solution
Cast acrylic must be cut with a **Single-Flute Solid Carbide 'O' Flute** bit:
- Features an ultra-wide, mirror-polished chip trough that evacuates the hot plastic chip in a single upward curl before it can re-weld to the edge.
- Razor-sharp cutting edge with high positive rake ($18^\circ$) to slice cleanly without chipping brittle edges.
### Production Baseline for 10mm Clear Acrylic
- **Spindle Speed:** 16,000 RPM
- **Feed Rate:** 2,400 mm/min
- **Chip Load:** $0.15\text{ mm}$ per tooth
- **Tooling:** 4mm single-flute upward spiral 'O' flute
- **Depth per Pass:** Full depth with a $0.3\text{ mm}$ radial finishing pass.
This combination produces a crystal-clear, semi-gloss edge directly off the machine with zero micro-fracturing and zero need for tedious manual torch flame polishing.