Machining plastics
Turn acetal at 300 – 500 m/min, where Ensinger’s and MCAM’s ranges overlap, with a sharp tool, a nose radius of at least 0.5 mm, and no coolant. Pick a plastic and the operation for the cutting speed, feed and tool angles its makers publish, the spindle speed at your diameter, coolant, annealing and how much it grows with heat.
Where the makers’ ranges do not overlap the tool says so: Ensinger turns PTFE at 150 – 500 m/min, Chemours at 60 – 150 m/min for a fine finish. The edge is drawn in section with its clearance and rake.
Where Ensinger and Mitsubishi Chemical (MCAM) overlap. The supplier's guidance for your grade governs.
- Cutting speed vc
- 300 – 500m/min
- Spindle speed at Ø 50 mm
- Feed f
- 0.1 – 0.4mm/rev
- Clearance α
- 6 – 8°
- Rake γ
- 0 – 5°
- Nose radius r
- ≥ 0.5mm
- Coolant
- Dry or air; coolant for deep holes
- Anneal (stress relief)
- 155 – 162°C
- Expansion
- 110 – 140µm/(m·K)
- Ø 50 mm grows per 10 °C
- 0.055 – 0.070mm
- Easier to machine than the most machinable brass: grind the tools as for free-cutting brass, with back rake and a large chip breaker. (DuPont)
- Post-shrinks by up to about 2.5 %, so local overheating warps it: keep the heat input low. (Ensinger)
- It springs back: ream off at least 0.15 mm, and take thread finishing cuts of at least 0.15 mm. (DuPont)
- The chips burn: clear them away rather than let them pile up. (DuPont)
How it’s calculated
Spindle speed n in r/min from the cutting speed vc in m/min at the diameter D in mm: the work for turning, the cutter or drill otherwise. DuPont turned Zytel 101 of Ø 60 mm at 185 m/min and 980 r/min. A size grows by D · α · ΔT.
| Maker | vc, m/min | f, mm/rev | α, ° | γ, ° |
|---|---|---|---|---|
| Where they agree | 300 – 500 | 0.1 – 0.4 | 6 – 8 | 0 – 5 |
| EnsingerTECAFORM AD, AH | 300 – 600 | 0.1 – 0.4 | 6 – 8 | 0 – 5 |
| Mitsubishi Chemical (MCAM)Ertacetal POM, Ertacetal C | 200 – 500 | 0.05 – 0.5 | 5 – 15 | 0 – 10 |
| Material | Turning vc, m/min | Anneal, °C | Expansion, µm/(m·K) |
|---|---|---|---|
| Acetal (POM) | 300 – 500 | 155 – 162 | 110 – 140 |
| Nylon (PA) | 250 – 500 | 150 – 180 | 95 – 130 |
| PEEK | 250 – 300 | 200 – 250 | 45 – 50 |
| UHMW-PE | 250 – 396 | 130 | 200 |
| PTFE | 60 – 500, differ | ≤ 327 | 124 – 130 |
| G10 (epoxy-glass) | — | — | 10 – 20 |
| Maker | Grade | Anneal, °C | Hold |
|---|---|---|---|
| Ensinger | TECAFORM AH (POM-C) | 155 | 1 h per 10 mm of wall; heat over 6 h, cool 20 °C/h |
| Ensinger | TECAFORM AD (POM-H) | 160 | 1 h per 10 mm of wall; heat over 6 h, cool 20 °C/h |
| Mitsubishi Chemical (MCAM) | POM-C, POM-H | 155 | 10 min per mm; heat 10 – 20 °C/h, cool 5 – 10 °C/h |
| DuPont | Delrin (POM-H) | 158 – 162 | 30 min to heat through, then 5 min per mm, in air |
| Maker | Grade | Expansion, µm/(m·K) | Over |
|---|---|---|---|
| Ensinger | TECAFORM AH (POM-C) | 140 | 23 – 100 °C |
| Ensinger | TECAFORM AD (POM-H) | 130 | 23 – 100 °C |
| Mitsubishi Chemical (MCAM) | Ertacetal C (POM-C) | 125 | 23 – 100 °C |
| Mitsubishi Chemical (MCAM) | Ertacetal H (POM-H) | 110 | 23 – 100 °C |
| DuPont | Delrin | 120 | 23 – 55 °C |
Why do plastics machine differently from metal?
Plastics conduct heat poorly and expand far more than metal (Chemours puts PTFE at nearly ten times), so the heat stays at the cut: a dull edge rubs, smears and leaves the part oversize until it cools. The makers ask for sharp tools with generous clearance, cuts of at least 0.5 mm so the edge cuts rather than rubs, chips cleared away to carry the heat, and parts measured at room temperature. Holes deeper than twice the diameter are where coolant earns its place.