CNC milling of plastic creates accurate parts from sheets, plates, and billets of engineering polymers. Compared with metal cutting, plastic milling calls for different tool shapes, speeds, and work-holding plans. This tutorial walks through every stage—from plastic selection to final deburr—so engineers and buyers can plan fast, repeatable runs.
Índice
Understand why you mill plastic on CNC
- Fast prototyping—no molds, no cure time.
- Tight tolerances for jigs, optical fixtures, medical housings.
- Stable dimensions compared with 3D-printed parts.
- Hybrid builds: mill inserts, then over-mold later.
Choose the right plastic to mill
| Plástico | Dureza (Rockwell) | Machining ease | Typical part use |
|---|
| POM (Delrin) | M80 | ★★★★★ | Gears, valves |
| ABS | R105 | ★★★★☆ | Enclosures, test rigs |
| PC | M70 | ★★★☆☆ | Clear guards, lenses |
| PEEK | M95 | ★★★☆☆ | High-temp insulators |
| UHMW-PE | D65 | ★☆☆☆☆ | Wear plates |
Tip: softer plastics smear if the tool rubs. Harder, glass-filled grades behave like soft aluminum—sharp carbide tools help.
| Tool material | Recommended plastics | Edge geometry | Coating benefit |
|---|
| Uncoated carbide | POM, ABS, Nylon | 0° rake, polished flute | Prevents chip welding |
| Diamond-like carbon | PEEK, carbon-filled PA | 5° rake | Lower friction, edge life ×3 |
| Aço de alta velocidade | UHMW-PE | Single-flute O-style | Cheap, easy to re-sharpen |
| PCD inserts | Fiber-filled PEEK | Negative rake | No fiber pullout |
Define feeds, speeds, and chip load
Use the chart as a starting point. Then tune by ear—chips should curl, not powder, and the surface should feel cool.
| Plástico | Cutter Ø | SFM | Chip load per tooth | Coolant |
|---|
| POM | 6 mm | 800 | 0.08 mm | Air only |
| ABS | 4 mm | 600 | 0.05 mm | Mist, low RPM |
| PEEK | 8 mm | 350 | 0.06 mm | Flood emulsion 5 % |
| Policarbonato | 3 mm | 500 | 0.04 mm | Air + drop oil |
Plan coolant and chip removal
- Compressed air clears long stringers from UHMW-PE.
- Water-soluble coolant stops heat cracks in PEEK and PC.
- Mist oil reduces gummy buildup on ABS and HDPE.
- Vacuum hood keeps fines off clear acrylic windows.
Fixture and clamp soft materials
Plastic warps under clamping stress. Use large pads or vacuum tables.
| Work-holding method | Best for size | Prós | Contras |
|---|
| Soft-jaw vise | <150 mm | Quick swap | Edge dents possible |
| Vacuum chuck | Up to 400 mm | No clamp marks | Poor for tiny parts |
| Double-sided tape | Thin sheet <3 mm | Cheap | Clean-up needed |
| Custom pallet | Repeat orders | Multi-part machining | Higher setup cost |
Roughing and finishing strategies
- Rough with a large two-flute end mill—leave 0.3 mm stock.
- Finish with a three-flute polished tool—0.05 mm step-over.
- For deep pockets, climb cut walls to avoid chip recut.
- Use trochoidal paths on PEEK to lower heat.
Prevent common defects in CNC plastic milling
| Defect | Reason | Fix |
|---|
| Melt edge | RPM too high, dull tool | Reduce SFM 20 %, change tool |
| Burrs on hole exit | Feed too low | Boost chip load 0.02 mm |
| Fuzzy surface | Incorrect rake | Use O-flute polished edge |
| Dimpling on thin sheet | Clamp force uneven | Switch to vacuum table |
Inspect and tolerance check plastic parts
- Measure warm parts? Wait 30 minutes for temperature equalization.
- Use rubber-tipped calipers to avoid surface dents.
- For optical parts, test haze with a 60° gloss meter.
Post-process and surface finish options
| Finish method | Result roughness Ra | Cycle time |
|---|
| Hand deburr | 1.6 µm | 30 s / edge |
| Vibratory tumble | 0.8 µm | 1-3 h |
| Flame polish (PC) | 0.3 µm | 15 s / edge |
| Vapor smoothing (PA12) | 0.4 µm | 10 min batch |
Production cost and lead-time table
| Lot size | Setup time | Machine time per part | Average unit cost |
|---|
| Prototype (1-5 pcs) | 2 h | 25 min | $85 |
| Short run (20-50 pcs) | 2 h | 15 min | $28 |
| Mid run (200 pcs) | 3 h | 12 min | $13 |
| High volume (>1k pcs) | 4 h pallet | 7 min | $7 |
Need outsourced CNC service?
Our team machines plastics, metals, and composite sheets on 3- to 5-axis mills, with post-polish, sheet-metal, and molding options. Send prints and get a same-day quote for turnkey production.
Summary: key steps for success
- Select a plastic grade that meets strength and machinability goals.
- Use sharp, polished cutters with chip loads high enough to shear, not rub.
- Control heat with air blasts or light mist—avoid flood on moisture-sensitive nylons.
- Fixture gently yet firmly to stop chatter without crushing.
- Finish edges by tumble or flame to reach the target gloss or seal.
Follow these guidelines and your next plastic CNC milling job will leave the spindle clean, the chips cool, and the parts exactly on size.
