Machining Guide
Technical plastics can be machined, milled, sawed, drilled, bent and polished. Each material and method has its own characteristics. Here we collect practical tips for successful machining.
General Tips
Sawing
Sawing is the most common machining method for plastics. Both band saw, circular saw and jigsaw work, but the choice of saw blade and settings is crucial.
Band saw
- Best choice for thick plates and round bars
- Use blades with 3-4 teeth per inch (TPI) for thick material, 6-10 TPI for thinner
- Band speed: 300-600 m/min depending on material
- Low feed to avoid the blade getting stuck
Circular saw
- Good for straight cuts in plates
- Use blades with carbide tips and positive tooth angle
- Many teeth (60-80) give finer cuts
- Cutting speed: 1,500-3,000 m/min
- Support the material near the cut to avoid vibrations
Milling
Milling gives high precision and good surface finish in plastics. Conventional milling machines work, but there are special milling cutters for plastics that give better results.
Recommended parameters
| Parameter | Soft plastic (PE, PP) | Hard plastic (POM, PA) | High-performance (PEEK) |
|---|---|---|---|
| Cutting speed | 200-500 m/min | 200-800 m/min | 100-300 m/min |
| Feed per tooth | 0.1-0.3 mm | 0.1-0.5 mm | 0.05-0.2 mm |
| Cutting depth | 1-5 mm | 1-8 mm | 0.5-3 mm |
Practical tips
- Use milling cutters with 1-2 flutes (not 4+) for better chip removal
- Positive spiral angle (upward cutting) gives better chip evacuation
- Carbide or diamond tools give longer tool life
- Avoid stopping the mill in the material, it can cause melting
- Cool with compressed air, not cooling liquid (exception: PEEK)
Turning
Turning of plastics gives excellent surface finish and tight tolerances, especially in materials like POM, PET and PEEK. Plastics require different settings than metal.
Recommended parameters
- Cutting speed: 200-500 m/min (soft plastics), 100-300 m/min (hard/filled)
- Feed: 0.05-0.3 mm/rev
- Cutting depth: 0.5-3 mm (finishing), 1-5 mm (roughing)
- Tool: HSS or carbide with positive chip angle (6-15 degrees)
Common problems and solutions
- Long chips: Increase feed or use chip breaker
- Poor surface finish: Reduce feed, increase cutting speed, check that the tool is sharp
- Dimensional deviation: Plastic expands when heated. Let the part cool before measuring
- Ovality: Use soft jaws or support sleeve for thin-walled parts
Drilling
Drilling in plastics requires adapted drills and lower speeds than in metal. Standard metal drills work but often give poor surface finish and can cause cracking.
Drill geometry
- Point angle: 60-90 degrees (not standard 118 degrees as for metal)
- Spiral angle: 12-16 degrees (slower spiral for better chip removal)
- Cutting edge angle: 0-4 degrees positive
- Special drills for plastics are available and recommended for precision
Practical tips
- Drill with low speed and even feed
- Pull out the drill regularly to clear chips (peck drilling)
- Support the material underneath to avoid breakout at breakthrough
- For deep holes: cool with compressed air and use a step drill
- PA (nylon) can give fuzzy holes. Use an extra sharp drill
Bending
Many thermoplastics can be bent with heat. The material is heated locally to the softening temperature, bent to the desired angle and held in place until it cools.
Bending temperatures
| Material | Temperature | Comment |
|---|---|---|
| PMMA | 150-170 °C | Bends easily, good formability |
| PC | 150-165 °C | Requires even heating |
| PVC | 100-140 °C | Low bending temperature |
| PP | 150-170 °C | Springs back slightly |
| PE | 120-140 °C | Soft, bends easily |
| POM | Not suitable | Cracks when bending |
Methods
- Heat line: Heats a narrow line for sharp bends. Best for thin plates (1-6 mm)
- Oven: Heats the entire plate evenly. Best for large bends and thicker material
- Hot air gun: Local heating. Good for repairs and small jobs
Welding
Thermoplastics can be welded by melting the edges together. Welding gives stronger joints than bonding and is the standard method for tanks, pipes and containers.
Hot air welding
Most common method. A hot air gun melts the edges and a weld rod fills the joint. Works for PE, PP, PVC and PVDF.
Temperature: 250-350 °C depending on material
Extrusion welding
An extruder melts the weld rods and applies them to the joint. Faster than hot air welding for thick materials. Common for tanks and large structures.
IR welding
Infrared radiation heats the edges without contact. Gives very clean welds. Used for PVDF and other materials that require high purity.
Polishing
Transparent plastics like PMMA and PC can be polished to optical clarity. Polishing removes scratches and gives a glossy, transparent surface.
Methods
- Machine polishing: Polishing wheel with polishing compound. Start with coarse and work towards finer grit
- Flame polishing: A propane flame melts the surface to a glossy finish. Fast but requires practice. Works best for PMMA
- Diamond polishing: Diamond paste on a felt wheel. Gives the best optical quality
Tips
- Sand first with 400, 800, 1200 and 2000 grit before polishing
- Keep low pressure and even speed to avoid overheating
- PMMA polishes easily. PC requires more work due to higher hardness
- Anti-static treatment after polishing reduces dust accumulation
Bonding
Bonding is an alternative to welding, especially for materials that cannot be welded or when different materials need to be joined. The right adhesive choice is crucial.
Adhesive types
| Adhesive type | Suitable materials |
|---|---|
| Methyl methacrylate (MMA) | PMMA, ABS, PC, PS |
| Epoxy | Most plastics (with surface treatment) |
| Cyanoacrylate (super glue) | ABS, PC, POM, PA |
| Solvent-based | PMMA, PS, PVC, ABS |
| Polyurethane | PE, PP (with primer) |
Difficult-to-bond materials
PE, PP and PTFE have low surface energy and are difficult to bond. Surface treatment is required:
- Flame treatment: Brief exposure to an open flame oxidizes the surface
- Corona treatment: Electrical discharge activates the surface
- Primer: Special primer increases adhesion
- Sanding: Coarse sanding increases contact area
CNC Machining
CNC machining of plastics gives high precision and repeatability. Most technical plastics are well suited for CNC milling and CNC turning.
Best materials for CNC
- Best machinability. Excellent surface finish, tight tolerances
- Very good dimensional stability, fine surface
- Good machinability, high strength
- Requires carbide tools but gives excellent results
- Good machinability, dimensionally stable
POM:
PET:
PA6.6:
PEEK:
PEI :
Tolerances
Achievable tolerances depend on material and geometry:
| POM, PET, PEEK | +/- 0.02 mm |
| PA6, PA6.6 | +/- 0.05 mm |
| PE, PP | +/- 0.1 mm |
| PTFE | +/- 0.1 mm |
Tolerances apply at room temperature after acclimatization. Moisture-absorbing materials (PA) can change dimensions.
Material-specific tips
POM (Delrin)
Excellent to machine. Gives fine surfaces and tight tolerances. Be careful with overheating. POM releases formaldehyde when burned, ensure good ventilation. Low friction makes chips slide off easily.
PA (Nylon)
Absorbs moisture (up to 3%). Let the material acclimate before machining. Can give fuzzy surfaces when drilling. Use sharp drill with adapted geometry. Machine dry material for best results.
PE-UHMW
Soft material that requires support during machining. Tends to "pull away" from the tool. Use high feed and low speed. Sharp tools are especially important. Difficult to maintain tight tolerances.
PEEK
Expensive material, plan machining carefully. Requires sharp carbide tools. Withstands high temperatures but generates much heat during machining. Cool with compressed air. Can be machined to very tight tolerances (+/- 0.02 mm).
PMMA
Brittle material. Use special tools for plastics. Saw with fine-toothed blades. Drill with plastic drill (60-90 degree point angle). Can be flame polished to optical clarity. Protect the surface with protective film during machining.
PTFE
Soft and elastic. Requires support during machining. Tends to deform under pressure. Use sharp tools with large chip angle. Difficult to maintain tight tolerances due to material elasticity. Machine with oversized dimensions and let the part rest.
Need help with machining?
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