Engineering Plastic Surface Finish Options: Polishing, Milling, & More

Surface Finish Options

1. CNC Milled (Standard) — Ra 0.8-3.2 μm

Default finish from CNC machining. Cost: included in machining price. Suitable for all engineering plastics.

2. Fine Milled — Ra 0.4-0.8 μm

Achieved with sharp carbide tools, high spindle speeds. Cost: +10-20%. POM achieves best milled finish; PPS GF40 is more difficult.

3. Polished — Ra 0.1-0.4 μm

Mechanical polishing with progressive abrasives. Cost: +30-60%. Best for medical devices and optical components. PEEK and POM polish well; glass-filled PPS is difficult.

4. Flame Polished — Ra 0.2-0.6 μm

Controlled flame melting. Cost: +15-30%. Best for POM. Not suitable for PEEK or PEI (thermal degradation risk).

5. Bead Blasted — Ra 1.0-3.0 μm

Fine beads create uniform matte texture. Cost: +10-15%. Best for aesthetic uniform finish.

6. Brushed — Ra 0.6-1.5 μm

Directional abrasive brushing. Cost: +15-25%. Specify brush direction in drawings.

How Surface Finish Affects Performance

· Friction & wear: Smoother surfaces reduce friction. Target Ra < 0.8 μm for bearings

· Cleanability: Smoother surfaces are easier to clean — critical for food/semiconductor

· Fatigue resistance: Polished surfaces improve fatigue life by 20-30%

Material-Specific Notes

· PEEK: Polishes to Ra 0.1-0.4 μm. Avoid flame polishing (degrades)

· POM: Easiest to polish. Flame polishing produces excellent results

· PPS GF40: Exposed glass fibers prevent smooth finish. Fine milling is best achievable

· PEI: Polishes to amber translucent finish