Achieving Ra 0.2 Mirror Surface Finish in CNC Milled PEEK
Attaining an optical Ra 0.2 micron mirror surface finish on CNC machined PEEK demands single-crystal diamond (MCD) or polished PCD tooling, zero-vibration hydraulic chucking, and micro-depth spring passes.
Engineering Specifications & Parameters
Optimal Tooling Type
Monocrystalline Diamond (MCD) / Fine PCD
Finishing Spindle Speed
18,000 - 24,000 RPM
Finishing Stepover (ae)
0.02 - 0.05 mm (0.0008 - 0.0020 in)
Toolholder Runout (TIR)
< 0.002 mm (Hydraulic or Shrink-Fit)
Finishing Depth of Cut (ap)
0.02 - 0.05 mm
Achievable Surface Roughness
Ra 0.15 - 0.25 microns (Mirror Finish)
The Physics of Optical PEEK Surfacing
PEEK is a semi-crystalline thermoplastic with high elastic recovery. Achieving optical mirror finishes without post-polishing requires razor-sharp diamond shear edges rather than conventional carbide burnishing.
Precision Machining Protocol
Tooling: Monocrystalline Diamond (MCD) or ultra-polished fine-grain PCD ball end mills with cutting edge radius < 0.001 mm (1 micron).
Spindle Speed & Dynamic Balancing: 18,000 to 24,000 RPM balanced to G2.5 in thermal shrink-fit or hydraulic chucks (< 0.002 mm TIR runout).
Stepover Distance (ae): 0.02 to 0.04 mm stepover to maintain theoretical scallop heights below 0.1 micron.
Cooling: Clean filtered cold vortex air gun. Avoid mineral oil coolants for medical or semiconductor grade PEEK.
Critical Defect Prevention
Prevent heat accumulation during final passes; thermal expansion softens PEEK, turning crisp shear cutting into gummy smearing.
Frequently Asked Questions
Why is Monocrystalline Diamond (MCD) superior to carbide for mirror finishing PEEK?
MCD diamond tools can be sharpened to atomic-level cutting edges (<0.1 micron edge radius), slicing PEEK polymer chains without elastic tearing.
Why must petroleum-based coolants be avoided when machining medical PEEK?
Petroleum hydrocarbons can absorb into PEEK micro-voids, causing chemical contamination and failing biocompatibility certification.
