Surface Finish · Mechanical Finishes

Polishing

Progressive abrasives down to mirror: the finish for optics, molds and show surfaces.

Process specifications

Parameter	Value
Process group	Mechanical Finishes
Coating thickness	No coating — removes 5–20 µm through progressive abrasives, reaching Ra 0.05–0.4 µm mirror to near-mirror. On clear PMMA and PC it restores optical transparency to machined faces.
Tolerance impact	Subtractive: 5–20 µm comes off the polished faces, and hand-guided polishing slightly rounds sharp edges and can soften small details. Precision features need removal allowance or masking — flag mirror callouts at quote time so they enter the program.
Corrosion rating	Slightly improved — a smoother surface offers fewer crevice initiation sites, but no coating is added; corrosion behavior remains essentially that of the base material.
Appearance	Mirror to near-mirror brightness (Ra 0.05–0.4 µm depending on grade); on clear plastics, polished faces turn optically transparent instead of frosted-machined.

⚠ Not suitable for

Parts that must keep sharp functional edges — polishing rounds them (cutting edges, sealing lands, knife-edge seals); deep narrow slots and internal pockets the polishing media cannot reach; budget parts where bead blasting or as-machined already satisfies the spec (polishing is labor-intensive and priced accordingly).