Polishing and Electropolishing for Machined Parts
Mechanical and electrolytic polishing with the Ra ladder stated in numbers: Ra 0.8 routine on sealing faces, 0.4 fine, 0.2 best, verified by profilometer per batch.
The Ra Ladder, Not Adjectives
Polishing is a numbers conversation. Our standard machining leaves Ra 1.6 to 3.2 on general faces. From there the ladder runs Ra 0.8 on sealing faces, Ra 0.4 with fine finishing passes, and Ra 0.2 at the top of what we hold routinely on polished features, verified with the profilometer rather than claimed. Roughness classes follow the ISO N-grade mapping our quality lab uses daily.
When to Choose It
| Goal | Method | Where it fits |
|---|---|---|
| Sealing faces, O-ring seats | Mechanical polish to Ra 0.8 to 0.4 | aluminum, stainless, brass |
| Internal passages and complex stainless geometry | Electropolish | even removal, clean passive surface |
| Optical-adjacent mounts and reflectors | Mechanical fine polish to Ra 0.2 | with CMM and profilometer verification |
| Cosmetic visible faces | Mechanical polish plus agreed face map | batch consistency sample |
| Deburr plus smooth in one step | Electropolish light | small stainless components |
Specifications We Control
| Item | Specification |
|---|---|
| Ra routinely held | Ra 0.8 standard on sealing faces, 0.4 fine, 0.2 best on polished features |
| Methods | Mechanical (wheel, paste, lapping), electropolishing for stainless |
| Verification | Profilometer reading per batch on specified faces; N-grade mapped report |
| Dimension rule | Polish stock reserved in route; final size CMM verified |
| Pairs with | Passivation after polishing on stainless; grinding before polish on flat datum faces |
How We Run It and Check It
Route logic: grinding sets flatness and parallelism on datum faces, polishing takes the surface down the Ra ladder on the faces that need it, and the profilometer confirms the callout per batch. Where the drawing gives a roughness grade (for example N4 or N5), we report in the same grade system so incoming inspection reads our numbers directly.
Material side: stainless steel, titanium, brass and copper. Related capability: surface grinding.
Cross entrances: by material | CNC machining | inspection and QC.
Frequently Asked Questions
Which Ra can you actually hold on a production batch?
Ra 0.8 micrometers is routine on sealing faces, Ra 0.4 with controlled finishing passes, and Ra 0.2 on polished features where the geometry allows it. Each batch is verified against the drawing callout, and the process note says which faces carry the Ra requirement.
Mechanical or electrolytic polishing?
Mechanical polishing suits flat and simply curved faces and tight edge control. Electropolishing suits stainless parts with complex internal geometry, because the acid removes material evenly everywhere the electrolyte reaches, and it leaves a clean passive surface that pairs naturally with passivation.
Does polishing change dimensions?
Yes, it removes material, typically microns. On tolerance-critical faces we reserve polish stock in the route and verify final size on the CMM. The drawing Ra requirement and the tolerance are reconciled at quote time.
Can you match polishing across batches for visible parts?
Yes, with an agreed face map and a retained sample. Cosmetic parts get a written agreement on which faces are visible and what the acceptance sample looks like, which is how batch-to-batch disputes are avoided.
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Quote with engineering feedback within 24 hours; prototypes in 7 to 15 days.
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