01
Functional purpose
State corrosion, wear, conductivity, adhesion, cleanability, friction or other required performance separately from appearance.
Evidence route
Finish purpose and invoked specification/test
Surface requirement control
CNC surface finishes: separate texture, treatment, appearance and final dimensions.
As-machined roughness, blasting, anodising, conversion coating, passivation, plating, electropolishing and powder coating answer different needs. PartVerity closes function, visual criteria, masking, process sequence and post-finish inspection before release.
Decision premise
Finish question: what must the surface do, what may it look like, and which dimensions or interfaces remain critical after processing?
Engineering control
Six decisions before a finish is quoted as controlled
A finish name without class, colour, texture, masking, acceptance sample or test requirement leaves multiple legitimate interpretations.
02
Base material and condition
Confirm alloy, heat treatment and pre-finish surface because they influence process response and visual consistency.
Evidence route
Material/condition link and pre-finish requirement
03
Surface texture
Define machining marks, roughness, blasting medium or direction where function or appearance depends on texture.
Evidence route
Ra/Rz method where functional, or approved visual/texture standard
04
Coverage and masking
Identify threads, bores, contacts, sealing faces, datums and cosmetic zones that require coverage, exclusion or special handling.
Evidence route
Marked-up coverage and masking drawing
05
Dimensional interaction
Account for material removal or coating build and define which CTQs are controlled after the final process.
Evidence route
Pre/post-finish allowance and final-dimensional results
06
Visual and release criteria
Set lighting, viewing distance, defect limits, sample basis and authority for cosmetic acceptance where required.
Evidence route
Approved sample/standard, inspection record and release owner
Decision matrix
Finish families answer different requirements
The process family is only a starting point; applicable standard, class, provider capability and acceptance evidence must be specified.
| Finish family | Typical decision focus | Commonly missed control |
|---|---|---|
| As machined / specified roughness | Function, sealing, friction or cosmetic tool pattern | Measurement method and directional lay |
| Bead blasting | Uniform texture and pre-treatment preparation | Media, contamination, masking and edge effect |
| Anodising / conversion coating | Corrosion, wear, electrical or cosmetic requirement | Class/type, colour, dimensional effect and contact masking |
| Passivation / electropolishing | Surface chemistry, cleanliness or smoothing | Base-grade suitability and process verification scope |
| Plating / powder coating | Protection, appearance or wear layer | Thickness/build, threads, fit interfaces and adhesion criteria |
Claim boundaries
Finish statements that are too weak for release
‘Anodise black’ without type, class, colour basis or masking.
‘Smooth’ without a functional roughness method or visual standard.
Inspecting critical dimensions only before the coating process.
Treating one approved colour sample as proof for all alloys and surface histories.
Technical context
Use guidance to frame the review—not to replace project evidence.
External overview of common CNC post-processes and dimensional effects. The project specification and approved provider route remain controlling.
Protolabs Network surface-finish guide