Surface Finishing for CNC Machined Parts
Professional surface finishing services for CNC machined parts.
Reviewed by PiPrecision Quality Team on March 12, 2026
Overview
PiPrecision coordinates machining, preparation, finishing, masking, and final inspection for anodizing, passivation, plating, powder coating, blasting, marking, and other drawing-defined treatments. The quotation identifies which operations are performed directly and which are assigned to an approved outside processor, together with the required certificate or test evidence.
Choose a Finish from Material, Function, and Drawing Requirements
PiPrecision coordinates finishing with internal machining and inspection. Availability, processing location, specification compliance, and testing are confirmed during RFQ review.
| Finish | Common materials | Drawing and inspection considerations |
|---|---|---|
| Type II / Type III anodizing | Aluminum alloys | Coating class, thickness, sealing, color, masking, rack marks, and dimensional growth |
| Passivation / electropolishing | Stainless steels | Alloy compatibility, governing standard, surface condition, cleanliness, and corrosion-test scope |
| Plating / conversion coating | Aluminum, steel, copper alloys | Undercoat, thickness, conductive areas, masking, adhesion, and post-plate dimensions |
| Powder coating | Sheet metal and machined metal parts | Color and gloss reference, texture, edge coverage, threads, grounding points, and assembly fits |
| Blasting / brushing / polishing | Aluminum, stainless steel, and other reviewed materials | Media or grit, direction, cosmetic zones, allowable witness marks, and starting surface |
Machined surface roughness and applied coating performance are different requirements. Define the pre-finish texture, final appearance, coating specification, and any test method separately.
What to Mark on the Drawing
Cosmetic and functional surfaces need explicit acceptance criteria so the finishing and inspection teams evaluate the same requirements.
- Finish specification, type or class, nominal thickness, color standard, gloss, texture, and approved sample when applicable.
- Threads, bores, bearing fits, sealing faces, grounding points, and other areas that require masking or controlled buildup.
- Primary cosmetic surfaces, viewing direction and distance, acceptable shade variation, and allowed rack or contact marks.
- Dimensions that apply before finishing, after finishing, or in both states.
- Required adhesion, coating-thickness, corrosion, conductivity, or color-measurement reports.
Documented Project Examples
Results below are specific to the linked project, part, volume, process, and inspection scope. They are not universal capability guarantees.
Engineering Resources
Use these guides to prepare drawings, tolerances, finish requirements, and inspection expectations before RFQ.
Capabilities
These are general, drawing-reviewed capabilities. The quotation confirms the applicable process, tolerance, inspection method, evidence, and any outside operation for the specific part.
Decorative sulfuric acid anodizing, various colors
Wear-resistant hard coat, up to 0.003" thickness
Durable organic coating, wide color range
Uniform matte finish for cosmetic applications
Stainless steel corrosion resistance treatment
Chemical conversion coating for aluminum
Stainless steel bright, smooth finish
Decorative black finish for steel
Nickel, gold, silver, tin, etc.
Permanent part marking and serialization
Quality Assurance
- Coating thickness measurement (eddy current, X-ray)
- Salt spray testing for corrosion resistance
- Adhesion testing (cross-hatch, tape test)
- Color matching with spectrophotometer
Specifications
| Type II Coating Thickness | 0.005mm - 0.025mm (0.0002" - 0.001") |
| Type III Coating Thickness | 0.025mm - 0.075mm (0.001" - 0.003") |
| Type II Standard Colors | Clear, Black, Blue, Red, Gold, Green, etc. |
| Type III Colors | Black only (dyeable to dark colors) |
| Type II Hardness | 300-400 HV |
| Type III Hardness | 400-500 HV |
| Type II Corrosion Resistance | 336+ hrs salt spray |
| Type III Corrosion Resistance | 1000+ hrs salt spray |
| Powder Coating Thickness | 0.05mm - 0.15mm (0.002" - 0.006") |
| Powder Coating Colors | RAL colors, custom matches |
| Powder Coating Salt Spray | 1000+ hrs |
Published capabilities are indicative and subject to drawing review.
Equipment
Primary Machines
- Anodizing Line — Type II & III sulfuric acid anodizing
- Powder Coating Booth — Electrostatic spray application
- Bead Blasting Cabinet — Glass, ceramic, aluminum oxide media
- Passivation Line — Nitric and citric acid processes
Inspection Equipment
- Eddy Current Thickness Gauge — Non-destructive coating measurement
- X-Ray Fluorescence — Precise thickness analysis
- Salt Spray Chamber — ASTM B117 corrosion testing
- Spectrophotometer — Color matching and verification
Materials
| Material | Grades | Applications |
|---|---|---|
| Aluminum 6061/7075 | All series | All anodizing types, chem film, powder coat, plating |
| Stainless Steel 300 Series | 304, 316, 303 | Passivation, electropolishing, bead blast, plating |
| Stainless Steel 400 Series | 410, 416, 440C | Passivation, black oxide, plating |
| Carbon Steel | 1018, 4140, C45 | Powder coat, black oxide, phosphate, plating |
| Titanium | Grade 2, Grade 5 | Decorative anodizing (colors only) |
| Brass/Bronze/Copper | C360, C464, C932, C110 | Clear coat, powder coat, patina |
Sample Parts
Why Choose PiPrecision
- 6+ yrs Export Experience
- 24h CAD Quote Review
- 1 piece Minimum Order
- 2 weeks Production Lead Time
Need Surface Finishing Service?
Initial review is targeted within 24 hours for a complete RFQ. Orders from one prototype are supported.
Request QuoteSurface Finishing Service FAQs
Process-specific answers from the PiPrecision Engineering and Quality teams.
How should I choose a surface finish for a machined part?
Start with function: substrate and condition, corrosion environment, wear, friction, electrical conductivity or insulation, chemical and temperature exposure, appearance, and regulatory needs. Then specify the process and governing standard, coating class or thickness, color standard, gloss or texture, sealing or post-treatment, masking, contact points, and inspection or test method. Finish names alone are not complete specifications; PiPrecision reviews compatibility, dimensional allowance, cosmetic limits, and supply-chain availability before commitment.
Answer owner: PiPrecision Engineering Team
Will anodizing, plating, or powder coating change dimensions?
Yes. Plating and powder coating generally add measurable material, while anodizing consumes some aluminum and builds some coating above the original surface; stripping, blasting, polishing, and etching may remove or alter the substrate. Nominal coating thickness does not always equal dimensional growth on a diameter or across two coated faces. Identify dimensions that apply before and after finish, coating thickness and tolerance, masking, thread-gauge state, and inspection stage so machining allowance and acceptance can be planned.
Answer owner: PiPrecision Engineering Team
Can finish color and texture be matched between production batches?
A process can be controlled to an agreed reference, but an exact visual match is not normally guaranteed without defined acceptance criteria. Alloy and temper, lot, machining marks, blast media, surface preparation, geometry, rack location, coating thickness, dye or powder lot, sealing, gloss, texture, and lighting can all change appearance. For cosmetic work, provide an approved physical limit sample or defined color and gloss standard, identify cosmetic surfaces, and agree viewing conditions, defect limits, lot-to-lot expectations, and any instrumental color tolerance before production.
Answer owner: PiPrecision Quality Team
Can selected areas be masked or laser marked after finishing?
Masking and post-finish marking can be reviewed, but feasibility depends on geometry, process temperature and chemistry, required edge quality, and contact or rack locations. Define masked threads, bores, grounding points, sealing faces, cosmetic zones, and allowed witness marks on the drawing. For laser marking, provide controlled artwork or text, location, orientation, size, contrast, serialization rules, machine-readable-code grade if applicable, and permanence or qualification requirements.
Answer owner: PiPrecision Engineering Team
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