CNC Machining Surface Finishing Options
A practical guide to finishing CNC machined parts – anodizing, powder coating, electroplating, passivation, polishing and more. Understand what each finish does, when to use it, and how it affects thickness, roughness and cost.
Free Consultation+3-5 Days
Finishing Lead Time
Ra ≤0.1μm
Mirror Polish
China
Factory
12+ Options
Finishes
Materials
| Grade | Properties | Typical Applications |
|---|---|---|
| Aluminum (6061, 7075, 5052) | Anodizing (II/III), powder coat, bead blast, polish, brushing, painting – best all-round finishing candidate | Enclosures, brackets, heat sinks, decorative and structural parts |
| Stainless Steel (303, 304, 316L, 17-4PH) | Passivation, electropolishing, bead blast, polishing, black oxide – corrosion-focused finishes | Medical, food, marine and chemical parts |
| Carbon / Alloy Steel (4140, P20, H13) | Zinc/nickel/chrome plating, black oxide, powder coat, painting – wear and appearance | Tooling, shafts, gears, industrial hardware |
| Titanium (Gr2, Gr5) | Passivation, bead blast, polish, anodizing (decorative), DLC/hard coatings | Aerospace, medical, chemical and racing parts |
| Brass / Copper | Natural polish, nickel/chrome plating, lacquer, bead blast | Connectors, decorative hardware, electrical parts |
| Engineering Plastics (POM, Nylon, PEEK, ABS) | Bead blast, painting, laser engraving, vapor polish ( acrylic) – no anodize/plating | Insulators, gears, housings, medical and consumer parts |
Process Parameters
| Parameter | Standard Range |
|---|---|
| As-machined Roughness (default) | Ra 1.6μm - 3.2μm depending on tool strategy |
| Anodizing Thickness (Type II) | 5-25μm, color optional, no significant dimension change |
| Anodizing Thickness (Type III / hard) | 25-150μm, wear-resistant, grows from surface |
| Powder Coating Thickness | 60-120μm, RAL/Pantone matched |
| Electroplating Thickness | 5-25μm (decorative) to 50μm+ (engineering) |
| Polish Roughness (Mirror) | Ra ≤0.1μm; Satin Ra 0.2-0.8μm |
| Passivation / Electropolish | Thickness change negligible (<0.5μm); improves corrosion and cleanliness |
| Black Oxide | <0.5μm dimension change, mild corrosion resistance |
| Finish Added Lead Time | +3-5 days on top of machining |
Surface Finishes
Anodizing (Type II / Type III)
Electrochemical oxide layer on aluminum. Type II (5-25μm): corrosion resistance and color (black, red, blue, clear, gold). Type III/hard coat (25-150μm): extreme hardness and wear resistance. The layer grows from the surface, so it will not chip.
Powder Coating
Electrostatic thermoset powder cured at ~200°C. 60-120μm, RAL/Pantone color match, excellent weather, chip and chemical resistance. Ideal for outdoor and branded parts.
Electroplating (Chrome / Nickel / Zinc)
Metallic coating for appearance and corrosion/ wear resistance. Chrome for decorative brightness, nickel for wear, zinc for sacrificial corrosion protection. Thickness 5-25μm typical.
Passivation (Stainless)
Citric or nitric acid treatment that removes free iron and rebuilds the chromium oxide layer. Improves corrosion resistance with negligible dimension change – standard for stainless medical/food parts.
Electropolishing
Reverse-current polishing that smooths stainless to a bright, clean, low-microbial surface (Ra down to 0.1μm). Preferred for food, medical and hygienic applications.
Bead Blasting
Glass bead or aluminum oxide media produces a uniform matte texture (Ra 1.6-3.2μm), hides tool marks and improves coating adhesion. Common pre-step before anodize or paint.
Polishing (Satin / Mirror)
Mechanical polishing to a directional satin (Ra 0.2-0.8μm) or mirror (Ra ≤0.1μm) finish. Used for decorative, optical and medical surfaces.
Brushed Finish
Directional grain via abrasive belts for a consistent linear look on consumer electronics, architectural trim and decorative hardware.
Black Oxide
Conversion coating for steel providing a uniform black appearance and mild corrosion resistance with minimal dimension change. Common for tooling, fasteners and optics.
Painting (2K / UV)
Liquid paint systems with custom colors, soft-touch and matte/gloss options. Good for plastics and parts needing a non-metal color not covered by powder coat.
Laser Engraving / Etching
Permanent logos, serial numbers and markings directly on the part. No ink, no wear; ideal for traceability and branding.
Vapor / Flame Polish (Acrylic)
For acrylic and some clear plastics, a vapor or flame pass restores optical clarity on cut edges.
Design for Manufacturing (DFM)
- Specify the finish and its callout on the drawing – finish is a design requirement, not an afterthought
- Anodizing and plating add thickness to all exposed surfaces; adjust critical dimensions or mask those faces if clearance matters
- Sharp edges will round slightly during anodizing or electropolishing – design intentional edge breaks instead of relying on finish
- Mask threaded holes, bores and sealing surfaces when plating or anodizing would interfere with function
- Deburr and break edges before finishing so the finish sits on a clean surface
- Avoid trapped pockets and blind holes for electroplating – solution must drain and rinse freely
- For cosmetic parts, agree a sample finish swatch before production to lock color and texture
- Decide cosmetic vs functional finish early – it changes cost, lead time and inspection
Tooling & Capacity
| Type | Lead Time | Suitable For |
|---|---|---|
| In-house Anodizing Line | +3-5 days | Aluminum Type II/III, color and hard coat |
| Blasting & Polishing (in-house) | +1-2 days | Bead blast, satin/mirror polish, brush on most metals |
| Powder Coat & Paint Booth | +3-5 days | Aluminum, steel, some plastics; RAL/Pantone |
| Plating & Passivation (partner network) | +3-7 days | Chrome/nickel/zinc plating, stainless passivation, electropolish |
Quality Assurance
- Finish specification checked against drawing before the finishing operation begins
- Coating thickness measured with magnetic/eddy-current gauge or cross-section where specified
- Surface roughness verified with profilometer against the Ra target
- Adhesion checks (cross-hatch tape test) for paint and powder coat
- Appearance match to approved swatch for cosmetic finishes
- Masking verified so threads, bores and sealing surfaces stay functional
- Final inspection for color uniformity, coverage and defects per specification
- Lot traceability with inspection records retained per batch
Applications
- Anodizing: enclosures, brackets, heat sinks, optical and consumer hardware (corrosion + color)
- Powder coat: outdoor, automotive, furniture and branded parts (durability + color)
- Electroplating: decorative trim, connectors, fasteners, wear surfaces
- Passivation / electropolish: medical, food, pharmaceutical and hygienic parts
- Polish / brush: visible, optical and decorative surfaces
- Black oxide: tooling, fasteners, optical and instrumentation hardware
- Laser engraving: logos, serial numbers and traceability marks
- Painting: plastics and custom-color parts not suited to powder coat
Why Choose FHY Precision
One-stop finishing: machining plus most finishes coordinated in one place, fewer hand-offs and shorter lead time
Broad menu: 12+ finishing options covering corrosion, wear, appearance and hygiene
Free DFM analysis: our report flags finish-related design issues (masking, thickness, edge break) before production
Sample-first: we can supply a finish swatch or T1 sample so color and texture are approved up front
Material expertise: we recommend the right finish for aluminum, stainless, steel, titanium, brass or plastic
Measured quality: coating thickness and roughness verified, with adhesion and appearance checks
Factory-direct China pricing backed by disciplined process control in our workshop
Traceable: finish specifications and inspection records retained per production batch
FAQ
1. How do I choose the right finish for my part?
Start from the base material and the job the finish must do. For aluminum appearance + corrosion, anodizing (Type II color, Type III hard) is the default; for durable color on any metal, powder coat. For stainless hygiene/corrosion, passivation or electropolish. For decorative brightness on steel or brass, plating. For optical/visible surfaces, polish or brush. We summarize the trade-offs in the free DFM report and can mail you swatches.
2. Does anodizing or plating change my dimensions?
Anodizing Type II adds 5-25μm and Type III adds 25-150μm, all grown from the surface, so it will not chip but it does affect clearances on every exposed face. Plating adds similar microns. If a bore or thread must stay functional, tell us to mask it or machine it after finishing. Passivation and black oxide change dimensions by less than 0.5μm.
3. What roughness can I get?
As-machined is Ra 1.6-3.2μm. Bead blast keeps you in that range with a matte look. Satin polish reaches Ra 0.2-0.8μm and mirror polish Ra ≤0.1μm. Electropolished stainless can also reach ~0.1μm. Tell us the Ra target and we will select the process.
4. How much does finishing add to cost and lead time?
Most finishes add 3-5 days. Anodizing and powder coat are economical; plating and electropolishing cost more because of chemistry and handling. Polishing cost scales with the Ra target (mirror costs more than satin). We itemize finishing in the quote so there are no surprises.
5. Can you match a specific color?
Yes. Powder coat and paint are matched to RAL or Pantone; anodizing offers standard colors (black, clear, red, blue, gold) and custom dyes on request. We recommend approving a physical swatch before a production run.
6. Can you mask threads, bores or sealing surfaces?
Yes. We mask threaded holes, bores, sealing faces and any feature where buildup would affect function, then verify the mask after finishing. Flag these clearly on the drawing or in the DFM review.
7. Do you provide sample finishes before production?
Yes. For cosmetic finishes we can supply a swatch or a T1 sample part so color and texture are approved before the full run. This avoids rework on large batches.
8. Which finishes work on plastics?
Plastics cannot be anodized or metal-plated by the usual processes. For plastics we offer bead blast, painting (2K/UV), laser engraving and vapor/flame polish for clear acrylic. Tell us the resin and we will recommend a compatible finish.
9. Can you engrave my logo or serial number?
Yes. Laser engraving marks logos, part numbers and serials directly on the part – permanent, ink-free and ideal for branding and traceability.
10. Do you ship finished parts internationally?
Yes, worldwide. Samples by express (3-7 business days); volume by air or sea freight (2-6 weeks). Finished parts are packed with protection appropriate to the finish (e.g. interleaving for polished or anodized surfaces) plus anti-corrosion measures for transit.
11. What is the default finish if I do not specify one?
As-machined. The part ships with visible tool marks at a standard roughness of about 3.2μm Ra – the fastest and cheapest option, and appropriate for internal or non-cosmetic parts. If you have cosmetic surfaces, sealing faces or bearing surfaces, call them out on the drawing or we will treat everything as non-critical. Saying 'no finish required' on a drawing is a decision, not a neutral choice – we recommend confirming which surfaces matter.
12. What Ra value should I put on my drawing?
A practical guide: Ra 3.2μm (63 microinch) for general parts, Ra 1.6μm for sliding or light sealing surfaces, Ra 0.8μm for bearing and seal faces, Ra 0.4μm and below only for optical or precision functional surfaces. Every tighter callout adds machining passes, inspection time and cost. The most common mistake we see is blanket-tolerancing the whole part at Ra 0.8 when only one face needs it – specifying finish only where function demands it is free money.
13. Which finish gives the best corrosion resistance?
It depends on the base metal. For aluminum, Type III hard anodize or chromate conversion; for stainless steel, passivation (with electropolishing for hygienic or bright surfaces); for carbon and alloy steel, electroless nickel plating, zinc plating or powder coating. Powder coating works on almost any metal and handles outdoor UV exposure well. There is no single best finish – the right answer starts with your service environment: indoor cosmetic, outdoor, marine or chemical.
14. How much lead time does each finish add?
Bead blasting and brushing add less than a day. Anodizing and plating typically add 2-3 days. Powder coating adds 1-2 days including cure. Mirror polishing can add up to 5 days because it is manual work with multiple inspection stages. Finishing usually runs in parallel with other orders in the queue, so the real calendar impact depends on what else is in the line – we will give you a realistic combined date at quotation, not a best case.
15. Can I use black oxide on food or medical equipment?
No. Black oxide is an industrial finish for tools, fasteners, firearms and machinery. It provides only mild corrosion resistance and must be sealed with oil or wax, which makes it unsuitable for food contact, medical use or anything that will be cleaned with solvents. For food or medical stainless parts, specify passivation; for food-safe colored steel, powder coating with a food-contact-approved formulation. If your part touches food, tell us early so the finish spec is right the first time.
16. Which finishes hold up best outdoors?
Powder coating and Type III hard anodize are the two workhorses for outdoor service – both resist UV degradation, weathering and temperature swings. For steel, hot-dip galvanizing under powder coating (duplex system) gives the longest life in aggressive environments. Avoid bright decorative platings outdoors unless specified for exterior use; standard chrome plating can dull and pit under UV and salt. For marine exposure, add thickness to the spec and ask about sealing.