Will anodizing change my critical dimensions?

Yes. For planning, treat diameter/width change approximately equal to the coating thickness (T). Mask H7/H8 fits or plan post-finish sizing (ream/hone/lap).

Which finishes are electrically conductive?

Chromate conversion (Alodine) and electroless nickel (EN) are conductive. Anodize and powder coat are insulating unless masked.

How do I specify finishing on drawings?

List finish type and standard, thickness range, color/gloss, masked surfaces, and mark critical dimensions as Post-Finish. Add notes for eddy-current thickness and Pre/Post CMM inspection.

Can tight bores (±0.01 mm) be achieved after finishing?

Yes—by masking or post-finish sizing. Provide the target fit class (e.g., H7) and we will plan ream/hone/lap accordingly.

Why do black anodize lots sometimes look different?

Alloy and surface prep matter. We unify blasting, control dye and sealing windows, and track ΔE (D65/10°) with a realistic production target of ΔE ≤ 2.0 on visible faces.

Is EN uniform in blind holes and pockets?

EN is very uniform; for extreme aspect ratios we optimize orientation and solution circulation and may increase nominal thickness to secure minimums.

What documents ship with finished parts?

Finish certificates, thickness logs, Pre/Post CMM on defined features, optional ISO 9227 salt-spray/adhesion/hardness, RoHS/REACH, and packing photo proof.

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Surface Finishing Guide | Processes · Materials · Industry Case Studies

Practical, standards-based guidance to help R&D, engineering, and procurement teams select and implement the right surface finishing solutions across CNC machining, molding, 3D printing and sheet metal.

Reliability & Consistency

Stable processes and verified parameters deliver repeatable cosmetic and functional results across batches, backed by our quality assurance system.
Compliance (RoHS / REACH / ISO)

Chemistries and documentation aligned with global regulations and ISO-based quality systems, including ISO 9001 and IATF 16949 requirements for automotive.
Controlled Lead Times

Capacity planning and standardized routings help keep prototypes and production runs on schedule.
Traceable Quality

End-to-end records for thickness, hardness, and corrosion testing enable full auditability and can be reviewed during your free DFM & surface finishing check.

Why this Surface Finishing Guide

Pick CNC finishes without guesswork.

Surface finishing is the family of post-machining treatments applied to CNC parts to modify the outermost layer for performance or appearance. After CNC cutting leaves tool marks and raw metal surfaces, finishing improves corrosion resistance, wear life, friction behaviour, cosmetics, and prepares parts for assembly or sterilization.

This guide puts common metal and plastic finishes in one place so you can choose a process, predict how it will change your dimensions, and move to production with confidence.

Typical use cases

You need realistic tolerances after anodizing, EN, passivation, or polishing.
Drawings follow GB / JIS / ASTM standards and must stay equivalent after finishing.
Parts move between machining, molding, and sheet metal and must look consistent.

What you’ll get here

Clear explanations by process: anodize, plating, chem film, painting, polishing, and more.
“Fit after finish” rules so threads, bores, and sealing faces work the first time.
Checklist style tips you can attach to RFQs and inspection plans.

Surface Finishing Guide showing anodized and coated CNC parts — Surface finishing options for CNC parts, including anodized and coated samples.

Precision CNC Technical-Article Guide

Explore our comprehensive library of technical articles and manufacturing guides. Deep dives on design rules, advanced materials, and high-performance finishing.

Overview of Precision CNC Surface Finishing Types

Anodizing

Use this section for realistic guidance on aluminum CNC parts regarding thickness, dimensional change, and corrosion resistance. The default finish for protective/decorative machining.

• Type II/III Process
• Aerospace Specs
• RoHS Compliance
• Visual Cosmetics

Anodizing creates a controlled Al₂O₃ ceramic layer. It is used extensively in 5-axis CNC machining to enhance durability and aesthetics.

Thickness Range 7–20 μm

Alloy Compatibility 1xxx–7xxx

High precision CNC machined aluminum enclosure with Type II anodizing

Performance

Corrosion: 300+ hrs Salt Spray (ISO 9227).
Hardness: Type III for extreme wear.
Visuals: High-grade dye saturation.
Dielectric: Superior electrical insulation.

Cost & Lead Time

Budget: Type II ($) / Type III ($$).
Efficiency: High nesting density.
Prototypes: 3–5 Business Days.
Production: Scalable 10-day cycles.

Compliance

Standards: RoHS & REACH Compliant.
Health: Cr(VI)-free sealing options.
Environment: pH-balanced processing.
Quality: ASTM B117 / MIL-A-8625.

Hard Anodizing

Ideal for aluminum components facing heavy wear, high loads, or sliding contact. Type III Hardcoat provides the ultimate industrial protection where decorative Type II fails.

As an electrochemical process, Hard Anodizing (Type III per MIL-A-8625F) creates a dense Al₂O₃ ceramic layer. Used extensively in Rapid Tooling and high-performance hydraulics.

Hardcoat Thickness 25–125 μm

Applicable Materials 1xxx–7xxx

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Type III Spec

Performance Data

Hardness: 350–500 HV (Steel equivalent)
Corrosion: 1000+ hrs Salt Spray (ASTM B117)
Wear: 10x improvement over bare aluminum
Thermal: Operational stability up to 400°C

Production Logistics

Cost Factor: $$ (Mid-range industrial)
Prototypes: 3–5 Business Days
Batching: High-density nesting support
Expedited: 48-hour rush available

Compliance

Environment: RoHS & REACH Compliant
Standard: MIL-A-8625 / ASTM B117
Safety: Cr(VI)-free modern sealing
Process: Low-temp (0-5°C) sulfuric bath

Black Oxide

A low-cost, dimensionally neutral conversion coating for steels and brass. Ideal for tools, fasteners, and precision mechanical hardware requiring mild, oil-assisted protection.

This chemical reaction forms a thin magnetite (Fe₃O₄) layer, commonly used for its aesthetic matte finish and reduced light reflection in Swiss lathe and high-precision turning projects.

Layer Thickness < 1.0 μm

Applicable Materials Steels, Copper, Brass

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Precision View // 0.2–0.8 μm

Performance Metrics

Corrosion: 24–96 h NSS (with oil/wax seal)
Dimensional: Zero-change (ideal for tight fits)
Appearance: Deep matte to semi-gloss black
Conductivity: Remains electrically conductive
Temperature: Stable up to approx. 300°C

Logistics & Compliance

Cost & Lead Time

Relative Cost: $ (Most economical option)
Standard Lead: 2–3 Business Days

Environmental Standards

Compliance: RoHS & REACH Compliant
Process: Cr(VI)-free chemical conversion

Electroless Nickel (EN)

Essential for achieving a perfectly uniform metallic coating on complex geometries, internal passages, and deep bores where traditional electroplating fails to deposit evenly.

An auto-catalytic chemical process that deposits a nickel-phosphorus alloy without external current. Ideal for high-precision machined castings and fuel system components.

Deposition Rate 10–25 μm/h

Base Materials Steels, Al, Copper

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Auto-Catalytic Deposit

Performance Data

Corrosion: >1000h NSS (High-P alloys)
Hardness: 900–1100 HV (Post-heat treat)
Friction: Approx. 0.1 with PTFE co-deposit
Thermal: Operational stability up to 400°C

Cost & Logistics

Relative Cost: $$ (Mid-range industrial)
Lead Time: 3–5 Business Days
Drivers: Layer thickness & Heat treatment
Efficiency: Uniformity reduces re-machining

Compliance

Environment: RoHS & REACH Compliant
Process: Cr(VI)-free chemical reaction
Safety: Controlled phosphine filtration
Quality: MIL-C-26074 / ASTM B733

Nickel Electroplate

A versatile bright decorative finish or functional barrier layer. Essential for trim parts, connectors, and precision molds requiring both corrosion resistance and aesthetic appeal.

Electrolytic deposition of nickel metal provides a mirror-like bright or semi-bright finish. Often serves as a critical pre-coat for machined castings and high-wear automotive components.

Standard Thickness 5–30 μm

Applicable Materials Steel, Al, Copper

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Electrolytic Finish