Common post-machining finishes — anodizing, plating, passivation, bead blast, and more — available and coordinated as turnkey options when ordered with your parts.
Use this guide when you are choosing a post-machining finish and need to understand appearance, corrosion/wear behavior, and dimensional impact before you freeze the drawing.
Surface finishes change appearance, corrosion resistance, wear, cleanability, and final size. Always state the finish on the drawing, note masked surfaces, and allow for growth or material removal on fits and threads.
Common finishes are available and coordinated when ordered with the machining job (turnkey when scoped on the PO). Specs such as ASTM anodize classes or ASTM A967 passivation apply when called out on the RFQ/PO — do not assume every process is performed in-house without project confirmation.
If no finish is specified, expect a machined surface often around Ra 3.2 µm or finer depending on the toolpath. Call out cosmetics when they matter.
| Type | Thickness | Appearance | Wear / hardness | Typical uses |
|---|---|---|---|---|
| Type II (sulfuric) | 5 – 25 µm | Clear or dyed (black, blue, red, gold, …) | Moderate | Enclosures, trim, consumer and industrial cosmetics |
| Type III (hardcoat) | 25 – 100 µm | Dark gray/bronze; dye limited | Excellent (high hardness) | Wear surfaces, robotics, high-duty parts |
| Type I (chromic) | 1 – 5 µm | Clear, thin; limited dye | Low — corrosion focus | Fatigue-sensitive or welded structures when specified |
Anodize grows roughly half the oxide thickness outward. Hardcoat can move dimensions on the order of ~0.05 mm per surface. Mask threads and precision bores, or machine undersize before coating.
| Media | Surface | Typical Ra | Typical use |
|---|---|---|---|
| Glass bead | Smooth satin matte | 1.0 – 2.5 µm | Aluminum, stainless, titanium cosmetics |
| Aluminum oxide grit | Aggressive texture / anchor | 3.2 – 6.3 µm | Steel prep for paint or powder |
| Ceramic bead | Fine matte; longer media life | 1.6 – 3.2 µm | Hard alloys needing consistent prep |
Blasting can close fine holes (below 0.5 mm) and embed media in soft stock — plug or mask sensitive features. It is often used before anodize or powder coat to improve adhesion.
Removes free iron and restores chromium-rich oxide. Negligible dimensional change. Common baths: nitric or citric per ASTM A967 / AMS 2700 when specified. Free-machining grades (e.g. 303) may respond less uniformly than 304/316.
Electrostatic powder cured under heat — typically 50–150 µm. Strong chip and UV resistance outdoors. Mask threads and precision fits; not suited to fine-pitch fasteners without clearance design.
Electrochemical material removal that brightens and cleans stainless (and selected other alloys). Improves cleanability; removes ~5–40 µm. Sharp edges round; leave stock on critical sizes.
If no finish is specified, expect a machined surface often around Ra 3.2 µm or finer depending on the toolpath — call out cosmetics when they matter.
| Finish | Substrates | Key characteristics |
|---|---|---|
| Black oxide | Steel / stainless | Minimal size change; matte black; mild corrosion resistance (often oiled) |
| Electroless nickel | Steel, aluminum, copper alloys | Uniform thickness; wear/corrosion; solderable |
| Zinc plating | Carbon steel | Sacrificial corrosion protection; chromate options |
| Brushing / graining | Stainless, aluminum | Directional cosmetic grain; hides fingerprints |
| Laser mark / engrave | Most metals and plastics | Permanent IDs, logos, serialization |
| Material | Common finishes | Primary purpose |
|---|---|---|
| Aluminum 6061/7075 | Type II/III anodize, blast, powder | Corrosion, wear, cosmetics |
| Stainless 304/316 | Passivation, electropolish, blast, black oxide | Corrosion, cleanability, cosmetics |
| Carbon / alloy steel | Black oxide, zinc, EN, powder | Rust protection, wear, industrial look |
| Titanium | Color anodize, passivation, blast | ID color, oxide stability, matte prep |
| Copper / brass | EN, lacquer, polish | Tarnish control, wear, conductivity care |
| Engineering plastics | As-machined, selective blast / polish | Texture and optics — avoid metal coating assumptions |
| Finish | Typical change | Design advice |
|---|---|---|
| Type II anodize | + 2.5 – 12.5 µm outward class | Allow for fits; mask threads |
| Type III hardcoat | + 12.5 – 50 µm class (~0.05 mm possible) | Machine undersize; avoid sharp corners that build thick |
| Powder coating | + 50 – 150 µm | Mask precision bores and threads |
| Electroless nickel | + 5 – 25 µm typical; uniform | Can machine to size after plating when needed |
| Passivation | Negligible (under 1 µm) | No allowance needed |
| Electropolishing | − 5 – 40 µm removal | Leave stock; expect edge rounding |
As-machined tool marks ship when the buyer expected matte blast or dyed anodize — rework or scrap follows if the drawing was silent.
Hardcoat (~0.05 mm per surface class growth) or powder coat closes diameters when CAD was never compensated and threads were not masked.
Calling Type II anodize on steel, or passivation on aluminum, forces mid-quote process changes. Match finish to material early.
Critical sizes measured before vs after finish disagree unless the drawing states which condition applies ([Tolerance Standards](/precision-tolerance-standards/)).
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