Finishes
CNC Surface Finishes
A plain map of every finish you can put on a machined part, and how to pick one
CNC surface finishes are the treatments a part gets after it comes off the machine, from bare as-machined metal to bead blast, anodize, powder coat, passivation, plating, and a polished or stonewashed look. Most of these metal finishing options change thickness, threads, bores, or conductivity, so the finish is called out on the print and quoted with the part, and critical features get masked. The right finish is the one that matches what the part has to do: a cheap matte for an EDC piece, a hard wear layer for a sliding surface, or nothing at all for a hidden bracket. Tell us what the part is and how it has to look or hold up, and a real person sends back a quote in 24-48 hours.
Updated June 2026
Start with as-machined and bead blast
Every part starts as-machined, the default. It’s the lowest cost option and it leaves faint, visible tool marks. For internal parts, functional brackets, and prototypes where looks don’t matter, bare as-machined metal is often the right and cheapest answer, so don’t pay for a finish a hidden part will never show off.
Bead blast is the next step up and the usual cosmetic baseline. The part is media-blasted to an even matte that hides tool marks, which is also why it’s the standard prep before anodize or coating. If you want “no visible tool marks” on a cosmetic or consumer part, bead blast (then optionally anodize or coat) is usually what you’re reaching for, not as-machined.
Anodize, powder coat, and passivation
Anodize is for aluminum: an integral oxide layer grown into the surface. Type II comes in clear, black, and dyed colors for a cosmetic, corrosion-resistant finish, and Type III hardcoat steps up wear resistance for sliding surfaces. It’s the standard callout on most aluminum parts, and the depth is on the dedicated anodizing page.
Powder coat is a thick, tough, opaque color coating that’s heat-cured onto the part. It gives bold colors and real outdoor durability and works on steel, stainless, and aluminum, covered on the powder coating page. Passivation is the stainless answer: a chemical bath that removes free iron and restores corrosion resistance with no dimensional or color change, a cheap callout that’s standard practice for food, fluid, and outdoor parts. See the passivation page for the spec detail.
Cosmetic and EDC looks
When a part is meant to be seen and handled, the finish does the talking. Brushed gives a directional grain and polished goes near-mirror, both for parts where looks matter. Stonewashed and tumbled parts are run with media for a uniformly deburred, softly worn look that’s popular on EDC pieces and on titanium.
Plating and conversion coatings round out the metal finishing options. Zinc, nickel, or black oxide on steel add corrosion resistance plus a dark look, while chromate and alodine conversion coatings keep aluminum conductive, which anodize doesn’t. For cosmetic enclosures and covers, a bead-blast-then-anodize combo is a common, clean default.
How to choose, and why it goes on the print
Pick the finish by what the part has to do, not by the longest menu. Ask three things: does it need to look finished, does it need corrosion or wear protection, and does it need to stay conductive or grounded. A hidden internal part can stay as-machined; a handled cosmetic part wants bead blast or tumbling; a sliding surface wants Type III; a stainless fluid part wants passivation.
The reason it matters at quote time: most finishes add or affect thickness, threads, bores, and conductivity, so a press fit or a tapped hole can shift if the coating isn’t planned for. That’s why the finish is specified on the print and quoted with the part, and why critical features get masked. Parts come back finished and every part is inspected before it ships, so what you spec is what you get.
Questions
Before you send a job.
01 Which CNC surface finish is the cheapest?
As-machined is the cheapest, since it’s just the bare part with no extra step. It leaves faint tool marks, so it’s best for internal, functional, or prototype parts where looks don’t matter. For a clean look on a budget, bead blast is the next step up and still inexpensive.
02 How do I get rid of visible tool marks?
Tool marks are evened out with bead blast, which gives a uniform matte, or with tumbling for a softly worn look. Either one can stand on its own or act as prep before anodize or coating. As-machined is the one finish that does still show faint marks, so it’s not the choice for cosmetic parts.
03 Do finishes change the part dimensions?
Most do. Anodize, powder coat, and plating add or affect thickness, threads, bores, and conductivity, while passivation changes neither size nor color. That’s why the finish is called out on the print and quoted with the part, and why critical features get masked so a press fit or tapped hole still works.
04 What finish keeps aluminum electrically conductive?
Anodize is an oxide layer, so it’s not conductive. When a part has to stay grounded or conductive, chromate or alodine conversion coatings are the callout instead. Note it on the print and it gets quoted and masked accordingly.
05 Can I get a finish on a stainless part?
Yes. The standard stainless callout is passivation, which restores corrosion resistance without changing size or color. Bead blast, brushed, and polished looks are also common on stainless, and the finish is specified on the print and quoted with the part.
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