Surface Finishes for CNC, Sheet Metal, Plastic and Composite Parts
A part's surface finish is often as important as its dimensional accuracy — it affects cosmetics, corrosion resistance, friction, electrical insulation, paint adhesion and cleanability. At SkillsProto, we manage surface finishing through in-house capability and audited partner facilities, all rolled into a single quote and lead time.
This page is the master reference for the finishes we offer across all processes.
Finishes for machined parts
| Finish | Description | Typical Use |
|---|---|---|
| As-milled / as-turned | Direct from machine tool marks visible | Functional, hidden parts |
| Bead blast (matte) | Uniform matte from glass bead blasting | Cosmetic aluminium, hides minor tool marks |
| Satin brush | Linear scratch pattern | Architectural and premium cosmetic |
| Polished (mirror) | High gloss, near-mirror | Premium cosmetic, food contact |
| Anodising — Type II | Sulphuric acid, decorative colour | Aluminium enclosures, brackets |
| Anodising — Type III (hard) | Thicker, wear-resistant | Aluminium wear surfaces |
| Chromate conversion (Alodine) | Thin protective film | Paint prep, corrosion protection |
| Powder coating | Dry powder, cured, durable colour | Steel and aluminium enclosures |
| Electroless nickel | Nickel-phosphorus plating | Steel wear and corrosion resistance |
| Zinc plating / galvanising | Zinc coating | Steel corrosion protection |
| Chrome plating (Cu-Ni-Cr) | Decorative chrome over underlayers | Decorative hardware, premium parts |
| Black oxide | Conversion coating for steel | Mild corrosion resistance, low gloss |
| Passivation | Citric / nitric acid | Stainless steel corrosion resistance |
| Electropolishing | Electrochemical smooth | Stainless hygienic, medical, food |
Finishes for sheet metal
| Finish | Description | Typical Use |
|---|---|---|
| Mill finish | As-cut, mill scale on steel | Hidden parts, weldments |
| Bead blasted | Matte uniform | Prep for paint |
| Powder coated | Durable colour | Enclosures, brackets, panels |
| Wet painted | High-gloss colour, primer + base + clear | Premium panels, colour matching |
| Anodised | Aluminium only | Aluminium corrosion + colour |
| Zinc plated / galvanised | Steel only | Steel corrosion protection |
| Brushed stainless | Linear scratch on stainless | Architectural, decorative |
| Silk-screen / pad print | Logos and markings | Labels, scales, instructions |
| Laser marking | Permanent dark mark on metal | Part numbers, lot codes, branding |
Finishes for plastic parts (moulded / cast / 3D printed)
| Finish | Description | Typical Use |
|---|---|---|
| As-moulded | Direct from tool surface | Functional, hidden parts |
| SPI-A1/A2/A3 | High-gloss polish grades | Premium cosmetic |
| SPI-B1/B2/B3 | Medium gloss | General cosmetic |
| SPI-C1/C2/C3 | Fine matte | Hides minor flow lines |
| SPI-D1/D2/D3 | Rough texture | Heavy-duty or grip surfaces |
| VDI 3400 textures | German standard textures | Specific texture references |
| Painting | Colour matched | Cosmetic plastic parts |
| Pad printing / silk-screen | Graphics, labels | Logo, scales, text |
| Chrome plating (on plastic) | Premium decorative | Automotive interior trim |
| Soft-touch coating | Rubber-like feel | Grips, premium consumer |
| UV-resistant clear coat | UV protection | Outdoor plastic parts |
Finishes for composite parts (FRP / carbon fibre / glass fibre)
| Finish | Description | Typical Use |
|---|---|---|
| As-cured | Direct from mould | Hidden structural |
| Gel coat (colour) | Coloured durable surface | GRP body panels, marine |
| Clear coat (gloss / matte) | Shows carbon weave | Carbon fibre cosmetic |
| Paint | Colour matched | Body panels, covers |
| Machined after cure | CNC trim, drilled holes | Precision edge finish |
| Metal inserts | Bonded / co-cured | Mounting points |
How we choose a finish
When you send an RFQ, we recommend finishes based on:
- Function — wear surface, sealing surface, cosmetic, hidden.
- Environment — indoor, marine, outdoor, chemical.
- Material — aluminium, steel, plastic, composite.
- Budget — some finishes (anodising, plating, painting) add cost and lead time.
If you have a target finish in mind, tell us; we will quote to your spec.
Frequently Asked Questions
Q1: What is the cheapest cosmetic finish? A: Bead blast — fast, low cost, uniform matte appearance.
Q2: What is the most durable corrosion-resistant finish for aluminium? A: Type III hard anodising for wear + corrosion; powder coating for general exterior use.
Q3: Can you match a RAL or Pantone colour? A: Yes — through anodising, powder coating or wet painting. Send the reference and we will include colour match in the quote.