A practical guide to CNC surface finishes — from as-machined to anodizing, powder coating, and more.
Surface finish is more than appearance. It affects corrosion resistance, wear tolerance, aesthetic appeal, and even part function. This guide covers the most common surface finishing options for CNC machined parts.
1. As-Machined (Standard)
The default finish after CNC machining. Tool marks are visible, and surface roughness typically ranges from Ra 1.6–3.2 μm.
- Best for: Internal parts, prototypes, functional test pieces
- Cost: Included in standard pricing
- Lead time: No additional time
2. Bead Blasting
Small glass beads are blasted onto the surface to create a uniform matte finish. Reduces the appearance of tool marks.
- Best for: Aesthetic improvement, uniform appearance
- Cost: Low additional fee
- Lead time: +1 day
3. Brushed Finish
Linear brushing creates a directional satin finish. Common on stainless steel and aluminum.
- Best for: Consumer products, architectural parts, medical devices
- Cost: Medium
- Lead time: +2 days
4. Polished Finish
Mechanical polishing produces a smooth, reflective surface. Achieved through progressive buffing compounds.
- Best for: Decorative parts, optical components, high-end products
- Cost: Higher
- Lead time: +3–5 days
5. Anodizing (Aluminum)
Electrochemical process that creates a durable oxide layer. Available in clear, black, color, and hard coat anodizing.
- Clear: Maintains natural aluminum look
- Black: Popular for industrial and consumer products
- Color: Color dye added to oxide layer
- Hard coat: Thicker layer for extreme wear resistance
- Best for: Aluminum parts requiring durability, appearance, or corrosion resistance
- Cost: Medium to high
- Lead time: +3–7 days
6. Powder Coating
Dry powder applied electrostatically and cured under heat. Provides a durable, uniform coating in many colors.
- Best for: Outdoor parts, automotive, furniture
- Cost: Medium
- Lead time: +5–7 days
7. Zinc Plating
Electroplated zinc coating provides corrosion resistance. Available as plain, black, or trivalent passivation.
- Best for: Steel parts, fasteners, industrial components
- Cost: Low to medium
- Lead time: +3–5 days
8. Black Oxide
Chemical conversion coating that turns the surface black. Common on steel and stainless steel.
- Best for: Tools, dies, fasteners, cosmetic dark finish
- Cost: Low
- Lead time: +2–3 days
9. Electroless Nickel Plating
Uniform nickel-phosphorus coating applied without electricity. Provides excellent wear and corrosion resistance.
- Best for: Hydraulic parts, molds, gear surfaces
- Cost: Higher
- Lead time: +5–7 days
How to Choose the Right Surface Finish
Consider these factors:
- Environment: Will the part be outdoors, in moisture, or exposed to chemicals?
- Wear: Will the part experience friction or physical contact?
- Appearance: Is cosmetic appearance important?
- Cost sensitivity: Some finishes add significant cost — balance need vs. budget
- Tolerance impact: Some coatings change dimensions — account for this in design
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