Surface Finishes for CNC Machining Parts
RpProto provides a wide range of surface finishing services to supplement our CNC Prototyping, such as Anodizing, Bead Blasting, Powder Coating, Electroplating.
As-Machined
Default finish · No post-processing required
Ra Range
0.8 – 3.2 μm
Adds Material
No
Color Options
None
Cost Premium
None
As-machined parts come directly off the CNC mill or lathe with visible tool marks and no additional processing. The surface shows the tool path pattern from the cutting operation.
This finish offers the tightest dimensional tolerances of any option, since no material is added or removed post-machining. It is the preferred choice for functional internal components, structural brackets, and parts that will be assembled inside a system where surface appearance is not critical.
Best for: Tight-tolerance parts, internal components, prototypes, cost-sensitive production runs.
Anodizing
Type II (Standard) · Type III (Hard Coat)
Ra Range
0.4 – 1.6 μm
Thickness
4–125 μm
Color Options
Yes (many)
Cost Premium
Medium
Anodizing is an electrochemical process that converts the metal surface into a durable, corrosion-resistant aluminum or titanium oxide layer.
Type II (Standard): Produces coatings 4–25 μm thick. Ideal for decorative and light functional parts. Easily dyed in a wide range of colors. Good corrosion and moderate wear resistance.
Type III (Hard Coat): Produces dense coatings up to 125 μm thick (standard 50 μm). Dramatically higher wear and abrasion resistance. Preferred for aerospace, hydraulic, and military components.
Best for: Aluminum consumer electronics, aerospace structural parts, medical devices, any part needing color coding.
Bead Blasting
Shot blasting · Media blasting
Ra Range
0.8 – 2.0 μm
Adds Material
None
Color Options
None
Cost Premium
Low
Bead blasting propels small spherical glass or ceramic beads at the part surface using compressed air. The impact of the beads creates a uniform, consistent matte or satin texture while cleaning the surface and removing any remaining tool marks.
Unlike shot peening, bead blasting’s primary purpose is aesthetic — creating a clean, non-reflective uniform surface. It is frequently used as a pre-treatment before anodizing or powder coating to ensure an even base texture.
Best for: Consumer-facing aluminum parts, pre-treatment before anodizing, parts needing a clean uniform texture without being mirror-polished.
Powder Coating
Electrostatic spray · Oven-cured polymer
Thickness
50 – 150 μm
Adds Material
Yes
Color Options
Unlimited (RAL)
Cost Premium
Medium
Powder coating applies electrostatically-charged dry polymer powder to a grounded metal part. The particles adhere to the surface, then the part is baked in an oven (typically 180–200°C), fusing the powder into a smooth, hard, uniform coating.
The result is a thicker, more impact-resistant coating than liquid paint, with excellent color consistency and edge coverage. It provides strong corrosion and UV resistance. Parts are often bead blasted before powder coating for best adhesion.
Best for: Industrial equipment, outdoor fixtures, brackets, housings — any metal part requiring durable color and corrosion protection.
Electroplating
Nickel · Chrome · Zinc · Gold · Silver
Ra Range
0.1 – 0.8 μm
Thickness
1 – 50 μm
Color Options
Limited (by metal)
Cost Premium
Medium–High
Electroplating deposits a thin metal layer onto a part’s surface using an electrolytic bath. The part is submerged in a solution containing dissolved metal ions, and an electric current causes those ions to plate onto the substrate.
Common plating types include nickel (wear/corrosion resistance), chromium (hardness and appearance), zinc (sacrificial corrosion protection), and gold or silver (electrical conductivity and contact reliability). Plating thickness is precisely controllable from 1–50 μm.
Best for: Electronic connectors, fasteners, decorative hardware, parts requiring specific surface conductivity.
Brushing
Mechanical brushing · Directional texture
Ra Range
0.4 – 1.6 μm
Adds Material
No
Color Options
None
Cost Premium
Low
Brushing uses abrasive belts or rotating wire brushes to create fine, parallel lines across the metal surface in a single direction. The result is a satin-like, linear texture commonly associated with premium consumer electronics and appliances.
Unlike bead blasting (which produces a random, isotropic texture), brushing creates a consistent directional pattern. It does not add a protective layer — it is a purely aesthetic finish, though it does slightly reduce reflectivity and hide minor surface imperfections.
Best for: Decorative panels, consumer electronics housings, architectural hardware, premium product enclosures.
Polishing
Mirror finish · Electropolishing · Mechanical
Ra Range
0.025 – 0.4 μm
Removes Material
Yes (slight)
Color Options
Natural metal only
Cost Premium
High
Polishing uses progressively finer abrasives or electrochemical processes to achieve extremely smooth surfaces approaching a mirror finish. Mechanical polishing uses abrasive compounds on buffing wheels; electropolishing uses an electrochemical bath to dissolve microscopic peaks and produce an ultra-clean, bright surface.
Electropolishing also passivates stainless steel surfaces simultaneously, making it highly valued in medical and food processing applications. It can achieve Ra values as low as 0.025 μm.
Best for: Medical implants, optical components, food-grade equipment, high-end decorative parts, sealing surfaces.
Ready to Apply a Surface Finish to Your Parts?
Upload your CAD files for an instant quote. Our engineers review every order for finish compatibility and DFM feedback before production.