A Guide to Surface Finishes for CNC Machined Parts

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In the world of CNC machining, the journey from a raw block of material to a finished part doesn't end with the last cutting tool path. The surface finish is a critical final step that profoundly impacts a component's functionality, durability, and aesthetics. Choosing the right finish is not merely a cosmetic decision; it's an engineering one that can determine the success of your product. This guide outlines the common surface finishes available for CNC machined parts.


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AsMachined
This is the standard finish straight from the CNC machine, with visible tool marks. It is the most costeffective and fastest option, suitable for noncritical surfaces, functional prototypes, and parts where surface texture is not a concern. Tolerances are held precisely, but the surface may be prone to minor imperfections.

Bead Blasting
This process involves propelling a stream of small glass beads at the part's surface. It creates a uniform, matte, or satin texture that effectively hides tool marks and minor scratches. Bead blasting is excellent for improving visual appeal and providing a consistent, nonreflective surface, often used as a pretreatment for anodizing.

Anodizing (Type II & III)

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Anodizing is an electrochemical process that converts the metal surface into a durable, corrosionresistant, anodic oxide layer.
Type II (Decorative): Provides good corrosion and wear resistance and is available in a wide range of colors, making it popular for consumer electronics and architectural components.
Type III (Hard Anodizing): Creates a much thicker and harder coating, offering superior abrasion resistance and dielectric strength, ideal for military, aerospace, and highwear industrial applications.



Powder Coating
This finish involves applying a dry powder electrostatically and then curing it under heat to form a hard, protective skin. Powder coating is known for its exceptional durability, corrosion resistance, and vast selection of colors and textures (e.g., glossy, matte, wrinkled). It is typically applied to larger parts and offers excellent impact resistance.

Electroplating
Processes like nickel and chrome plating deposit a thin layer of metal onto the part. Nickel plating offers excellent corrosion resistance and hardness, while chrome plating provides a bright, reflective, and very hardwearing surface. These finishes are often used for both decorative purposes and to enhance functional properties like lubricity and wear resistance.

Making the Right Choice
The optimal surface finish depends on your part's application:
Aesthetics: Consider bead blasting, anodizing, or painting.
Wear & Corrosion Resistance: Hard anodizing, powder coating, or electroplating are excellent choices.
Dimensional Stability: Be aware that coatings like anodizing and powder coating add thickness. "Asmachined" is best for critical tolerances.

Partnering with a manufacturer that offers a comprehensive suite of finishing options is crucial. At our company, we provide expert guidance and inhouse finishing services to ensure your CNC machined parts not only meet dimensional specs but also excel in their final environment, enhancing your product's value and reliability.