Choosing the Right Surface Finish for CNC Machining

A CNC machined part isn’t done once the CNC machining process stops running.

Finishing is the final step in the manufacturing process (outside of assembly) and involves various techniques to improve your parts’ appearance, functionality, and durability. The finishing process is crucial to achieving the desired properties of your machined parts.

This article explores some of the most popular finishes for CNC machining, from sandblasting to painting and everything in between. 

What is Surface Finish?

Surface finish refers to the texture and smoothness of a machined part’s exterior.

It is a critical parameter that affects not only the appearance but also the mechanical properties and performance of the part. By controlling the surface finish, manufacturers can enhance corrosion resistance, reduce friction, improve sealing capabilities, and ensure the part meets the specifications for its intended application.

A well-chosen surface finish can significantly extend the lifespan of a part and improve its overall functionality.

Factors to Consider When Choosing a CNC Machining Surface Finish

Choosing the right surface finish for CNC machined parts is crucial to ensure that the part meets the desired functional and aesthetic requirements. Some of the key factors to consider when selecting a CNC machining surface finish include:

• Functionality: The surface finish should be selected based on the part’s functional requirements. For example, parts that require high wear resistance or corrosion resistance may require a stronger surface finish, such as anodizing or electroplating.

• Material: Certain CNC surface finishes are more suitable to specific CNC materials than others. For example, anodizing is typically usable on aluminum parts, while electroplating is ideal for conductive metal parts.

• Aesthetics: The surface finish should be selected based on the part’s desired appearance. Different surface finishes, such as high gloss or matte finishes, can produce a range of visual effects.

• Cost: Some finishes may be more expensive than others. For instance, powder coating will be much more costly than regular paint. So, balancing all parameters, including costs, function, and time, is essential to getting the optimum surface finish.

• Lead time: Different finishing methods require varying amounts of time to complete. For example, if you need a product quickly, you may need to choose a quicker method, such as polishing.

• Environmental impact: The environmental impact of the surface finish process must be considered, and eco-friendly options must be explored whenever possible.

• Part geometry: The part’s geometry can also affect the choice of surface finish. For example, tight tolerances may require a different finish than parts with a more forgiving design.

Hardening

Metal is heated to a high temperature during hardening and then quickly cooled.

This process changes the part’s mechanical properties, making it stronger and more wear-resistant. Hardening is commonly used for parts that will undergo heavy usage or wear. There are several types of hardening, including case hardening, through hardening, and induction hardening. Case hardening is the most common.

When to use hardening: Hardening is ideal for parts that need to withstand high stress or wear, such as gears, bearings, and cutting tools.

Tempering

Tempering is similar to heating in that it involves heating a metal to a specific temperature. The difference is that the part is cooled slowly rather than quickly.

This process improves the metal’s toughness and ductility, making it less brittle and more able to withstand deformation.

When to use tempering: Tempering is best used for parts that need to maintain their strength while also being able to bend or deform slightly, such as springs and shafts.

Anodizing

The anodizing process involves creating a protective oxide layer on the surface of a metal. The part is immersed in an electrolytic solution, and a current passes through it.

Anodizing creates a hard, durable, and corrosion-resistant surface. Afterward, the part can also be easily dyed in various colors.

When to use anodizing: This finish is commonly used for parts that need to resist corrosion and wear, such as medical equipment and aerospace components.

Painting

As you probably know, painting is a process that involves applying a coating of paint to a surface.

This coating adds a desired color and provides some surface protection. Paints can be formulated to resist corrosion, abrasion, and other environmental factors.

When to paint: Painting is ideal for parts that need to be aesthetically pleasing or require protection against the elements (such as parts that will be outdoors)

Black Oxidizing

Black oxidizing adds a black finish to the surface of a metal.

The metal is immersed in an oxidizing solution, which creates a thin layer of black oxide on the surface. This finish improves the part’s wear resistance and looks visually appealing.

When to use black oxidizing: Black oxidizing is commonly used for parts that need to be visually appealing or wear-resistant.

Sandblasting

Abrasive particles are propelled at the part’s surface during the sandblasting process.

This process can create a matte finish, improve grip, or remove unwanted material from a part’s surface for a smoother surface.

When to use sandblasting: Sandblasting is ideal for parts that need a specific texture or grip.

Sourcing Your CNC Machined Parts 

Choosing the right finishing option for your CNC machined parts is essential to achieve the desired properties and functionality.

Each finishing option has unique advantages and is suitable for different applications. Whether you need to improve a part’s wear resistance, make it corrosion-resistant, or improve its appearance, a finishing option can help.

The MakerVerse platform can also help. We offer a one-stop shop where you can source parts from the full range of manufacturing technologies – including CNC machining – with the necessary finishes.