CNC Machining Surface Finish

Have you ever wondered what the different CNC machining surface finishes available are and what they do? CNC machining is a rapidly growing field that allows for the creation of intricate and high-quality objects using a machine. But what is the surface finish of a CNC machined part? And how do you achieve it? In this blog post, I will answer these questions and provide tips on how to achieve the perfect surface finish for your CNC machined parts. I will also discuss the different types of finishes available and how to choose the correct one for your needs. So whether you need clarification on the surface finish of your CNC machined parts or want to get started, this blog post is for you.

Importance of CNC Machining Surface Finish In CNC Machined Part

CNC machining uses a machine tool to produce parts by cutting, grinding, or other methods. It allows for the creation of intricate, high-quality components that are often used in industrial and consumer products. The CNC machining surface finish of these components is an important part of the manufacturing process as it can directly impact their performance and overall appearance. In CNC machining, the cnc surface finish is usually determined by he type of tooling used and the accuracy with which it cuts the component. With proper tooling and good-quality materials, high-quality surface finishes can be achieved, resulting in high-quality components with improved performance. There are various types of CNC machining, including 3D printing, milling, and turning. Each has its own features and benefits that can be used to produce high-quality components with improved performance.

Surface Finishes for CNC Machining and Manufacturing: Choose the Best One

The surface finishes used on CNC machined parts can significantly impact the overall appearance, surface roughness, and quality of your final product. Choose the best finish from many finishing options available can be a challenge, especially for novice machinists and woodworkers, as there are many different options available. Here, I will explore some of the most common useful CNC machining surface finishes and provide tips on how to choose the best one for your project or prototype, or any other aluminum parts. So, let’s go on.


Passivation is a process in which a surface finish is applied to a material to protect it from the elements and prevent corrosion. Different types of passivation can be applied depending on the material and application requirements. These include chemical passivation, electrochemical passivation, and physical passivation. Chemical passivation can be performed using acids, bases, or alkalis that are dissolved in solvents such as water or alcohol. These solvents can also contain surfactants or emulsifiers that help reduce surface tension and increase the lubricity of the surface of metal. Electrochemical passivation involves passing an electric current through a solution containing an electrolyte that dissolves metal ions in the solution. The metals deposited on the surface are typically less reactive than their parent compounds, which allows them to be used in more advanced applications where rapid oxidation of other components is desired. Physical passivation involves applying one or more layers of a solid or liquid agent directly to the surface of a material.

cnc machining surface finish(passivation)

Passivation process can be used to create a protective layer on materials such as steel that are susceptible to corrosion. Passivation can be performed using different types of finishes depending on the application requirements and material properties. Here are some types of passivation you may consider for use:

Oxidation: In this process, an oxidizing agent such as nitric acid or oxygen is added to a solution containing metals dissolved in an organic solvent such as acetone or ethanol. This causes oxide compounds to form on the surface of a part resulting in a dulled appearance and increased corrosion resistance.

Alkaline: In this process, an alkaline solution containing hydroxides or carbonates is added to a solution containing metals dissolved in an organic solvent. This causes the metal ions to form insoluble salts that coat the surface of the material and protect it from corrosion.

Acid: In this process, an acid such as hydrochloric or sulfuric acid is added to a solution containing metals dissolved in an organic solvent. This causes metal ions to dissociate and form free electrons that are captured by the acids, leading to passivation and increased corrosion resistance.

Bead Blasting

Bead blasting is a surface finishing process that uses beads or marbles to get the ideal surface of a material by abrading away small amounts of material. This process is commonly applied to metals, plastics, and other hard materials to give them a smooth, glossy appearance. You can also use bead blasting to remove product’s surface imperfections and to increase surface quality such as scratches and dents in metal parts. It is an effective way to prepare surfaces for coating or finishing processes. Bead blasting is often used in CNC machining to clean the surface of hard materials (such as aluminum) before they are cut into pieces. Removing small amounts of material with bead blasting makes it easier for the machinist to form the desired shape in the material by grinding, cutting, or drilling it.

Advantages: Bead blasting is the ability to remove surface imperfections and prepare materials for coating or finishing processes without affecting their underlying properties. Bead blasting is often used in CNC machining because it is an efficient way to clean the surface of hard materials before they are cut into pieces. It can be done at any stage in the manufacturing process, from the initial roughing out of a part to the final finishing method and assembly. 

Disadvantages: Bead blasting includes the cost involved in purchasing and maintaining equipment for the process and the possibility of damaging certain materials with excessive bead blasting. 


As-machined surface finishes are used in CNC machining to provide a smooth, clean finish on parts. These finishes are applied after machining to give the final product a smooth, polished look. Similar to paint, as-machined surface finishes are applied by hand and can be applied to various materials including metals, wood, and plastics. The finishing process can vary depending on the type of material being processed.

  • With metals, as-machined surface finishes may include oiling or waxing to protect the surface from wear and tear.
  • With wood, as-machined surface finishes may include varnishes or lacquers to protect the surface from moisture and wear.
  • With plastics, as-machined surface finishes may include adhesives or sealants to bond the part together.

Aside from their function in providing a smooth finish for parts, as-machined surface finishes are also used in various industrial applications such as paints for machinery and floors. They offer high durability and resistance to wear and tear due to their special formulation. They have excellent adhesion properties making them suitable for bonding purposes. 

As-machined surface finishes are also used in construction industries where they are used for sealing joints between tiles and walls or between wooden boards and masonry surfaces. They can provide long-term protection against moisture and abrasion while allowing easy maintenance and cleaning of surfaces. 

Anodizing(Type II and III)

Anodizing is one of the surface finishing options that is used to enhance the characteristics of a material by electro-depositing an oxide or mixture of oxides onto its surface. It has several applications in the manufacturing industry, including CNC machining. Anodizing allows for increased durability and wear resistance, as well as increased abrasion and corrosion resistance. It is also used in various surface-tensioned compounds, such as paints, coatings, and adhesives, to provide high adhesion and cohesion. Anodizing can be performed in two different types: Type II anodizing and Type III anodizing. Type II anodizing uses a milder form of the electrochemical process while Type III anodizing uses a harsher form of the process.

Type II: This type of anodizing involves applying a solution containing nickel ions at a low voltage to the surface to be anodized. The solution is then allowed to dwell on the surface for a predetermined period of time before being removed. In this type of anodization, the nickel ions are deposited on the surface via oxidation reactions with the electrons in the solution. This results in a surface with a striped pattern due to the formation of metal oxides (e.g., nickel oxide). The concentration of nickel ions must be carefully controlled to form a uniform layer but not too thick for optimal adhesion and corrosion resistance.

Type III: This anodizing process involves applying a higher voltage than Type II anodization and allowing it to dwell on the surface longer before being removed (i.e., longer exposure time). This type of anodization uses more intense electrolysis processes resulting in thicker layers with greater concentrations of nickel compounds on the surface. Type III anodizing is typically used for more ornate surfaces and can be more difficult to achieve the desired result due to the greater potential for contamination.

What do You Have in Consideration for CNC machining surface finish?

You should consider some issues when selecting the surface finish for a CNC machined part including the desired quality, material choice, machine settings, and cost.

  • Quality refers to the level of smoothness and precision of the finished product. Different types of machines and materials can produce different levels of quality, but generally speaking, higher-end machines are more likely to produce high-quality surfaces.
  • Material choice is another important factor to consider when choosing a CNC machined surface finish. Different materials have different properties and characteristics that can affect the final result, such as hardness, wear resistance, and heat tolerance.
  • In the same way, machine settings can also affect the quality of the finished product. Certain types of machines may be more suited for certain types of materials and may produce better results with those materials. 
  • Cost can also influence your decision on the type of surface finish for your metal machined parts and parts made from aluminum as well. With all these factors in mind, you can select a suitable CNC-machined surface finish that will meet your requirements and budget.


CNC machining surface finish is an important part of the final product, and it can make a big difference in how your CNC machine performs. Throughout the article, I have discussed surface finish, how it affects CNC machining, and some types of surface finish available. I have also provided tips on how to achieve the desired surface finish, and discuss some of the benefits that can be achieved with a properly finished CNC machining surface. Hope you have enjoyed it and this will help you to complete your cnc project more precisely.