Considerations For Surface Finishing In CNC Machining

In the complex world of CNC machining, the importance of surface finish cannot be described in words. It can play a crucial role in the quality, aesthetics, functionality, and overall cost of the final product.

This article explores the key points, objectives, and key factors to consider when determining the appropriate surface finish of CNC machined parts.

What Is Surface Finish?

Surface finish refers to the texture and smoothness of the external surface of the machined part. It is a key parameter that not only affects the appearance of the part, but also affects the mechanical and performance of the part.

By controlling surface finish, manufacturers can enhance corrosion resistance, reduce friction, improve sealing ability, and ensure that parts meet the specifications required for their intended applications.

Surface Finish VS Surface Finishing

Surface finish refers to the quality and characteristics of a material’s surface, such as texture, roughness, and appearance.

On the other hand, surface finishing refers to modifying the surface of a material to achieve the desired surface finish. Surface finishing can involve various techniques, such as polishing, sanding, sandblasting, coating, or painting, to improve the surface quality, functionality, or aesthetics of materials.

In short, surface finish refers to the quality, overall texture, and characteristics of the surface. In contrast, surface finishing refers to the process of modifying the surface to achieve the desired smoothness.

What Is The Purpose Of Surface Treatment?

1. Function:

The surface finish can directly affect the performance of the product. For example, if the surface of a bearing or shaft is too rough, it may lead to excessive wear and premature failure. On the other hand, if the surface is too smooth, it can lead to insufficient friction and reduce the product’s ability to function properly. Achieving the correct surface finish is crucial for ensuring that the product operates as expected and also helps to extend the service life of related tools.

2. Aesthetics:

The surface finish of a product can also affect its appearance, which is crucial for industries such as automobiles or consumer goods. High quality surface finish can make products look more attractive and enhance their perceived value.

3. Durability:

A fully polished surface also helps to protect the product from environmental factors such as corrosion, oxidation, or chemical erosion. For example, for metal parts, polished metal surfaces are more resistant to rust than rough, unpolished surfaces.

4. Manufacturing efficiency:

The required surface finish can also be achieved by reducing the need for additional processing steps such as polishing or grinding to help improve manufacturing processes and efficiency. This can save time and resources, and help simplify the production process.

5. Safety:

surface finish can also affect the safety of the product. For example, rough surfaces on manual tools may cause blisters or abrasions, while smooth surfaces on handrails may increase the risk of falls. Appropriate surface finish can help mitigate these risks and improve tool performance.

Machining Metal Parts

What Considerations Are Needed To Determine Surface Finish


Aesthetics plays a crucial role in the visual appeal of the final product. As a designer, it is important to decide where visible tool path lines are acceptable and where they are not. This is usually the difference between the customer-oriented and internal aspects of a component.


Although surface finish is usually related to aesthetics, it is important to recognize that it does play a role in functionality. such as

Friction And Wear Performance

A smoother surface finish can reduce friction between moving parts, thereby minimizing wear and extending the service life of the components. This is crucial for applications where components slide or rotate against each other.

Sealing And Fluid Flow

For components involving sealing applications, such as O-rings and washers, selecting the appropriate surface finish is crucial. Excessive roughness can create gaps, leading to liquid or gas leakage and damaging sealing integrity. A properly machined surface ensures tight and uniform contact between mating surfaces, promoting effective sealing, preventing leaks, and maintaining system integrity.

Adhesion And Adhesion

The surface finish will affect the bonding strength. For example, when using adhesives or connecting components through processes such as soft soldering or brazing, surface finish will directly affect the strength and reliability of the bonding. A rougher surface finish can produce a larger surface area, promoting stronger adhesion and longer lasting adhesion.


In electronic components, surface finish can affect conductivity. A rougher surface can hinder the smooth flow of electrons and may increase resistance. A smooth and clean surface finish ensures reliable electrical connections, reduces the risk of signal interference, and reduces the generation of heat.

Cost Impact

Overspecifying surface finish can have a significant impact on cost. As you may have guessed, higher specifications of smoothness will increase processing time.

In addition, it will accelerate tool wear, especially for harder materials such as stainless steel, and increase the possibility of requiring professional tools (which are therefore more expensive).

A higher surface finish will also have an impact on packaging requirements. Lower specifications of surface finish can allow components to be stacked for transportation, while higher specifications of surface finish may require separate packaging.

It is crucial to strike a cautious balance between cost and surface finish specifications. Not all surfaces need to be the same, so please consider relaxing the surface finish on non critical or hidden surfaces.

Quality control/inspection requirements

Realizing high tolerance surface finish is of great significance for quality control and inspection processes. The process and final inspection have become more time-consuming and complex, increasing overall costs.

In addition to visual inspection, high specification surface finish may require additional 100% non-contact inspection, or additional inspection by using a microscope, coordinate measuring machine (CMM), shadow map, surface tester, or feeler gauge. Therefore, please ensure that your budget meets the required level of quality control.

What needs to be considered in order to achieve the desired surface finish?

1. Material selection

The selected material type not only affects the simplicity and cost-effectiveness of processing, but also determines the achievable surface finish tolerance. For example, aluminum typically produces smooth results, while stainless steel requires more time and advanced technology and tools to achieve similar surface finishes.

In addition, the selected material will affect the cutting tools used in the machining process, thereby affecting the final surface finish and cost.

The specific material grade is another key factor, as it can significantly affect the appearance after processing, especially after applying precision machining techniques.

To ensure a seamless process, it is necessary to create a prototype using the materials and grades you have selected, including the specified surface finish and any finishing process. This will enable you to identify potential issues or areas for improvement.

2. Tool selection

Appropriate tools are crucial for achieving the required surface finish during the manufacturing process. For example, hard alloy and diamond coated tools are commonly used to achieve a smooth surface finish.

3. Processing parameters

The machining parameters such as spindle speed, feed rate, cutting depth, and cutting fluid all play a role in achieving the correct surface finish. The appropriate combination of these parameters depends on the material being processed and the required surface finish.

4. Surface treatment

Preparing the material surface before processing is crucial for ensuring a smooth machining surface finish. This may involve cleaning materials, using lubricants or coolants during the machining process, or applying surface coatings or treatments to protect the machined surface from damage.

5. Skills and experience of operators

Skilled operators who understand the processing materials and appropriate processing parameters can optimize the processing technology to achieve the desired surface finish.


CNC surface finishing is a complex field that requires attention to details from surface preparation to final application. Understanding common problems and how to prevent them can ensure high-quality results that meet or exceed expectations.

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