Surface Roughness In CNC Machined Parts

DALIAN, China - Aug. 31, 2025 - PRLog -- What Is Surface Roughness?

Surface roughness refers to the small, finely spaced deviations from the nominal surface geometry that occur as a result of machining processes. These microscopic peaks and valleys are often imperceptible to the eye but are critical for technical applications.

It is typically expressed in micrometers (µm) or microinches (µin), and common units include:

Ra (Roughness Average) – the arithmetic average of absolute values of surface height deviations.

Rz (Mean Roughness Depth) – the average distance between the highest peak and the lowest valley in a sample area.

Rt (Total Height of the Roughness Profile) – the vertical distance between the highest peak and the lowest valley in a single assessment length.

Why Surface Roughness Matters

1. Functionality and Fit

The smoother the surface, the more precisely two parts can fit together. In applications such as fluid sealing, bearing assemblies, or tight-tolerance mechanical components, excessive surface roughness can lead to leakage, misalignment, or mechanical interference.

1. Wear and Friction

A rough surface tends to create more friction and can cause rapid wear on both the machined part and its mating surface. In contrast, smoother surfaces reduce contact resistance and extend component lifespan.

1. Coating and Finishing

Surfaces that are too rough may not hold coatings uniformly or might require additional finishing steps such as polishing, lapping, or anodizing. In critical parts, poor surface texture may also trap contaminants.

1. Stress Concentration

Microscopic valleys and notches on a rough surface can act as stress concentrators, reducing fatigue resistance. For components subjected to cyclic loads, surface roughness must be tightly controlled.

Factors affecting surface roughness in CNC machining

The final surface roughness is determined by the following factors:

Material properties: Compared to harder metals such as titanium, softer materials such as aluminum may require different processing strategies.

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