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CNC machining parts :Comparison of Surface Roughness Measurement Methods

CNC Milling Machines : Various Types Of Analysis

In the realm of precision engineering, surface roughness holds paramount importance. It serves as a tangible indicator of the quality and precision of CNC machining parts. As manufacturers aim for higher standards of performance and aesthetics, the ability to judge surface roughness accurately becomes increasingly critical.

What is Surface Roughness

The machined surface has small spacing and small peak-to-valley unevenness. The distance (wave pitch) between the two wave crests or two wave troughs is very small (below 1mm), which belongs to the micro-geometric error.

CNC machining parts : Surface Roughness Forming Factors

Surface roughness is generally formed by the processing method employed and other factors. For example, the friction between the tool and the part’s surface during the machining process, the plastic deformation of the metal on the surface layer when the chips are separated, the high-frequency vibration in the processing system, and the discharge pits electrical machining. Due to different processing methods and workpiece materials, the depth, density, shape, and texture of marks left on the machined surface are different.

4 major criteria to Verifying CNC Machined Parts Quality
CNC machining

Surface roughness directly influences the functionality, performance, and appearance of machined parts. In functional applications such as aerospace or automotive industries, precise surface finishes are imperative to ensure optimal performance and durability.

Several factors influence the surface roughness of CNC machined parts, including machining parameters, tool geometry, material properties, and machine dynamics. Optimizing these factors is crucial for achieving the desired surface finish and ensuring consistency across multiple parts. For instance, adjusting cutting speed, feed rate, and depth of cut can help mitigate tool vibrations and enhance surface quality.

CNC machining parts : Comparison of Surface Roughness Measurement Methods

Various methods exist for quantifying surface roughness, with each offering unique insights into different aspects of the surface texture. The most commonly used method is the measurement of Ra (average roughness) using profilometers or surface roughness testers. This method provides a numerical value representing the average deviation of surface peaks and valleys from the mean line over a specified sampling length.

ProfilometryContact measurement with a stylusHigh accuracy, suitable for a wide range of surfacesLimited to 2D measurements, can damage delicate surfaces
Optical MethodsLight reflection/refraction for measurementNon-contact, suitable for delicate or sensitive surfacesLimited accuracy on highly reflective or transparent surfaces
Atomic Force Microscopy (AFM)Atomic-level scanning probe microscopyExtremely high resolution, suitable for nanoscale featuresTime-consuming, limited area coverage
Roughness Comparison ScalesVisual/ tactile comparison with standard samplesSimple and intuitive, no specialized equipment requiredSubjective, limited accuracy

List of Best Practices for Surface Roughness Control

CNC Machining
  1. Optimize machining parameters based on material properties and desired surface finish.
  2. Use high-quality cutting tools with appropriate geometries and coatings.
  3. Minimize tool deflection and vibration by selecting suitable tool paths and cutting strategies.
  4. Implement effective chip evacuation mechanisms to prevent re-cutting and surface contamination.
  5. Regularly maintain CNC machines to ensure stable performance and accuracy.

CNC machining parts :Applications of Surface Roughness Standards

Surface roughness standards such as ISO 1302 and ASME B46.1 provide guidelines for specifying and evaluating surface finishes in various industries. These standards define parameters such as roughness cutoff length, sampling length, and measurement conditions, facilitating consistent and objective assessment of surface quality. Compliance with these standards ensures interoperability and interchangeability of machined parts in global supply chains.


In conclusion, the ability to judge surface roughness accurately is indispensable for ensuring the quality, functionality, and aesthetics of CNC machining parts. By understanding the various measurement methods, challenges, and influencing factors, manufacturers can implement effective strategies for surface roughness control. Adherence to industry standards further enhances the reliability and consistency of surface finish evaluations, contributing to overall product excellence and customer satisfaction.