Surface Roughness of Machining Processes
Engineering reference for surface roughness values including Ra, Rz, Rt, and typical machining process finishes
Typical Machining Surface Roughness Table
| Process / Finish | Ra (µm) | Rz (µm) | Rt (µm) | Notes |
|---|---|---|---|---|
| Turning (fine) | 0.8 | 6.3 | 7.9 | Single-point cutting tool, light feed |
| Turning (medium) | 1.6 | 12.5 | 15.8 | Standard lathe finish |
| Milling (fine) | 1.6 | 12.5 | 15.8 | Face milling or end milling, fine cutter |
| Milling (medium) | 3.2 | 25.0 | 31.5 | Standard rough milling |
| Grinding | 0.4 | 3.2 | 4.0 | Surface grinder, precision finish |
| Polishing | 0.1 | 0.8 | 1.0 | High gloss, mirror finish |
| Lapping | 0.05 | 0.4 | 0.5 | Ultra-precision finishing |
| Sandblasting | 3.2-6.3 | 25-50 | 31-63 | Textured surface, decorative or functional |
| Shot Peening | 1.6-3.2 | 12.5-25 | 15.8-31.5 | Improves fatigue resistance |
Typical Surface Roughness of Machining Processes Chart
About Surface Roughness in Engineering and Manufacturing
Surface roughness is one of the most critical parameters in mechanical design, machining, and manufacturing. It directly influences friction, lubrication, wear resistance, fatigue life, sealing performance, and aesthetics of engineered components. Selecting the correct surface finish ensures parts meet their functional, performance, and dimensional requirements.
This surface roughness reference chart presents typical values for Ra (Arithmetic Average Roughness), Rz (Mean Peak-to-Valley Height), and Rt (Total Profile Height) across common machining and finishing processes such as turning, milling, grinding, polishing, lapping, sandblasting, and shot peening. Engineers and machinists can use this chart to quickly identify appropriate finishes, compare process capabilities, and specify surface requirements in engineering drawings.
Key Surface Roughness Parameters
- Ra – Arithmetic Average Roughness The average vertical deviation of surface irregularities from the mean line. Widely used as the standard measure of surface finish for general engineering applications.
- Rz – Mean Peak-to-Valley Height The average height between the five highest peaks and five deepest valleys across a sampling length. Critical for assessing functional and precision surfaces where surface texture affects contact performance.
- Rt – Total Height of Profile The maximum distance between the highest peak and lowest valley within the sampling length. Used to evaluate maximum surface deviation and detect machining defects.
Importance of Surface Finish in Engineering Applications
Accurate control of surface texture is essential for achieving:
- Reduced friction and improved wear resistance in moving components.
- Better lubrication retention and lower operating temperatures in assemblies.
- Proper sealing and fit for fluid systems and mating surfaces.
- Enhanced fatigue performance and material longevity under cyclic loads.
- Improved aesthetics and corrosion resistance for visible or exposed components.
Using the Surface Roughness Chart
This chart helps engineers and manufacturers:
- Select the optimal machining or finishing process to achieve the required Ra, Rz, or Rt value.
- Define surface texture symbols and tolerances on technical drawings according to ISO or ASME standards.
- Ensure quality control and process verification during production and inspection stages.
- Balance surface finish requirements with cost, machining time, and tool wear considerations.
Whether designing precision bearings, gears, sealing faces, or molded parts, understanding and specifying the correct surface roughness ensures optimal performance and product reliability. The Surface Roughness Reference Chart serves as a reliable guide for mechanical engineers, CNC machinists, quality inspectors, and manufacturing professionals seeking accuracy, consistency, and compliance in surface finish specification.