🔩 Roughness determinations - what is worth knowing in the context of metalworking?

In processes such as rolling, millingwhether grindingOne of the key parameters influencing the quality of steel components is surface roughness. Understanding the roughness symbols allows not only the correct design of the workpiece, but also the selection of the appropriate machining method - especially in the case of CNC machining and large-scale processing.

✅ Main roughness determinations

In technical documentation, we encounter several basic symbols for surface roughness. Here is their meaning:

1. Basic symbol (no additional markings)

Surface roughness

➡️ Means that the required roughness can be obtained by any method.
Such an area can be processed (e.g. by CNC milling) or left rawdepending on the quality of the starting material.

2. Roughness after machining

Surface roughness

➡️ This symbol indicates that the required roughness is to be achieved by removal of material - e.g. by means of rolling, sanding or CNC milling.
It is used in all mechanical components where metal or plastic parts work together.

3. Roughness without treatment (untreated surface)

Surface roughness

➡️ In this case the surface should meet the roughness requirements without any processing. Most often, this concerns surfaces that are hidden or invisible in the finished construction.

4. Machining around the entire surface (all-round symbol)

Surface roughness

➡️ Means that the required roughness applies to the full surface of the componentand not just a selected fragment.
The symbol is used on the drawing to avoid labelling each surface individually.

🛠️ Additional labelling - what is worth including?

Surface roughness

Supplementary information relevant to technology selection may also appear in the documentation:

  • a - roughness value (e.g. N10, Ra 3.2, Rz 100)
  • b - information on the suggested processing method (e.g. water jet, laser, milling)

It is these parameters that determine whether a surface is to be machined or not, if so by what method and with what accuracy. Whether it can be cut by laser, plasma or water jet, whether it must be machined by conventional or numerical control (CNC) turning or milling, and whether it requires precision grinding.

ISO 1302:2004 DIN 4768 PN-58/M-04252 PN-87/M-04251
GRADE Ra [µm] Rz [µm] GRADE Ra [µm] Rz [µm] GRADE Ra [µm] Rz [µm]
0,025 0,1÷0,8 0,04 0,2 0,04 0,16
0,05 0,25÷1,6 0,08 0,4 0,08 0,32
0,1 0,4÷2,5 0,16 0,8 0,16 0,63
0,2 0,8÷4 0,32 0,16 0,32 1,25
0,4 1,6÷6,3 0,63 3,2 0,63 2,5
0,8 3,15÷12,5 1,25 6,3 1,25 5
1,6 6,3÷20 2,5 10 2,5 10
3,2 12,5÷31,5 5 20 5 20
6,3 25÷63 10 40 10 40
12,5 40÷100 20 80 20 80
25 80÷160 40 160 40 160
50 160÷250 80 320 80 320
– – – – – – 160 630
– – – – – – 320 1250

🧠 Why is knowledge of roughness determinations important?

➡️ A well-chosen method for machining metals and plastics can reduce machining time, lowering production costs and, at the same time, ensuring the durability and functionality of the components made.


➡️ The higher the accuracy of the machined surfaces, the higher the production costs, as high machining accuracy is associated with longer machine and operator time.


➡️ The higher the machining accuracy, the longer the service life of the components working together, as high accuracy is associated with less friction during component operation.

Need support in metalworking, steel construction, CNC detail design, design of special tools or machines and equipment?
👉 Contact me - I can help you choose the right technology, ensure the quality of the workmanship and optimise the process.

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