Surface Roughness Chart
The Ra finish each production method leaves on steel, from flame cutting and sawing down to lapping and superfinishing. Every row shows the range that is routinely produced and the wider range that can still occur, in micrometers and microinches, with the roughness grade numbers and the cut-off values that go with them.
Roughness ranges by production method, redrawn from the source chart. Left to right runs from rough to smooth.
| Processo | Average application, Ra | Less frequent application, Ra |
|---|---|---|
| Flame Cutting | 25 to 12.5 µm 1000 to 500 µin | 50 to 6.3 µm 2000 to 250 µin |
| Snagging | 25 to 6.3 µm 1000 to 250 µin | 50 to 3.2 µm 2000 to 125 µin |
| Sawing | 25 to 1.6 µm 1000 to 63 µin | 50 to 0.80 µm 2000 to 32 µin |
| Planing, Shaping | 12.5 to 1.6 µm 500 to 63 µin | 25 to 0.40 µm 1000 to 16 µin |
| Perfuração | 6.3 to 1.6 µm 250 to 63 µin | 12.5 to 0.80 µm 500 to 32 µin |
| Chemical Milling | 6.3 to 1.6 µm 250 to 63 µin | 12.5 to 0.80 µm 500 to 32 µin |
| Elect. Discharge Mach. | 4.5 to 1.6 µm 180 to 63 µin | 12.5 to 0.80 µm 500 to 32 µin |
| Fresagem | 6.3 to 0.80 µm 250 to 32 µin | 25 to 0.141 µm 1000 to 5.66 µin |
| Broaching | 3.2 to 0.80 µm 125 to 32 µin | 6.3 to 0.40 µm 250 to 16 µin |
| Alargamento | 3.2 to 0.80 µm 125 to 32 µin | 6.3 to 0.40 µm 250 to 16 µin |
| Electron Beam | 6.3 to 0.80 µm 250 to 32 µin | 6.3 to 0.20 µm 250 to 8 µin |
| Laser | 6.3 to 0.80 µm 250 to 32 µin | 6.3 to 0.20 µm 250 to 8 µin |
| Electro-Chemical | 3.2 to 0.20 µm 125 to 8 µin | 12.5 to 0.05 µm 500 to 2 µin |
| Boring, Turning | 6.3 to 0.40 µm 250 to 16 µin | 25 to 0.025 µm 1000 to 1 µin |
| Barrel Finishing | 0.80 to 0.20 µm 32 to 8 µin | 3.2 to 0.05 µm 125 to 2 µin |
| Electrolytic Grinding | 0.566 to 0.20 µm 22.6 to 8 µin | 0.80 to 0.10 µm 32 to 4 µin |
| Roller Burnishing | 0.40 to 0.20 µm 16 to 8 µin | 0.80 to 0.10 µm 32 to 4 µin |
| Moagem | 1.6 to 0.10 µm 63 to 4 µin | 6.3 to 0.025 µm 250 to 1 µin |
| Honing | 0.80 to 0.10 µm 32 to 4 µin | 1.6 to 0.025 µm 63 to 1 µin |
| Electro-Polish | 0.80 to 0.10 µm 32 to 4 µin | 1.6 to 0.012 µm 63 to 0.5 µin |
| Polimento | 0.40 to 0.10 µm 16 to 4 µin | 0.80 to 0.012 µm 32 to 0.5 µin |
| Lapping | 0.40 to 0.05 µm 16 to 2 µin | 0.80 to 0.012 µm 32 to 0.5 µin |
| Superfinishing | 0.20 to 0.025 µm 8 to 1 µin | 0.80 to 0.012 µm 32 to 0.5 µin |
| Sand Casting | 25 to 12.5 µm 1000 to 500 µin | 50 to 6.3 µm 2000 to 250 µin |
| Hot Rolling | 25 to 12.5 µm 1000 to 500 µin | 50 to 6.3 µm 2000 to 250 µin |
| Forjamento | 12.5 to 3.2 µm 500 to 125 µin | 25 to 1.6 µm 1000 to 63 µin |
| Perm. Mold Casting | 3.2 to 1.6 µm 125 to 63 µin | 6.3 to 0.80 µm 250 to 32 µin |
| Investment Casting | 3.2 to 1.6 µm 125 to 63 µin | 6.3 to 0.40 µm 250 to 16 µin |
| Extruding | 3.2 to 0.80 µm 125 to 32 µin | 12.5 to 0.40 µm 500 to 16 µin |
| Cold Rolling, Drawing | 3.2 to 0.80 µm 125 to 32 µin | 6.3 to 0.20 µm 250 to 8 µin |
| Fundição sob pressão | 1.6 to 0.80 µm 63 to 32 µin | 3.2 to 0.40 µm 125 to 16 µin |
| Grau | Ra, µm | Ra, µin |
|---|---|---|
| N12 | 50 | 2000 |
| N11 | 25 | 1000 |
| N10 | 12.5 | 500 |
| N9 | 6.3 | 250 |
| N8 | 3.2 | 125 |
| N7 | 1.6 | 63 |
| N6 | 0.80 | 32 |
| N5 | 0.40 | 16 |
| N4 | 0.20 | 8 |
| N3 | 0.10 | 4 |
| N2 | 0.05 | 2 |
| N1 | 0.025 | 1 |
| Preferred series of Ra values, µm (top) and µin (bottom) | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| 0.012 0.5 | 0.025 (um) 1 | 0.050 (um) 2 | 0.075 3 | 0.10 (um) 4 | 0.125 5 | 0.15 6 | 0.20 (um) 8 | 0.25 10 | 0.32 13 |
| 0.40 (um) 16 | 0.50 20 | 0.63 25 | 0.80 (um) 32 | 1.00 40 | 1.25 50 | 1.60 (um) 63 | 2.0 80 | 2.5 100 | 3.2 (um) 125 |
| 4.0 160 | 5.0 200 | 6.3 (um) 250 | 8.0 320 | 10.0 400 | 12.5 (um) 500 | 15 600 | 20 800 | 25 (um) 1000 |
(a) Recommended values.
| Cutoff, mm | Cutoff, in. |
|---|---|
| 0.08 | 0.003 |
| 0.25 | 0.010 |
| 0.80 | 0.030 |
| 2.5 | 0.1 |
| 8.0 | 0.3 |
| 25.0 | 1.0 |
- Ra is quoted in micrometres and microinches throughout, the two rows of the source chart.
- A surface machined by one process is often improved by a finishing process later in the chain, turned and then ground and then honed. Read the chart left to right for the processes that follow.
- The ranges are general shop values. The finish a cut actually leaves depends on the material, the tool or wheel, the rigidity of the setup and the feed used.
Reading the chart
The process rows run from the roughest finishes at the top to the smoothest at the bottom, and the scale runs from Ra 50 µm at the left down to 0.012 µm at the right. A grey bar that extends past a value means the process can reach that roughness under favourable conditions, and the dark section is where the process usually sits. When a drawing calls for a finish, check that the process named for the last operation on the part can hold it. A milled surface is usually quoted at Ra 3.2 to 0.80 µm, which is why grinding or lapping follows where the drawing is tighter than that.
How fast the steel can be machined, and with which tool, is covered in the gráfico de classificação de usinabilidade e no cutting speeds and feeds for tool steels. Surface treatments that add a layer rather than cut one are a different subject, on the surface treatment page.
Páginas de referência relacionadas
Machining allowance chart · Tabela de propriedades do aço ferramenta
Source: Machinery’s Handbook 28th Edition (Industrial Press), Surface Texture section: Table 1 (roughness produced by common production methods), Table 2 (standard cutoff values), Table 3 (preferred series of Ra values), Table 4 (roughness grades). The chart is redrawn from the source. Values are converted between micrometres and microinches at 1 µm = 39.37 µin (0.0254 µm = 1 µin).