Surface Roughness Review
Surface roughness also known as surface profile Ra is a measurement of surface finish it is topography at a scale that might be considered "texture" on the surface. Surface roughness is a quantitative calculation of the relative roughness of a linear profile or area, expressed as a single numeric parameter (Ra).
The ability of a manufacturing operation to produce a specific surface roughness depends on many factors. For example, in end mill cutting, the final surface depends on the rotational speed of the end mill cutter, the velocity of the traverse, the rate of feed, the amount and type of lubrication at the point of cutting, and the mechanical properties of the piece being machined. A small change in any of the above factors can have a significant effect on the surface produced.
Surface Roughness Average Obtainable By Common Production Methods
Process |
Roughness Height Rating Microinches
2000 1000 500 250 125 63 32 16 8 4 2 1 0.5 |
Flame Cutting |
---------XXXX---------- |
Sawing |
------------XXXXXXXXXX--------- |
Drilling |
---------XXXXXXXXXXXXXX------------ |
EDM |
----------XXXXXXX-------- |
Milling |
-----------------XXXXXXXXXXXXX----------- |
Broaching |
-------XXXXXXXX-------- |
Reaming |
-------XXXXXXXX-------- |
Laser |
XXXXXXXXXXXXXX---------- |
Burnishing |
---------XXXXXXX------- |
Grinding |
--------------XXXXXXXXXXXXXXXXX-------- |
Honing |
-------XXXXXXXXXXXXX-------- |
Polishing |
-------XXXXXXXX------------------- |
Extruding |
-------------XXXXXXX------ |
Investment Casting |
------XXXX------------------ |
Perm Mold Cast |
------XXXX------------------ |
Die Casting |
------XXXXXX------ |
Ra = Roughness, average in micro-meters & micro-inches
| China's old standard (finish) |
China New standard (roughness) Ra |
American Standard(microns), Ra |
American Standard (Micro-inch), Ra |
| ▽ 4 |
6.3 |
8.00 |
320 |
| 6.30 |
250 |
| ▽ 5 |
3.2 |
5.00 |
200 |
| 4.00 |
160 |
| 3.20 |
125 |
| ▽ 6 |
1.6 |
2.50 |
100 |
| 2.00 |
80 |
| 1.60 |
63 |
| ▽ 7 |
0.8 |
1.25 |
50 |
| 1.00 |
40 |
| 0.80 |
32 |
| ▽ 8 |
0.4 |
0.63 |
25 |
| 0.50 |
20 |
| 0.40 |
16 |
| China Old Grade |
China New
Ra |
China New
Rz |
USA micron
Ra |
USA microinch
Ra |
| ▽ 1 |
50 |
200 |
|
|
| ▽ 2 |
25 |
100 |
|
|
| ▽ 3 |
12.5 |
50 |
|
|
| ▽ 4 |
6.3 |
25 |
8.00 |
320 |
| 6.30 |
250 |
| ▽ 5 |
3.2 |
12.5 |
5.00 |
200 |
| 4.00 |
160 |
| 3.20 |
125 |
| ▽ 6 |
1.6 |
6.3 |
2.50 |
100 |
| 2.00 |
80 |
| 1.60 |
63 |
| ▽ 7 |
0.8 |
6.3 |
1.25 |
50 |
| 1.00 |
40 |
| 0.80 |
32 |
| ▽ 8 |
0.4 |
3.2 |
0.63 |
25 |
| 0.50 |
20 |
| 0.40 |
16 |
| ▽ 9 |
0.2 |
1.6 |
0.20 |
12.5 |
| 10 |
| 8 |
| ▽ 10 |
0.1 |
0.8 |
0.10 |
|
| RMS (microinch) |
RMS
(µm) |
Ra (microinch) |
Ra
(µm) |
Grit Size |
80 58
47
34
17
14 |
2.03 1.47
1.2
0.6
0.43
0.36 |
71 52
42
30
15
12 |
1.32-1.90
0.46-0.64
0.3-0.4
0.18-0.38
≤0.15
≤0.08 |
80 120
150
180
240
320
400 |
Machining surface finish chart: Ra vs RMS
| USA Ra(µm) |
USA Ra (Micro inch) |
USA RMS (Micro inch) |
Machining Finish Method |
| 50.0 |
2000 |
2200 |
The most coarse machining or good rough casting surfaces |
| 25.0 |
1000 |
1100 |
Machining marks very obvious. Rough turning, boring, planning, drilling |
| 12.5 |
500 |
550 |
Machining marks obvious. Normal turning, boring, planning, drilling, grinding |
| 8.00 |
320 |
352 |
Machining marks visible. Normal turning, boring, planning, drilling , grinding |
| 6.30 |
250 |
275 |
Machining marks visible. Normal turning, boring, planning, drilling , grinding |
| 5.00 |
200 |
220 |
Machining marks not obvious. But still visible. Normal turning, boring, planning, drilling, grinding. |
| 4.00 |
160 |
176 |
Machining marks not obvious. But still visible. Normal turning, boring, planning, drilling, grinding. |
| 3.20 |
125 |
137.5 |
Machining marks not obvious. But still visible. Normal turning, boring, planning, drilling, grinding. |
| 2.50 |
100 |
110 |
Machining marks blur, but direction obvious. Number controlled turning, boring, planning, drilling, grinding. |
| 2.00 |
80 |
88 |
Machining marks blur, but direction obvious. Number controlled turning, boring, planning, drilling, grinding. |
| 1.60 |
63 |
69.3 |
Machining marks blur, but direction obvious. Number controlled turning, boring, planning, drilling, grinding. |
| 1.25 |
50 |
55 |
Machining marks direction blur, but still visible. Number controlled turning, boring, planing, drilling, grinding. |
| 1.00 |
40 |
44 |
Machining marks direction blur, but still visible. Number controlled turning, boring, planing, drilling, grinding. |
| 0.80 |
32 |
35.2 |
Machining marks direction blur, but still visible. Number controlled turning, boring, planing, drilling, grinding. |
| 0.63 |
25 |
27.5 |
Machining marks direction blur. Reaming, grinding, boring, rolling. |
| 0.50 |
20 |
22 |
Machining marks direction blur. Reaming, grinding, boring, rolling. |
| 0.40 |
16 |
17.6 |
Machining marks direction blur. Reaming, grinding, boring, rolling. |
| 0.20 |
12.5 |
13.75 |
Machining marks direction invisible. Grinding, super machining |
| 0.20 |
10 |
11 |
Machining marks direction invisible. Grinding, super machining |
| 0.20 |
8 |
8.8 |
Machining marks direction invisible. Grinding, super machining |
| 0.10 |
4 |
4.4 |
Surface dark gloss. Surper machining |
Ra is the arithmetic average of surface heights measured across a surface. Simply average the height across the microscopic peaks and valleys.
Ra and RMS are both representations of surface roughness, but each is calculated differently.
Ra is calculated as the Roughness Average of a surfaces measured microscopic peaks and valleys.
RMS is calculated as the Root Mean Square of a surfaces measured microscopic peaks and valleys. Each value uses the same individual height measurements of the surfaces peaks and valleys, but uses the measurements in a different formula.
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