SURFACE FINISH COMPARISON CHART |
RA is the arithmetic average deviation of the surface valleys and peaks and is often used to specify the roughness of a machined surface. RMS is the root mean square average of the profile height deviations from the mean line of the surface and is mostly used for optical surfaces. |
The term Micro means millionth. So 1 micrometer is 1 millionth of a meter, or .000001 meter. Likewise 1 microinch is 1 millionth of an inch, or .000001". The term "Micron" refers to 1 millionth of a meter, which is also equivalent to 1 thousanth of a millimeter (.001 mm), and is represented by the greek symbol μ. Ra microinch ( μ" ) is basically the same as the CLA scale, or centerline average. |
Some Useful Conversions: |
Inch = " or in |
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1 microinch (μ") = 0.0254 micrometers (or microns) |
Micron = µ |
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1 microinch (μ") = 0.0000254mm |
Micro Inch = µ" |
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0.001" = 0.0254mm |
Micrometer = µm |
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Millimeter = mm |
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Below are equivalent values on various surface measurment scales, and the manufacturing methods capable of producing these finishes. |
New ISO scale numbers |
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1. |
2. |
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4. |
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12. |
RMS Microinches ( μ" ) |
0.5 |
1.1 |
2.2 |
4.4 |
8.8 |
17.6 |
35.2 |
64.3 |
137.5 |
275 |
550 |
1100 |
2200 |
RMS Micrometers ( μ m ) |
0.013 |
0.027 |
0.055 |
0.11 |
0.22 |
.44 |
.88 |
1.6 |
3.44 |
6.88 |
13.75 |
27.5 |
55 |
CLA or Ra microinch ( μ" ) |
0.5 |
1 |
2 |
4 |
8 |
16 |
32 |
63 |
125 |
250 |
500 |
1000 |
2000 |
Ra micrometer ( μ m ) |
0.012 |
0.03 |
0.05 |
0.1 |
0.2 |
0.4 |
0.8 |
1.6 |
3.2 |
6.3 |
12.5 |
25 |
50 |
Sand Casting |
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Hot Rolling |
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Forging |
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Permanent-Mold Casting |
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Investment Casting |
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Extruding |
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Cold Rolling |
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Diecasting |
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Flame Cutting |
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Sawing |
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Planing |
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Drilling |
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EDM |
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Milling |
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Laser Cutting |
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Reaming |
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Broaching |
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Turning and Boring |
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Tumbling |
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Roller Burnishing |
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Grinding |
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Honing |
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Electro-Polishing |
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Polishing |
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Lapping |
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Superfinishing |
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