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Surface









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).

Surface roughness is the measure if the finer surface irregularities in the surface texture. These are the result of the manufacturing process employed to create the surface. Surface roughness Ra is rated as the arithmetic average deviation of the surface valleys and peaks expressed in micro inches or micro meters. ISO standard use the term CLA (Center Line Average). Both are interpreted identical.



Ra
micro-meters
Ra
micro-inches
RMS
CLA
(N)
Rt
N
Cut-Off Length
in.
mm
0.025
1
1.1
1
0.3
1
0.003
0.08
0.05
2
2.2
2
0.5
2
0.01
0.25
0.1
4
4.4
4
0.8
3
0.01
0.25
0.2
8
8.8
8
1.2
4
0.01
0.25
0.4
16
17.6
16
2.0
5
0.01
0.25
0.8
32
32.5
32
4.0
6
0.03
0.8
1.6
63
64.3
63
8.0
7
0.03
0.8
3.2
125
137.5
125
13
8
0.1
2.5
6.3
250
275
250
25
9
0.1
2.5
12.5
500
550
500
50
10
0.1
2.5
25.0
1000
1100
1000
100
11
0.3
8.0
50.0
2000
2200
2000
200
12
0.3
8.0

Conversions (math):

CLA (micro inches) = Multiply Ra(µm) x 40

RMS * (acceptable 1.1 - 1.7 factor) = Multi

ply CLA x 1.1