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Surface Roughness Conversion Chart of Stainless Steel Tube









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 = Center Line Average in Microinches = Multiply Ra(µm) x 40

RMS = Root Mean Square in Microinches * (acceptable 1.1 - 1.7 factor) = Multi

ply CLA x 1.1

Rt = Roughness Total in Microns

N = New ISO grade scale numbers

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.
Related References:
1. ISO 1302 DIN 4768 Comparison of Surface Roughness Values
2. Electrical Discharge Machining EDM Roughness Comparator
3. Polishing Polished Seamless Stainless Steel Pipe Tube
4. Stainless Steel Tubes Surface Roughness Review
5. Stainless Steel Bright Annealing/Annealed Tubes
6. China USA Surface Roughness Standard Comparison
7. Surface Roughness Conversion Chart of Stainless Steel Tube
8. Stainless Steel Tube Surface Finish Types
9. Cleaning of Stainless Steel Tubes
10. Post weld cleaning and finishing of stainless steels
11. Care and maintenance of stainless steel
12. British and American standards for tolerances, surface finish and testing of stainless steel
13. Surface Finish Degree Comparison Table between Rz Ra RMS
14. Surface Roughness Table

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