November 7, 2014 admin

Polished finishes

So your customer has given you a surface finish value that you have to hit and you are not sure about the value in your normal standard.
Not to worry. There is a way.

Types of finishes:

Types of
Finishes
Current SPI
Finish Numbers
Description and
Previous Finish Numbers
 Ra, µm
Diamond
#3 Diamond Buff
A1
Lens / Mirror
#1 0.025
#6 Diamond Buff
A2
High Polish parts
#2 0.05
#15 Diamond Buff
A3
High Polish parts
0.1
Paper
600 Grit
B1
Medium Polish
#3 0.2
400 Grit
B2
Medium Polish
0.4
320 Grit
B3
Medium – Low Polish
0.8
Stone
600 Stone
C1
Low Polish
#4 1.6
400 Stone
C2
Low Polish
3.2
320 Stone
C3
Low Polish
6.3
Dry Blasted
#11 Glass Bead
D1
Satin finish
#5 12.5
240 Aluminum Oxide Blast
D2
Dull Finish
25
#24 Aluminum Oxide Blast
D3
Dull Finish
50

Comparison between standards:

N = New ISO scale numbers
Rt = Roughness, total in microns
Ra = Roughness, average in microns
CLA = Centre Line Average in microinches
RMS = Root Mean Square in mircoinches

N Rt Ra CLA RMS Cut-off
Inches
length mm
1. 0.3 0.025 1 1.1 0.003 0.08
2. 0.5 0.05 2 2.2 0.01 0.25
3. 0.8 0.1 4 4.4 0.01 0.25
4. 1.2 0.2 8 8.8 0.01 0.25
5. 2.0 0.4 16 17.6 0.01 0.25
6. 4.0 0.8 32 35.2 0.03 0.8
7. 8.0 1.6 63 64.3 0.03 0.8
8. 13 3.2 125 137.5 0.1 2.5
9. 25 6.3 250 275 0.1 2.5
10. 50 12.5 500 550 0.1 2.5
11. 100 25.0 1000 1100 0.3 8.0
12. 200 50.0 2000 2200 0.3 8.0

 

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