Comparing Abrasive Systems

It is all very well to say that sandpaper is 100, 200, 600 grit etc, but what does it actually mean? When you talk about waterstones being 1000, 2000, 6000 etc, is that the same as 1000, 2000, 6000 sandpaper?

Unfortunately no! The way that I prefer to ensure I’m comparing apples with apples is to look at the size of the abrasive material itself. This at least should be a uniform way of comparing different abrasives. In other words, I may start sharpening on a diamond stone, transfer to sandpaper, and finish on waterstone. Ok, I may not jump around like this, but there is no reason why you can’t, once you understand the micron size of the abrasive.

I’ve listed here the 2 main sandpaper designations, and the actual micron size of the particles. This will then allow other mediums to be compared.

 
ISO/FEPA Grit designation
CAMI Grit designation
Average particle diameter (┬Ám)
MACROGRITS
Extra Coarse (Very fast removal of material)
P12
 
1815
P16
 
1324
P20
 
1000
P24
 
764
 
24
708
P30
 
642
 
30
632
 
36
530
P36
 
538
Coarse (Rapid removal of material)
P40
40
425
 
50
348
P50
 
336
Medium (sanding bare wood in preparation for finishing)  
60
265
P60
 
269
P80
 
201
 
80
190
Fine (sanding bare wood in preparation for finishing)
P100
 
162
 
100
140
P120
 
125
 
120
115
Very Fine (final sanding of bare wood)
P150
 
100
 
150
92
P180
180
82
P220
220
68
MICROGRITS
Very Fine (sanding finishes between coats)
P240
 
58.5
 
240
53.0
P280
 
52.2
P320
 
46.2
P360
 
40.5
Extra fine  
320
36.0
P400
 
35.0
P500
 
30.2
 
360
28.0
P600
 
25.8
Super fine (final sanding of finishes)  
400
23.0
P800
 
21.8
 
500
20.0
P1000
 
18.3
 
600
16.0
P1200
 
15.3
Ultra fine (final sanding of finishes)
P1500
800
12.6
P2000
1000
10.3
P2500
 
8.4

Waterstones micron sizes are:

1000 : 14
2000 : 7.5
4000 : 3
6000 : 2
8000 : 1.2

So from this we can see that a 1000 waterstone is actually comparable to between a 1200 and 1500 grit sandpaper. And that my 6000 grit waterstones are VERY smooth!

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