shadow

Grit

The grit is chosen according to the quantity of material that has to be removed and the roughness you want to reach. Carats being equal, a fine grit presents a larger number of cutting edges on the rim; therefore the wheel is harder, denser and less malleable. It is therefore necessary to find the right combination grit-size/concentration, to allow dispersion of the chips; to avoid chip build up, or clogging. The grit is designed according to its country of origin.The european FEPA Standard classifies the grit according to its average diameter. The charts USA-mesh and DIN 848-65 are also very popular.The following chart allows a comparison of the different classifications:

 

molemab INOTECH
F.E.P.A
DIAMANT
molemab INOTECH
F.E.P.A
CBN
US-Standard
ASTM-E-11-70
DIN mesh sizes 848 (1980)
ISO 6106
DIN 848 (1965)
close wide close wide close wide close wide
D 301   B 301   50/ 60   300/ 250
D 280
D 220
D 180
D 140
D 110
D 90
D 65
D 55
D 45
D 35
 
D 250
D 150
D 100
D 70
D 50
D 30
D 251 D 252 B 251 B 252 60/ 70   250/ 212
D 213 B 213 70/ 80   212/ 180
D 181   B 181   80/ 100   180/ 150
D 151   B 151   100/ 120   150/ 125
D 126   B 126   129/ 140   125/ 106
D 107   B 107   140/ 170   106/ 90
D 91   B 91   170/ 200   90/ 75
D 76   B 76   200/ 230   75/ 63
D 64   B 64   230/ 270   63/ 53
D 54   B 54   270/ 325   53/ 45
D 46   B 46   325/ 400   45/ 38
             

 

Grit finer than D (B) 46 is selected by sedimentation, not by sieving. This grit is therefore designated through tolerances, as shown below:

 

Grit in µ 35-45 30-40 25-35 20-30 15-25 10-20 8-15 6-12 4-8 4-6 2-4 1-3 1-2
DIAMANT

CBN
D40 D35 D30 D25 D20 D15 D12 D9 D7 D5 D3 D2 D1
  B35 B30     B15     B7   B3    
F.E.P.A. M40     M25   M16   M15 M6,3 M4,0 M2,5 M1,6 M1,0

 

Three factors affect the choice of grit: quantity of material to be removed, surface-finish and wheel life. Removal and wheel-life depend on the adjustment when swing-grinding, and on pass and feed depth when plunge-grinding. A wheel used properly shows a penetration depth equal to 1/5 - 1/8 of the grit dimension. If the level of roughness needed is known, it is possible to choose the right grit using the following chart: