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 |
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| 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:
