The oldest machining process
Abrasive grits are extremely hard ... Sand stone (quartz) –wheels used for hand grinding–cheap (SiO 2 + impurities) is not uniform and does not wear evenly. 2. Corundum and Emery –better uniformity and good for production (Natural Al 2 O 3 and Al 2 O 3 +Fe 3 O 4 +impurities) 3. Diamond and garnets –abrasive material (Hardest) most expensive (Carbon)hardness 10 on .