Reaming is always preceded by drilling or counterboring the hole. The drill or counterbore diameter should be selected to leave an appropriate machining allowance: 0.25–0.50 mm (0.010–0.020 in) for rough reaming and 0.05–0.15 mm (0.002–0.006 in) for finish reaming. The depth of cut corresponds to the thickness of the material removed and is equal to one-half of the total diameter allowance.
