Drilling cast iron. - Practical Machinist
Sep 15, 2011· If drilling by hand, say a #7 for a 1/4-20 tap you better predrill with a smaller size. Drilling by hand will not be rigid enough and the hole will be oversize. Usually the case if it is Mehanite type cast iron for a machine tool. Cheep import iron is easier to drill. At one time taps for cast iron were available. They had a different land ...