Most drill troubles arise from inaccurate pointing. Correct drill pointing will to a great extent eliminate drill breakage and inaccurate holes. Drill pointing should be varied depending upon the materials to be drilled, but for general use, drills leave the factory sharpened to a 59° point angle (118° included angle), 9° – 15° clearance angle and with a chisel edge angle of 120° to 135°.
Since most operators do not have the skill required for good hand pointing, the use of standard drill pointing machines is highly recommended. Drills are machine pointed at the factory to a 118° angle to insure a correct and uniform point angle, equal cutting lips and correct chisel edge angle.
The point angle of a twist drill is the angle made by the cutting lip and the axis of the drill. For general purpose drilling a point angle of 59° (118° included angle) is recommended. The point angle may vary somewhat, one way or the other, but the variation should be uniform in both cutting lips. A twist drill point grinding gauge should be used for checking the point angle of both cutting lips.
CAUTION: When high speed steel drills are sharpened by dry grinding, care should be exercised to prevent overheating. If the drill does get too hot, do not cool in water, but let it cool by itself in air. Sudden cooling of high speed steel drills in water or other cooling mediums will usually produce grinding checks, which may result in chipping of the cutting lips or breaking of the drill point.
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