Question 656General Subjects - Assistant Engineer

You are correct, the answer is A) included point angle. The included point angle of a twist drill refers to the angle between the two cutting edges at the tip of the drill. For drilling harder metals, a larger included point angle is required to provide more clearance for the cutting edges and prevent the drill from binding or wandering in the hole. The other options are incorrect because: B) cutting speed is not directly related to the hardness of the metal, C) the drill diameter is typically selected based on the desired hole size, and D) lip clearance is more related to the drill geometry rather than the workpiece material hardness.