This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
The owner of a private workshop has need for taps and occasionally wishes to make them, not because they are cheaper, but for the sake of experience or to get some special thread. In cutting the flutes, whether it be by hand or in a shaper, it is a good plan to give the flutes an angle, that is, to cut them, not parallel with the axis of the tap, but at an angle of 5 to 15 deg. with the center line. This makes the tap cut easier, giving it a wedge action instead of just simply pushing the metal off. The same method applies to counterbores and countersinks, which, when so made, take less power to drive.