The Pointy Bit

Here is what it looks like in my shop when I am working on better understanding drill bits.

With any complex tool, there are multiple variables in play. With a handplane, the bed angle matters, but so does the chip breaker position and the bevel angle of the blade. With drill bits, the angles of the center spur and cutters matter, but so do other factors, such as the length of the center spur. When I need to know more about the impact of a given factor, I take it to the extremes. I made bits with huge center spurs, which slowed down the rate of feed, caused lots of heat build up and dulled my sensitivity to the cutting action. I made bits with a tiny center spur, which let the bit wander in the hole, tore up the sides of the mortise and advanced through the hole frighteningly fast.

Of course, one of the obvious benefits of a longer lead spur is the ability to drill at an angle. With other bits, you need to start perpendicular, or near so, to the surface and then move into position. A long lead spur remedies this or at least gives a good head start on being at the correct angle.