The cutting action of the drill bit is its head, its cutting edge portion and the chisel blade as tool at work. To make the conical surface of the cutting portion does not touch the workpiece with the relief angle, clearance angle value, to be appropriately selected depending on the workpiece material.

1. chisel
Poor transverse sharp edge portion. Large diameter drill terrible for relatively coarse, chisel it big, addition, repair worn by chisel drill when regrinding, chisel has become large. To increase sharpness, or restore the initial grinding and get the same sharpness, the need for cross-edge grinding.
 
2. The margin in the order processed guiding hole wall, leaving the processing can be correctly performed. But this case, if the friction is large and the hole wall, the drill bit will overheat, power consumption will be too large. So, usually from the drill head toward the shank with a small taper, it is called inverted cone, about every 100 mm to about 0.04 ~ 00.1 mm.

3. spiral groove
Is provided for discharging chips, and its size should be the chips can be discharged smoothly, and shall be provided with a helix angle. Its groove helix angle, the type of workpiece material should vary. Of hard materials, the angle is smaller, for soft materials, the angle should be large. Working with ordinary steel drill bit, helix angle of about 30 degrees.
 
4. The top angle drill
Hour angle drill, although relatively easy to cut into the workpiece, but its drawback is due to the cutting edge becomes longer, the required power increases, and the rake angle of the cutting edge is reduced, shortened life expectancy. Therefore, the top of the drill tip in the hole machining of soft material. Typically general steel materials, vertex with about 120 degrees.