久久情操情在线免费播放

The drill bit is a cutting tool used in general drills or drilling machines to cut circular holes.  The basic principle of a drill bit is to rotate the cutting edge of the drill bit, cut the workpiece, and then remove drill cuttings from the drill slot.  The commonly used drill bits include twist drill, flat drill, center drill, deep hole drill and casing drill.  Reaming and countersinking cannot drill holes in solid materials, but they are also conventionally classified as drills.