Ballnose drill with variable cutting angle.

摘要

The cutting end (7) or tip of a twist drill bit (1) has a hemispherical overall shape and has four cutting lips, two (8, 9) of which are arranged flight to flight at the top S of the drill bit. The cutting angle of the cutting edge of the said lips alters and varies from zero degrees at the top S up to a value determined experimentally as a function of the material to be machined at the point P, at the end of the diameter d of the drill bit.