OPTIMUM
M A S C H I N E N - G E R M A N Y
Operation
Version 1.3.2 dated 2015-01-22
Page 18
Original operating instructions
DG20
US
4.3
General
4.3.1 Bit geometry
Bit grinding terms:
Chisel edge angle
Ψ
.
The chisel edge angle depends on the kind of
relief produced by grinding.
An angle of 55° is
best. Deviations from 55° increases the necessary drilling feed power. An unfavourable cut
ratio beneath the chisel edge (more "rubbing" than "cutting") requires a reduction of the
chisel edge of the bit for ductile steel or other ductile material if large drills are drilling
directly into solid material. This procedure is also called "drilling with pointed tooth". It could
also be performed by means of a drill bit grinder.
Pointed angle
ó.
The pointed angle is determined for various materials by experience, i.e. 118° for steel.
The angel
α
o
on the twist drill is called clearance angle or relief angle.
In general, a relief angle of 6° on the outer diameter rises up to over 20° on the point.
Fig.4-2: Drill bit geometry
