A twist drill is characterized by complex geometry which is a direct f
unction of the sharpening method used. This geometry has been studied
by several investigators attempting to understand the cutting mechanis
m of the drill point. Each cutting lip has been considered analogous t
o a single edge cutting tool in which the normal rake angle varies fro
m positive at the outerside to negative at the innerside. Optimum perf
ormance is achievable using straight cutting lips occurring only in ce
rtain combinations of flute shape and point angle. The chisel edge in
a conventionally ground drill has no true point. This is mainly respon
sible for geometric errors in drilling. In a double plane sharpened dr
ill point, a well defined chisel edge with four faces is produced. Thi
s point possesses a self centering action which facilitates drilling o
perations. The contribution of feed velocity to cutting velocity canno
t be neglected especially at the center where they are equal. This pap
er studies the working geometry of a double plane sharpened drill poin
t, taking the effect of feed velocity into consideration. The effect o
f feed can be neglected at the cutting lips without a remarkable error
, but cannot be neglected at the central zone.