DRILL

TWIST DRILL

Parts of Twist Drill

TWIST DRILL:

It has a cylindrical body on which the grooves are cuts. These grooves are called flutes.
It is an end cutting tool with two, three or four cutting lips.
The drill is held by a shank. The shank may be parallel or tapered.

(a) LIP RELIEF ANGLE:

Lip relief angle varies 12 to 15 degrees.
This angle may be increased for drilling soft material under heavy feeds
It is the angle formed by the flank and a plane at right angles to the drill axis.

(b) HELIX OR RAKE ANGLE:

Its usual value of angle is 30 degrees.
A drill with low helix angle is used in drilling brass where as a drill with high helix angle is used in drilling aluminium.
It is the angle formed by the leading edge of the land with a plane having the axis of the drill.

(c) TAPERED SHANK

(d) FLUTE LENGTH

(e) BODY

(f) NECK

(g) SHANK LENGTH

(h) OVER ALL LENGTH

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