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