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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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