Page 152 - Turner 1st sem Practicals

Re-sharpening a twist drill
Objective : This shall help you to
• re-sharpen a twist drill.
A twist drill can be successfully sharpened on a bench or
pedestal grinder by adopting the following procedure.
Check that the surface of each wheel is running true and
that the wheels are dressed clean.
Ensure that the tool-rest are adjusted correctly
and tightened.
Wear safety goggles.
Stand in a comfortable position in front the machine.

Hold the drill at about one quarter of its length from the
point, between the thumb and the first finger of the right
hand. (Fig 1)

Watch the cutting edge against the wheel. Note that, as
the shank, swings down, the cutting edge comes slightly
upwards and away from the wheel face. (Fig 5)

Keep both elbows against the side.
Position yourself in such a way that the drill makes an
angle of 59° to 60° to the wheel face. (Fig 2)

Apply a slight foward motion to your hands.

This will bring the flank of the point against the wheel to
produce a lip clearance.

Coordinate the three movements of swinging
down, twisting clockwise and forward
movement. These movements should not be
heavy movements. If they are performed
correctly, they will produce a cutting edge that
has the correct lip clearance and cutting angle.

Hold the drill level. Twist it until one cutting edge is hori- Practice these movements against a stationary wheel,
zontal and parallel to the wheel face. (Fig 3) using a new or correctly sharpened drill.
Swing the shank of the drill slightly downwards and to the Notice how only a small movement is required to produce
left with the left hand. The right hand is on the tool-rest. the required clearance.
(Fig 4) Also note that, if the drill is twisted too far, the other cutting
edge will swing down to contact the wheel face.
Producltion & Manufacturing : Turner - Exercise 1.3.42 139