Figure 12-23.The web of the drill bit and how the drill
point is relieved by grinding.
be thinned to minimize the pressures required to make
the drill bit penetrate the material. The thinning must
be done equally to both sides of the web, and care must
be taken to ensure that the web is centered.
The DRILL POINT GAUGE (fig. 12-24) is the
tool most frequently used to check the drill point
during the sharpening operation.
Use a coarse wheel for roughing out the drill point
if much metal must be ground away. Complete the
operation on a fine wheel.
Many hand sharpening techniques have been
developed. The following are recommended:
1. Grasp the drill shank with the right hand and the
rest of the drill bit with the left hand.
2. Place the fingers of the left hand that are
supporting the drill bit on the grinder tool rest. The tool
rest should be slightly below center (about 1 inch on a
Figure 12-24.Using a drill point gauge.
3. Stand so the centerline of the drill bit will be at
a 59-degree angle with relation to the centerline of the
wheel (fig. 12-25), and lightly touch the drill lip to the
wheel in approximately a horizontal position.
4. Use the left hand as a pivot point and slowly
lower the shank with the right hand. Increase the
pressure as the heel is reached to ensure proper
5. Repeat the operation on each lip until the drill
bit is sharpened. DO NOT QUENCH HIGH-SPEED
STEEL DRILLS IN WATER TO COOL. LET THEM
COOL IN CALM AIR.
6. Check the drill tip frequently with the drill point
gauge to assue a correctly sharpened drill bit.
Secure a drill bit that is properly sharpened and
run through the motions of sharpening it. When you
have acquired sufficient skill, sharpen a dull drill bit.
To test, drill a hole in soft metal and observe the chip
formation. When proper] y sharpened, the chips will
come out of the flutes in curled spirals of equal length.
The tightness of the chip spiral is governed by the
RAKE ANGLE (fig. 12-26).
Figure 12-25.The correct position of the drill bit at the start
of the grinding operation. View is looking down on the
Figure 12-26.Rake angle of drill bit for ordinary work.