Machinery Repairman

Figure 5-37.—Grinding a twist drill for brass.
chisel-edge angle. Use a drill-point gauge (fig. 5-33)
and inspection to be sure you have met these four
requirements.
SHARPENING A TWIST DRILL TO
DRILL BRASS
To sharpen a drill to drill brass, hold the cutting
lip against the right side of the wheel as shown in
figure 5-37. Grind the flute slightly flat, in line with
the axis of the drill, to greatly reduce the included
angle of the cutting lip. This will give the drill the
scraping action needed for brass rather than the
cutting action used for steel. It will prevent the
tendency of the drill bit to be sucked into the hole
being drilled. This can be especially troublesome
when you drill through a pilot hole.
5-23
Figure 5-38.—Thinning the web of a twist drill.
THINNING THE WEB OF A TWIST
DRILL
Repeated sharpening shortens a drill and that
increases the web thickness at the point. This may
require web thinning.
To thin the web of a drill, hold the drill lightly to
the face of a round-faced wheel, as shown in figure
5-38, view A, and thin the web for a short distance
behind the cutting lip and into the flutes. This is
shown in figure 5-38, view B. Notice that the cutting
lip is actually (but only slightly) ground back,
reducing its included angle a small amount but not
enough to affect the operation of the drill.