and C are used in either the hand drill, portable electric
drill, or drill press. Type B produces a rough surface
but cuts the fastest. Type C produces a smooth seat and
is the countersink of choice for finish work.
There are many types of combination counter-
sinks and counterbores, but they all perform the same
function. These tools make the pilot hole, shank
clearance, and countersink in one operation. The
combination counterbore performs the same tasks as
the combination countersink and bores a plug hole for
wooden plugs. Combination countersinks and
counterbores range in size from #6 to #12 and
accommodate wood screw sizes #5 to #14.
The particular size of wood screw each counter-
sink and counterbore accommodates determines the
size of the countersink or counterbore. Use both with
the hand drill, portable electric drill, and drill press.
Figure 5-23.--Types of points on the metal-cutting chisel.
the job. Be sure to use a hammer that matches the
chisel; that is, the larger the chisel, the heavier the
There are many types of metal-cutting tools used
hammer. A heavy chisel will absorb the blows of a
by skilled mechanics of all ratings. As you become
light hammer and will do virtually no cutting. As a
better acquainted with your rating, you will probably
general rule, you should hold the chisel in your left
discover many tools that you use for cutting metal that
hand with the thumb and first finger about 1 inch from
are not described in this chapter. In this chapter, only
the top. You should hold it steady but not tight. Your
the basic hand metal-cutting tools (chisels, hacksaws,
finger muscles should be relaxed, so if the hammer
and files) will be discussed due to their frequent but
strikes your hand it will permit your hand to slide
down the tool and lessen the effect of the blow. Keep
your eyes on the cutting edge of the chisel, not on the
head, and swing the hammer in the same plane as the
Chisels are tools that can be used for chipping or
body of the chisel. If you have a lot of chiseling to do,
cutting metal. They will cut any metal that is softer
slide a piece of rubber hose over the chisel. This will
than the materials of which they are made. Chisels are
lessen the shock to your hand.
made from a good grade tool steel and have a hardened
When using a chisel for chipping, always wear
cutting edge and beveled head. Cold chisels are
goggles to protect your eyes. If other people are
classified according to the shape of their points, and
working close by, see that they are protected from
the width of the cutting edge denotes their size. The
flying chips by erecting a screen or shield to contain
most common shapes of chisels are flat (cold chisel),
the chips. Remember that the time to take these
cape, round nose, and diamond point (fig. 5-23).
precautions is before you start the job.
The type of chisel most commonly used is the flat
After numerous blows to the head of a chisel, it
cold chisel that cut rivets, split nuts, chip castings, and
will begin to deform. This deformation is called
cut thin metal sheets. The cape chisel is used for
special jobs like cutting keyways, narrow grooves, and
mushrooming and creates a very dangerous situation.
square corners. Round-nose chisels make circular
If the head of a chisel mushrooms excessively, bits of
grooves and chip inside comers with a fillet. Finally,
the head will begin to fly off when struck with a
the diamond-point is used for cutting V-grooves and
hammer. These small bits of metal have the force of
shrapnel from a hand grenade and could cause as much
damage. Simply keep the head of a chisel ground down
As with other tools, there is a correct technique for
to remove this dangerous situation.
using a chisel. Select a chisel that is large enough for