learn how to hold a drill at the correct angle, another
person should sight the angle before starting the drill.
Another common mistake is to put too much
pressure on the drill. Pushing or crowding a drill may
break the drill point. It could cause the drill to plunge
through the opposite side of the sheet and leave rough
edges around the hole. It could also cause the drill to
side slip on the metal, causing hole elongation.
The drill should not be stopped immediately upon
breaking through. It should continue to be inserted
for approximately half its length while still running,
and then withdrawn.
This operation requires
judgment and skill because it is very easy to ream the
hole. If this is done properly, cleaner holes will result.
Pneumatic drills are available in various sizes and
shapes. The drills are designed to provide a rotary
shaft that is equipped with a chuck capable of holding
a drill bit. Most are powered by a vane air motor, and
the speed is adjustable by using the variable restrictor
built into the motor body. Normal maintenance of the
unit requires only a clean, dry air supply and periodic
lubrication of the vane assembly. Lubrication can be
accomplished by inducing a small amount of light oil
into the air supply. The two most used types are the
straight and the pistol grip. See figure 13-12.
The angle-drive drills are attached to the drill
motor by an adapter assembly or clamped into the
existing drill chuck. They are available with a ridged
or flexible drive shaft and come in several different
head angles. See figure 13-13. These units are
designed to be used as an extension of the drill motor
in hard to reach areas. The drill motor should never
be started unless you have positive control of the
The flexible shaft is commonly
referred to as a snake drill. The drill chuck normally
requires a wrench to tighten the jaws or it may require
a special threaded drill bit.
Special tools are not normally part of an
individuals toolbox. These tools are normally
maintained in a central toolroom and signed out when
Figure 13-13.Angle-drive drills.