190 Agricultural Mechanics and Technology Systems
Copyright Goodheart-Willcox Co., Inc.
Drill bits are secured in the drill using a chuck,
or bit-holding device. The most common type of drill
chuck is the three-jawed Jacobs chuck, Figure 8-11. This
device requires the use of a geared tool known as a
chuck key to tighten and loosen the hold on the bit.
A common variation of this setup is the keyless
chuck. The user grips and turns the barrel of the
keyless chuck to tighten or loosen the chuck. Another
type of chuck retains the drill bit using a ball-and-
socket mechanism in a hole shaped to receive the
specially modifi ed bit shank.
Hammer Drills
A hammer drill is a tool that resembles a
conventional power drill but features a stronger
driving force. Hammer drills combine the torque of
a drill with a mechanism that works like someone
hitting the back of the drill with a hammer as you
drill the hole. They are useful for drilling holes in hard materials such as
concrete, masonry, and rock, Figure 8-12. The impact action is unnecessary
when drilling in wood, and it will damage many bits if used on metal. Some
hammer drills use Special Direct System (SDS) bits, which have heavily
reinforced shanks with a series of longitudinal slots. Spring-loaded keepers
fi t into the slots to eliminate the need for hand tightening.
The precautions for operating a hammer drill are much the same as
those for other power drills. However, the additional protection of a full-face
shield, hearing protection, and respiratory protection is recommended when
drilling concrete and masonry.
Impact Drivers
Impact drivers combine the torque of a power
drill with an impact mechanism much like a hammer
drill. In a hammer drill, however, the impact is applied
in a straight line parallel to the drill bit. The impact
in an impact driver applies additional torque, much
like hitting the back of a wrench with a hammer as the
bolt is being turned. Impact drivers have a two-stage
mechanism. At fi rst they work like a drill, applying
torque to a fastener until enough resistance is built
up to cause the hammering action to kick in. This
mechanism extends the life of the driver and reduces
damage to fasteners from excessive hammering.
Impact drivers are divided into two basic types
based on the intended use and the method for holding
attachments. The oldest type has a square driver designed to receive
reinforced impact sockets for driving nuts and bolts. Impact sockets look
ALEXANDER LEONOV/Shutterstock.com
Figure 8-11. Secure drill bits in a Jacobs chuck
by using the correct size chuck key to tighten the
locking ring at each of the three holes around the
chuck. This process must be done each time the
drill bit is changed. Do not forget to remove the
chuck key before drilling.
©iStock/Dan70
Figure 8-12. Hammer drills are heavy-duty tools
that are capable of delivering greater force and
power than standard power drills.