Angle Drills
The hammer action is provided by two cam plates that make the chuck
rapidly pulse forward and backward as the drill spins on its axis. This
pulsing (hammering) action is measured in Blows Per Minute (BPM) with
10,000 or more BPMs being common. Because the combined mass of the chuck
and bit is comparable to that of the body of the drill, the energy
transfer is inefficient and can sometimes make it difficult for larger
bits to penetrate harder materials such as poured concrete. The operator
experiences considerable vibration, and the cams are generally made
from hardened steel to avoid them wearing out quickly. In practice,
drills are restricted to standard masonry bits up to 13 mm (1/2 inch) in
diameter. A typical application for a hammer drill is installing
electrical boxes, conduit straps or shelves in concrete.In contrast to the cam-type hammer drill, a rotary/pneumatic hammer
drill accelerates only the bit. This is accomplished through a piston
design, rather than a spinning cam. Rotary hammers have much less
vibration and penetrate most building materials. They can also be used
as "drill only" or as "hammer only" which extends their usefulness for
tasks such as chipping brick or concrete. Hole drilling progress is
greatly superior to cam-type hammer drills, and these drills are
generally used for holes of 19 mm (3/4 inch) or greater in size. A
typical application for a rotary hammer drill is boring large holes for
lag bolts in foundations, or installing large lead anchors in concrete
for handrails or benches.
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