Rotary
hammers are
heavy duty tools designed to bore holes in
concrete and
rock.
They consist of a normal
high powered drill machine with a main shaft that fits in an
airtight cylinder. The other end of the cylinder has a piston which is moved back and forth several times a second by complex
mechanical
gearing. The rapid pumping of the air in the cylinder causes the bit to hammer its way through the
material being drilled.
Since the force of
impact is delivered by air, they are sometimes known as electro-
pneumatic drills.
Some models have an option to
disengage the
rotation of the shaft and lock it in one position. This allows the drill to be used for
chipping and
breaking when fitted with a
chisel shaped bit.
The drill bits for rotary hammers are not usually held in chucks but use a system developed by
Bosch known as
SDS or
SDS-Max . They are tipped with
tungsten carbide tips and have a very long life.