• Jack hammer is a basic tool of the percussion type of rock drills.
  • Jack hammers are hand held, air operated percussion type drills. A complete jack hammer consists of a hammer, drill steel and bit.
  • The jack hammers are generally used for holes up to 3 m in depth, though they can be used to drill holes up to 6 m deep.
  • The heavier hammers may drill holes up to 6 mm in diameter.
  • Drill steels are usually available in lengths of 60 cm, 120 cm,180 cm and 240 cm lengths.

The jack hammers are generally classified according to their weight as follows:

• Sinkers: These are hand held unmounted drills generally ranging in weight between 7 kg to 40 kg. Small sinkers between 7 to 9 kg weight are sometimes called as plug drills. Sinkers are used for drilling blast holes downwards.

• Leg drill : Similar to sinker but mounted on a pneumatic ram or leg which can be jammed against a rock on the floor to drill a hole horizontally. These are used for drilling blast holes in tunnels.

• Stopper: Similar to leg drill but with the air leg made as a part of the drill's construction fixed in line with the drill steel. With the foot of the leg on the floor, the steel points vertically up to the roof. These are used for the roof bolting or raise blasting.

• Drifters: These are rock drills of jack hammer type but are heavy in weight i.e. between 45 kg to 70 kg or more. These are used for drilling bigger size holes usually 7.5 to 10 cm in diameter. These can be used for drilling in harder rocks at greater speed and are normally employed for excavation work in mines and tunnels.

• Wagon drills: It is a drifter mounted on a wheeled frame. The wheels have swivel joints with the chassis so that turning is possible in restricted space and the frame can be turned irrespective of direction of the wheels. These wagon drills are suitable for drilling deep holes in hard rocks.