Hammer drilling machine

1 Hammer drilling machine (sectioned); 1 short hollow drill; 1 short twist drill

In this type of percussive drill the action is the primitive one of striking a chisel with a hammer, only that in place of the hammer there is a free piston reciprocating in a cylinder. The idea was first adapted to mining at Mansfield, in Germany, but it was not till a satisfactory method of rotating the chisel was brought out that the drill became a success.

The hammer drill occupies a field which the larger piston drill does not economically fill. It is a hand tool which can be used in narrow veins, small stopes, &c. ; it delivers a large number of light blows which are as effective as a smaller number of heavy blows, but not so destructive of the drill steel. It drills small holes which are economical in explosive and its speed enables it to oust hand drilling.