_Hammers._--To deliver the blow upon a rock drill, hammers and sledges are used. The distinction between a hammer and a sledge is founded on dimensions only: the hammer being intended for use in _one_ hand, is made comparatively light and is furnished with a short handle, while the sledge, being intended for use in _both_ hands, is furnished with a much longer handle and is made heavier. The striking face of the blasting sledge should be flat, to enable the striker to deliver a direct blow with certainty upon the head of the drill; and to facilitate the directing of the blow, as well as to increase its effect, the mass of metal composing the head should be concentrated within a short length. To cause the sledge to fly off from the head of the drill in the case of a false blow being struck, and thereby to prevent it from striking the hand of the man who holds the drill, the edges of the striking face should be chamfered or bevelled down till the diameter is reduced by nearly one-half. This requirement is, however, but seldom provided for.
The head of a sledge is of iron; it consists of a pierced central portion called the “eye,” and two shanks or “stumps,” the steeled ends of which form the striking faces or “panes.” The form of the head varies in different localities, but whatever the variations may be, the form may be classed under one of four types or “patterns.” A very common form is that shown in Fig. 10 and known as the “bully” pattern. By varying the width, as shown in Fig. 11, we obtain the “broad bully,” the former being called for the sake of distinction the “narrow” bully. Another common form is the “pointing” pattern, represented in Fig. 12. The form shown in Fig. 13 is designated as the “bloat” pattern; and that given in Fig. 14 the “plug” pattern. Each of these forms possesses peculiar merits which renders it more suitable for certain uses than the others. The same forms are used for hammers. The eye is generally made oval in shape, but sometimes, especially with the bloat pattern, it is made circular, as shown in Fig. 13. The weight of a sledge head may vary from 5 lb. to 10 lb., but a common and convenient weight is 7 lb. The length of the helve varies from 20 inches to 30 inches; a common length for blasting sledges is 24 inches. The average weight of hammer heads is about 3 lb., and the average length of the helve 10 inches.