Hammers differ in weight more than in form. The common shape of hammer used is the ball pene hammer shown in Fig. 7.
In weight they vary from five or six ounces to three or four pounds, and are used according to the work in hand. The effect of a blow from a hammer depends upon the weight and the speed. A heavy hammer produces a deeper effect upon the metal than a light one. The reason is that the force of a light blow is easily absorbed by the metal in the immediate vicinity of the surface.
A heavy blow cannot be absorbed as readily, hence the metal shows the effect for a greater distance from the surface. This is illustrated by the rivets shown in Figs. 8 and 9. In Fig. 8 the metal at the end of the rivet is turned over by blows from a light hammer. In Fig. 9 where a blow was struck by a heavy hammer, the metal is upset for nearly the whole length of the rivet. There is no sudden enlargement at the end, but an increase in size for some distance there-from.
Another form of hammer is shown in Fig. 10. This is the sledge hammer, and is used for striking heavier blows than can be given with the ball pene hammer of Fig. 7. The peen of this hammer is straight and rounded on the edge. Such hammers weigh from five to twenty pounds.
In the fitting of the handle to the head great care should be taken. Hammer handles are made elliptical in cross section. The major axia of tin's ellipse should exactly coincide with that of the eye of the head. The reason is that the hand naturally grasps the handle so that its major axis lies in the direction of the line of motion. Hence, unless the handle is properly fitted in this particular, there will he constant danger of striking a glancing blow. The handle should also sland at right angles to a center line drawn from the ball of the pene to the face. The eye in the head is usually so set that the weight on the face side is greater than that on the pene. The effect of this is to so balance the tool that heavier and more accurate blows can be struck than if the, weight were evenly balanced on each side of the eye.