A cup tool consists of a top tool which is held on the work by means of a handle in a hole punched into the tool for the purpose, or held by an iron wire or wood handle twisted around the outside. The outline of the lower extremity of a cup tool is circular, and in the midst is a plano-convex reeess whose plane coincides with the flat bottom of the tool, also named the tool-face. The straight part of the tool is often much smaller in diameter than the cup-portion, for the purpose of making the tool as light as possible; one of this character is shown in Fig. 221.

The tools may be of several sizes, some having recesses of half an inch diameter, and others having recesses three inches diameter; the tools are thus adapted for chamfering nuts, shaping plano-convex bolt-heads, convexing extremities of pins and bolt stems, and also for general riveting purposes. If the object is to chamfer nuts, the cup tool is applied to the nut and struck with a sledge hammer, after the work is reduced to proper dimensions and shaped to the desired form, whether square or hexagonal. For bolt-heading, the cup tool is applied after the bolt is put into the header and roughly upset with hammering. If a cup tool is required for convexing extremities of long bolts or pins, the tool is held to the work and struck with a sledge hammer while the bolt is in the horizontal position on an anvil. A short bolt is stood upright upon the anvil, or upon an upsetting block, and the cup tool applied in a vertical position. For riveting purposes, cup tools are very small, having recesses only three-quarters of an inch, and for some work only three-eighths in diameter. Such tools are parallel, having their straight parts about as large in diameter as their cup-portions.

Cup tools are often forged of two pieces, one piece of iron for the stem, and the other piece being of steel for the cup part; the two being welded together. A preferable mode consists in forging the tool entirely of Bessemer steel, and the implement used for shaping the recess is a punch shown by Fig. 222. This punch is partly shaped with hammering, and afterwards filed and smoothed with emery cloth until the convex part is of the desired shape ; it is next hardened and fixed to a handle, and becomes fit for use. The mode of applying the punch consists in driving it into the solid metal at the place of the intended recess, the intended cup part being heated to about the softness of cold lead. The blows first given are with a sledge hammer, which is used till the recess is about the depth desired; and after one or two heatings, the finishing of the hollow is effected with a few blows of a light hammer, the work being a little cooler than red heat. In addition to this smoothing of the hollow with the punch, the cup may be further hollowed by lathe-turning; but in most cases such a troublesome process should be avoided, and the entire smoothing done with a properly shaped punch.

A cup tool may be also made in the form of a steam-hammer shaping block, in which case the recess may be formed by either casting or by punching with punches of proper sizes.