Bucking bars are tools used to form bucktails (the head formed during riveting operations) on rivets. They come in many different shapes and sizes, as shown in figure 13-4. Bucking bars are normally made from an alloy steel similar to tool steel. The particular shape to be used depends upon the location and accessibility of the rivet to be driven. The size

Figure 13-4.-Bucking bars.

and weight of the bar depend on the size and alloy of the rivet to be driven. Under certain circumstances, and for specific rivet installations, specially designed bucking bars are manufactured locally. These bars are normally made from tool steel. The portion of the bar designed to come in contact with the rivet has a polished finish. This helps to prevent marring of formed bucktails. Bucking-bar faces must be kept smooth and perfectly flat and the edges and corners rounded.

NOTE: Never hold a bucking bar in a vise unless the vise jaws are equipped with protective covers to prevent marring of the bucking bar.

A satisfactory rivet installation depends largely on the condition of the bucking bar and your ability to use it. If possible, hold the bucking bar in such a manner that will allow the longest portion of the bar to be in line with the rivet. You should hold the bucking bar lightly but firmly against the end of the rivet shank so as not to unseat the rivet head. The inertia of this tool provides the force that bucks (upsets) the rivet and forms a flat, headlike bucktail.