Rivets must be removed and replaced if they show even the slightest deformity or lack of alignment. Reasons for replacing rivets are as

Figure 13-46.-Rivet dimensions before and after bucking. 

follows: rivet marred by bucking bar or rivet set; rivet driven at slant or shank bent over; rivet too short, causing the head to be shallow; rivet pancaked too flat from overdriving; sheets spread apart and rivet flashed between the sheets; two rivet heads not in alignment; and head of countersunk rivet not flush with outside surface or driven below surface. Examples of these incorrectly driven rivets are shown in figure 13-47.

When you are removing rivets, be careful not to enlarge the rivet hole. This will require you to use a larger size rivet for replacement. To remove a rivet, file a flat surface on the manufactured head. It is always preferable to work on the manufactured head rather than on the one that is bucked, since the former will always be more symmetrical about the shank. Indent the center of the filed surface with a center punch, and use a drill of slightly less than shank diameter to drill through the rivet head. Remove the drill and, with the other rivet end supported, pry or lightly tap off the head with a drift punch. If the shank is too tight after the removal of the head, the shank should be drilled out. However, if the sheet is firmly supported from the opposite side, the

Figure 13-47.-Incorrectly driven rivets.

shank may be punched out with a drift punch. See figure 13-48.

The removal of flush rivets requires slightly more skill. If the formed head on the interior is accessible and has been formed over heavy material, such as an extruded member, the formed head can be drilled through and sheared off. If the material is thin, it may be necessary to drill completely through the shank of the rivet, and then cut the formed head with diagonal-cutting pliers. The remainder of the rivet may then be drifted out from the inside.