Proper driving procedures are vital to obtain a firm joint. The recommended procedures are as follows:

1. Hold the head of the gun steady and at right angles to the work.

2. Press on the head of the gun hard enough to hold the rivet firmly against the work. Do not use a great amount of pressure unless it is necessary to bring the part being riveted into contact.

3. Squeeze the gun trigger and hold it until the rivet pin breaks, and then release the trigger. The next rivet should not be driven until the return action has caused the gun to latch. A distinct click will be heard.

The click indicates the gun is ready for the next installation cycle.

Figure 13-53 shows the complete installation of a self-plugging (mechanical lock) rivet.

The rivet is actually cold squeezed by the action of the pin head drawing against the hollow shank end. Shank expansion through the action of the extruding angle, blind head formation, and setting of the mechanical lock in the rivet head all follow in sequence and require but a fraction of a second. In some places, such as near the trailing edge of a control surface, there may not be sufficient space between the two surfaces to insert the rivet. In such cases, the pin may be forced into the hollow shank until the head of the pin touches the end of the shank.

Figure 13-53.-Self-plugging rivet (mechanical lock).

Since no further shank expansion will result, the drill hole should not be enlarged to provide a free fit of the already expanded rivet. To insert the rivet, you should use a hollow drift pin that will accommodate the rivet pin and the locking collar. See figure 13-54. This allows a driving force to be exerted on the head of the rivet. Drive the head into firm contact with the sheet, and then apply the rivet pull tool in the usual manner to upset the rivet.

Because of the mechanical lock feature of the pin and sleeve, the driven rivet is substantially the mechanical equivalent of a one-piece solid rivet.