Working on a steel bench block, use an awl to flare the opening of the tube. Rotate the awl at a slight angle in a circular motion, using even pressure to work the metal (Figure 1).
To make the opening look like a collar, use dapping punches in a circular motion to spread the flared opening. Start with a small punch and then switch to a larger punch (Figure 2).
Use the curved back of a steel burnisher in a rocking motion to push the edges of the collar tightly against the surface of the component you are riveting, rounding the edges off (Figure 3). Turn the piece over and repeat to flare and set the other end of the tube.