BENCH TIP FROM ALAN REVERE
Soldering posts on earring is an everyday operation for many jewelers. However, rather than guessing where to place the post, try using a 1 mm ball bur to make a small indentation where it should go.
This is not so easy to do. Take the earring in one hand and the flex-shaft, with the bur, in the other. (Make sure your hands are well braced.) Slowly and carefully lower the spinning bur to the metal, sideways. Do not apply force, or the bur will skid out of control. Once you've created an indentation, turn and bur straight into the metal from above.
To prepare the post, use a cup bur to shape the end into a corresponding convex hemisphere. Now flow some solder into the depression on the back of the setting. Bring the rounded end of the post into contact with the depression as the reheated solder flows; it should drop into perfect position. When finished, give the newly soldered earring posts a twist to ensure they are secure.
This procedure has accomplished two important tasks: It has located the post in the center of the earring, and provided a much stronger solder seam than a simple butt joint.