Sneaky Soldering

Getting an ultra clean weld in a mixed-metal design

By Bob Lynn

Has a mixed-metal job that doesn’t have any tolerance for cleanup after soldering ever landed on your bench? Because of the design, you can’t use rivets to hold the yellow and white gold pieces together, and laser welding would require a huge amount of work.

If you ever come across a situation where you can’t afford any of the gold solder that holds an inlay piece of yellow gold in place to show up on the white gold component, here’s a little trick. The example shown here is very basic, but the technique can be applied to any design that requires a clean weld but doesn’t have any cleanup tolerance.

1. In this example, you need to inlay a piece of yellow gold into a white gold band without any solder showing once you are done. Because the grooves in the ring surface are high polish and butt up against the inlay, there is no way to bright cut the junction between the two metals. There’s also no way to get a polishing tool on the end of the grooves.

2. This CAD drawing indicates the tight fit. You can’t put a piece of solder at the joint between the two metals because the solder will show on the white gold.

3. You can’t put a piece of solder under the inlay in the socket because the fit is too tight.

4. To solve the problem, use a ball bur to make several small depresseions in the bottom of the inlay.

5. Put small bits of solder into the depressions and flow the solder to fill them in. Once it cools, file the solder flush with the surface. You can also chamfer the edges of the bottom surface of the inlay very slightly to make a tiny clearance for the solder to flow.

6. Fit the inlay back in the socket so it sits snugly. Flux and heat the ring to the appropriate temperature to allow the solder to flow, but don’t get it so hot that the liquid is drawn out of the joint.

7. Let it cool, then clean and polish. When done correctly, this trick provides a full-strength weld holding the inlay in place with no visible solder.