The possibility of soldering eyeglass frame hinges onto metal frames depends entirely on the metals of which the frames and hinges are made. A solder made of roughly 95 per cent tin and 5 per cent silver will bond copper, silver, gold, brass, and steel. However with other materials such as titanium and stainless steel you may need to braze or weld the hinges on. Remove the lenses and any part of the frame that could be damaged by the heat. The solder joint must not move while you are soldering or while the solder hardens.
Clean any corrosion off of the surface to be soldered with fine emery cloth. Be careful not to mar the finish in other areas that may spoil the appearance of the frame.
Clean the areas of the frames and hinges where the solder will attach them together. Use solvent and a rag to clean away any oil, grease, or fingerprints.
Apply soldering flux to the areas on the frame and hinges where you will solder.
Place the frame in a vice and use clamps to hold the hinge in place. The hinge must fit flush because the solder will not fill gaps. And it must remain steady throughout the soldering process. If the joint moves even slightly while the solder cools, the joint will fall apart with the slightest pressure. It must remain perfectly still.
Heat the joint with the torch for a few seconds, and then touch the solder to the joint. The solder should melt and flow into the joint by capillary action. If the solder doesn't melt instantly when touched, the joint isn't hot enough yet.
Wait for the solder to cool before moving the frames. The solder should harden within 10 seconds, but the frames may remain too hot to touch for a longer time, depending on the size and thickness of the frame and hinges.
Hold the frames gently in a rag while loosening the vice and clamps. When you are sure the frames are cool enough to touch, clean the soldered joint with the solvent and rag to remove any residue from the soldering flux.
Look in jewellery maker's supply shops to find your torch, vice, and clamps. For a stronger solder joint, use a solder made with a higher silver content; you will have to heat this more to get it to melt.
Solders containing lead or cadmium raise environmental concerns. If you decide to use them, work in a well ventilated area, don't breathe the fumes, and wear protective goggles.