Q: I’ve got a soldering fixture made from graphite, in the shape of a ring mandrel. The problem is that it takes forever to get a silver ring hot enough for the solder to flow. Am I using it wrong?
The reason these graphite mandrels can be hard to use is that graphite is an exceptionally good conductor of heat, so the graphite drains the heat away from the metal almost as fast as, say, an aluminum or silver mandrel would do. That makes getting rings, especially silver ones, hot enough to solder on one of these quite difficult.
But there’s another option. In addition to these graphite mandrels, you can get the same type of tool – a tapered heat-resistant mandrel mounted on a holder for soldering – made of a ceramic material that’s not a good heat conductor. These make it much easier to get the ring hot enough to solder.
The graphite ones do have their uses, though. Sometimes you actually want to keep most of the ring cool. With my graphite one, I modified it with a flat surface filed onto the top, much as some grooved mandrels are made in steel, though with mine it’s just a flat facet. That section of ring over the flat is not in contact with the graphite, and it’s possible to heat it up for soldering, while the sections in good contact with the mandrel are kept cooler. With silver, of course, the heat-sinking capability of the mandrel is little bothered by the flat, since the silver so easily moves the heat past the gap anyway. But with gold, it can be pretty useful.