Q: I seem to have scratched up the point of my tungsten carbide burnisher, probably by rubbing it on a diamond or something. How can I repolish it?
A: You need diamond compound. Ideally, you’d either have a proper lapidary setup with diamond polishing wheels, or something like a GRS Powerhone with its diamond grinding wheels for shaping, and a ceramic wheel with diamond compound for polishing.
Barring that, you can make a small wooden wheel for use on the flex shaft that works very well, but slower. Cut an eighth-inch long slice of a one inch wood dowel, and drill a hole in the center so you can mount it on a standard mandrel such as you’d use for rubber wheels. True it up so it spins flat and true, then, if you like, carve into one surface slightly with a bur as it spins so it’s got a slightly concave flat surface on one face. Put a tiny dab of 14 thousand grit diamond paste compound on that surface, and polish away. The concave surface somewhat better fits the slightly curved bullet shape of the burnisher point, and reduces the speed at which the compound is thrown off. The wheel gets better as you use it, and needs recharging only rarely. If you want an even higher polish, make another one for fifty thousand grit compound. Initial shaping can be done with a small 600 grit diamond wheel. Crystalite makes a number of them that will mount in a flex shaft. Use them with oil or water, not dry.
An alternative that’s simpler are the German- made diamond-charged rubber wheels that are marketed for use with platinum in particular. The green medium grit ones will leave a fine scratched finish, roughly like a 1200 grit wheel, the grey grade will take that to a reasonable polish, and the pink ones take that to a high polish. The downside to these wheels are their cost, and their small size which makes it harder to get a nice smooth finish on the burnisher instead of a slightly wobbly or faceted finish. But they do work well to polish the carbide, and at high speeds, are just killer on platinum.