Just read this excellent advice after attempting this braze-sanding thing for the first time as a total rank amateur and using a dynafile
Below is a mercifully slightly out-of-focus picture. These are actually cosmetic TIG brazes over the top of TIG welds (that I have a lot of confidence in). The upper segments are made of offcuts from the steerer tube and are 2.4mm wall CroMo. The fork blades are 0.9mm CrMo. I was very careful to only touch the bronze bits with the sander except for the very last bit of blending at the edges. I found it helps to use the bit of the belt that doesn't have a platen under it and to hold the edge that you're blending with the steel side towards you. The fork isn't finished yet-- it needs the crown race seat and some cantilever bosses (which I think I'll just TIG weld).
TIG welded and brazed fork