I’m not sure what this thread is about, but I have always made my own
rotary burnishers - we call them “hammers”, for rubbing out porosity,
mostly. It’s easy: Get an old bur (hard steel, not a “mandrel”), put
it in a vise, heat it up to red hot, and with some big pliers bend it
gently at the tip (maybe 3/8" back) into an arc of 30 or 45 degrees.
Quench it, and then grind a flat face on the tip in about a parallel
line with the shaft, and round off the edges. Then polish it, and you
have a burnisher. I have one that is the full size of the shaft, and
another that’s tiny, from a small burr - about a 1.5mm face on it.