I take 1" steel spacers, true em up on the lathe, taper one end down to .840, insert a threaded delrin or phenolic plug, then finish away. I let the finish get up and over the mandrel, then I sand it down. Once the finish is complete and dry, I take it off the lathe, then lightly tap the mandrel with a bronze hammer, and a quick twist cleanly breaks it free from the clearcoat on the minutia of face showing on the mandrel. Also, a little wipe of wd40 on the mandrel seems to really help.
I seem to be able to get a few finishes and sanding cycles out of one before it gets smaller than .840 and I make a new one.
It's not as accurate as a carbide mandrel I suppose, and it doesn't last forever, but it only takes me 5minutes to make one and it costs $1.50 each time I make one.
Works good for maintenance arbors too.