I called JBWeld for household mold release, and they suggested either WD-40 or Vaseline (petroleum jelly). I have WD-40 in the garage, so I tried it on a scrap bolt and scrap wood.
It worked, well, maybe. I waited an hour or so for the 5 minute epoxy to cure, and it seemed hard. When I tried to unscrew the bolt, it came out easily, but bits of soft epoxy thread broke off and fell out with it. They were soft and sticky; not fully cured. Still, I took the message to mean: WD-40 prevents epoxy from sticking.
I had a scrap of leftover mahogany to use up, and it was the right thickness. I drilled the piece, used a Harbor Freight hole saw to cut out the knob, sprayed the handle with WD-40, and glued the "knob" on with West System G-Flex epoxy. I used a ratchet clamp to press the knob on, and the wood failed - leaking epoxy out of a crack or hole in the side of the knob. The wood was kinda' punky anyway; it was my fault.
I pulled the knob off, and the syrupy epoxy cleaned right off. The WD-40 on the handle made it easy. Another confirmation that the WD-40 would work.
I found a solid piece of maple. It was not as thick as the metal knob, but close enough. I repeated the hole saw, drill, WD-40, epoxy, clamp, and cure ... and everything held up fine.
-> Once the epoxy cured, I could not unscrew the knob by hand, nor by hand with heavy leather gloves. There was plenty of WD-40 on the handle, but the epoxy is gripping very well. (I could have used tools, but did not want to chew up the knob.)
I gave up on having a wood knob that unscrews - there is an original metal knob on the other end anyway. (If I must, I can chisel off the wood knob; hopefully the epoxy will clean off.)
I mounted the handle on the lathe, sticking out of the chuck, with my rough wood knob on the end. I shaped the knob with turning tools. I sanded it with the usual turner's sanding strips to 600 grit. I finished it with Hut Crystal Coat. I am not that fond of Hut Crystal Coat, but it was fast and easy, and I look for excuses to use it up.
I tested the handle by allowing it to drop vertically from the metal end to the wood end in the vise, the way it would in normal use. It works well.
* After curing, West Systems G-Flex would not release the metal handle even though the handle was well-coated with WD-40.
* I never tried Vaseline (petroleum jelly) - it might have worked better (??).
* I spent way too much time on this project.
Photo: Vise Handle with Turned Wood Replacement Knob