William Duffield
If you have a scroll chuck for your lathe, you might be able to chuck the bolt in it by the head, very carefully aligned, and grind the bolt to a point with an angle grinder, while the lathe is turning. That's how I taper the points on awls. Warning: Sweep up under the lathe first. Lots of sparks. If you can't get the hex head aligned in the chuck, just cut it off, then chuck the headless bolt, and when you're done, use a hacksaw to cut a screwdriver slot where the head was.

When I want to flute or reed a column, I keep the column between the lathe centers that I used when I turned it, and build a jig that holds a trim router horizontally at center height, and that slides on the lathe bed. My lathe does have an indexing head, so I can lock it to keep it from rotating at any angle I need. The only problem I've had with this arrangement is that the weight of the router want to tip the sled off the lathe bed. It helps to extend the sled beyond the far side of the lathe bed and add a counterweight.