He said shaft, not butt?
I've steamed dings out of a number of people's cue shafts. After steaming, clean with whatever you would normally use and that will go a long way toward blending in the repair. After it is certainly dry, like maybe the next day, carefully/lightly sand any raised grain starting with a touch of 500 or 600 grit, finish with 800 or 1000 at this point. Just touch & *faintly* blend it, don't over do it. This is where it's an advantage to have the shaft turning. I then use acrylic cue sealer, (Think it was from Hightower cues, but it's been a few years) which can slightly raise the grain again. Next day, burnish with 1200 or 1500; polish with a brown paper bag.
If the ding is in the area that was varnished, fresh cut super-blonde shellac made from flakes is a wonderful, fast, cure-all. Though i guess that is another skill set. Super glue as mentioned will work for some finishes, you have to be good at leveling it.
PS, depending on your skill set, all of the above can be done without the shaft turning. If you take so much material off any place that it affects the geometry of the shaft, you are doing it wrong anyway.

A lathe just makes it easier and helps prevent dropping the shaft while working it.
smt