Turning Wood For The Mangled Headstock
If your headstock looks like this, it's probably an indication that something's gone wrong along the way.
The previous owner of this bass had left the current owner with some very badly fitting tuners. There was a heap of wood gouged out to try fit some locating keys on a set of tuners and the shaft holes had been badly enlarged and were weird egg shapes (as well as being a poor fit for the tuner bushings).
After I'd trued up the shaft holes, they were far too big. The solution was to turn down a square-cut piece of maple in a lathe until it was a nice, snug fit for my round hole.
That's how you fit a square peg in a round hole.