I've been trying to make a winding key for a clock I have--the winding shaft is about .140 inch square, so I need a hole about that size. The way I have tried to do it is: in a 5/16 steel round rod, I predrilled one end in the lathe, using a drill about .140 diameter. I prepared a square key with a bit of taper. Then heated about 1 inch of the predrilled shaft to red, maybe orange (it cools quick) and hammered the key into the hole. It took a couple of heats. Result was a square hole, but the shaft bent a bit, so when I tried to turn the shaft afterward to clean it up (I want a smaller diameter), the hole was off center, and I could not clean it up properly.
Tried again, this time holding the key in a vise, and hammering the shaft. Same result.
How is this done? Commercial keys are nice and slender, and the hole is nice and neat.