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| There was such a thing reported in a 1908 or so Model Engineer magazine.
Basically the drill bit was triangular cutting on the end and the sides. Each face of the triangle was the width of the flat on the square hole. It required a guide plate with a square hole. That guide plate was to be case hardened. The drill bit has to wobble, so it pivots on a corner in the corner of the guide plate. I've not yet built a set. Or one.
The broach is the most machinist like, the big hole squaring out the corners with a little mill might be taken a notch further with a second or third smaller but, or just on one approach to the corner run the small mill till its center reaches the line its cutting past. You only need to do that four times, not 8. Its the way electronic enclosures to hold square cornered PC boards are often milled out of a solid block.
Pushing the square tool bit through might work.
It is possible to make a broach. Start with square stock the size you want, turn a taper from the full square to the round pilot size. Then cut teeth at intervals with proper cleararance. Harden it, having made it from a water, air, or oil hardening stock. And push. You probably want to take only a mill or two per tooth.
Then there's the square file sometimes known by other names. Hard to find in some sizes lately.
The socket scrap welded on solves several problems. Or if you cut a hex or welded a bolt to your plug you could pin a socket to the resulting hex.
For my little lathe, I used an expanding concrete anchor to fit the hollow spindle for cutting very coarse threads up to a stop. 1/4" pitch. Didn't work out well because the internal cutter wouldn't get closer than half the width of the cutter to the end. I suppose I should have cut a groove first.
Gerald J. | |
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Lathe play (pics)
