"NY" wrote in message
o.uk...

When I was tightening up some bolts that used an Allen key, I started to
wonder: how do they make the hexagonal hole in the top of the bolt that the
key fits into ?

I imagine they drill a pilot hole and then enlarge it with a milling
machine, but the corners of the hexagon are angular, not rounded as you'd
expect a milling machine to make. Or do they finish it off with a very
small diameter milling tool so the corners, although still rounded, have a
very small radius or curvature and so look to be a sharp-cornered hexagon?


They will be hot stamped or rotary broached in quantity, but this is how I
did a 'one off' :


http://madmodder.net/index.php/topic...html#msg103240


Andrew