[ithacaartist]

I'm having trouble understanding why annealed drill rod, or whatever alloy, is still too stiff to form. When annealing steel, the longer it takes to cool down from cherry red to working temp., the closer it will be to dead soft. Try sticking the hot piece into a metal container of hot ashes, and allow the whole deal to cool overnight. This will act as insulation and buffer to ensure that the cooling will take as long as possible.
Also, have you considered doing the bending hot? It would be a lot easier, and if you're heating the piece to anneal, anyway, why not bend 'er when she's most plastic?

As far as the material's bending where you don't want it bent...
The points of contact opposite the internal apex of the right angle, on the outside edge of the piece, must be pretty close to the point of contact for the inside mandrel/pin, and it would help prevent the formation of a "dent" by each of these contacts if they were smooth-could even be flat. If you simply set up a square, inside corner and pushed/tapped the correct point along the length of rod straight into it with the tip of a screwdriver (Dress/grind the tip to remove the sq. corners, to the internal radius you desire.), that should do it for sure, if you're doing it hot. If cold, there will be "springback", so you'll need to make the corner more acute than dead square--this determined by how much the material of choice springs back after bending forces are removed, thus a little experimentation is necessary to determine the degree of acuteness necessary in order for the formed piece to be square after you let off bending and it springs back.

I hope this is clear. Sometimes difficult to put everyday activities and procedures into words! ...Try writing a set of instructions for tying a shoelace into a bow knot!