This is the mandrel bender we use for the bending of 10 x 0.5 mm tubing with a 25 mm radius.
The main pivot is a bracketaxle, and the assembly is rotated with a large spanner on the central hexagon.
The large 120mm disk is grooved to accept a adjustable slider which works as a angle stop

The tube is clamped to the mandrel, and a shoe runs along the outside of the tube being bent to keep it round. A large bearing keeps it pressed in place.
To prevent kinks on the inside a tight fitting rod, extending just to the point where bending takes place, is essential. Just on the left you can see an endstop (not being used)  in place.

Instead of working out the necessary angle with springback, for a single bend it is usually sufficient to calculate the theoretical lenght needed for the bend, and to measure the distance the tube slides up the interior rod.

this one is for 14 x 0.8mm cromo, r=40mm

This one bends 1"x 1/16". It was used to put the bend in the Radical chainstays. The stop on the pullingchain fixes the angle.
The bicycle crank had to be lenghtened because we're weaklings, or maybe it was the cromo tubing ;) 
 

Detail of the actual bender. The tubing is clamped to the mandrel. This has to be really tight otherwise the tubing will slip and kink. The shoe is pressed against the tubing with an adjustable roller.
BTW al machined parts including the shoe were made on the lathe below!
 

This shows the rotating toolbit used to machine a proper circular groove