Here is a pic of the collet we made for the push bending. We made the collet from 17-4 PH H900 material. It is the same material we make our hubs and axles from. It is ridiculously strong. I love the stuff because it is a PH or precipitation hardening material. PH means that in order to harden the material, I only need to heat it up to 900 degrees. Other materials, like chromoly have to be heated up to 1525 F and then quenched to get hard. The quenching process is hell on the material. Any stress raisers will cause the material to crack from the quenching shock. 17-4 is really expensive (about 5 times more expensive than chromoly) but you don't have to worry about losing a part in heat treat from a stress crack so it is worth it to us. Not to mention, 17-4 eliminates micro cracks which scare me to death. Some things are just better to use the good stuff on. There are better materials, of course, but cost becomes prohibitive.
In the previous picture, it is a little hard to tell, but you can see the 2 inch collet in the end of the push ram. It has the mandrel sticking through it. It is the piece with all the little holes in it that is cut into 4 segments. I cut this collet apart in the next pictures.
