Here is the other side of the collet. The part is pretty precise to make sure everything has the right gripping power--not too tight to crush the tube and not too loose so you can't control the tube as you move it around and index it for the next bend. Those holes are only 0.1875 in diameter and they are almost 4 inches deep!
Drilling all those holes made me SWEAT bullets. We have a special mill set up with a special cutting
oil (not a water based coolant) for our really nasty milling operations (like our hubs). It makes a MESS; but, it makes nice parts
and no broken drill bits after almost 48 inches of drilling through nasty stainless.
Now granted, stainless is not the material of choice for most bending operations. It only gets to about 45 Rockwell C. But for as little bending as we do (we aren't making 1,000,000 parts like some guys do) so we don't need the Rockwell 55-60 stuff. That stuff is a real pain in the butt to machine, heat treat, and hold tolerance with. You end up having to send it out for heat treat and grinding and that just ends up eating up your life in waiting for sub-contractors. We do our own PH hardening in house (and some quench hardening when it is forced upon us--but I try to avoid that like a politician telling the truth).
