Up here we call them poor mans mandrels. What we do is fill the tube that is going to be bent with sand (usually left over old dirty sand blasting media) and cap the ends. It stops the tube from collapsing, and because you only tack the caps on, some sand will escape so you don't over pressure the tubing.

Nice Idea...That was a new one to me. I was having the same crumpling problem with light gage tubing I'm using to make a break-down sun shelter and camping table for the beach. <img src="/forums/images/graemlins/cheers.gif" alt="" />

for all the tricks I've learnt here, I'm glad someone learnt one from me. Now I have to come up with 2000000000002 more tips <img src="/forums/images/graemlins/smile.gif" alt="" />

It does not matter how anyone slices it, if you use pipe for a "cage" it could be the last mistake you make.
Tacked? Who cares if you are dead. Sorry if I get blunt, I just see the same questions over and over...and for years I have responded with "don't do it because..." Yet the same questions keep coming back. Why be cheap when it comes to protecting your bean or your families beans. Buy, rent or steal a "tubing bender" copy a known quality design (don't get cute) and have someone burn it together who really honestly knows what they are doing. If they show up with a 110V welder, tell them no thanks. Pipe is measured by ID (inside diameter) Tube is OD.
If you put tube into a pipe bender die, nothing will keep it from kinking. If you use pipe in a pipe bender use your bent pipe for piping not cages. You wonder why our insurance rates keep going up and why lawmakers keep trying to pass lift laws and tire size laws.

SD

I'm not sure how we got to talking about cages, since my original question had only to do with bender types. I guess a anyone with a bender will *eventually* get asked to help build a cage. Still, I really appreciate the input.

I know the difference between pipe and tubing, and I always had tubing in mind. The bottle-jack-style looks nice 'cause it's portable, and that particular company has built-it-yourself plans. The JD2 bender looks way nicer, but I don't have a place to bolt it down. (I suppose I could unbolt it when the jobs are done.)

I'll be thinking about it.

If you are going to be bending 1" tube and smaller to build racks look into a good Imperial hand bender. From 1"x.065 and smaller they are fine and pull a nice clean bend. It will be a separate bender for each diameter of tube.
You have no need to invest more until you start bending over that size.