Tube Bending

The classic problem with bending tube is getting a "squish" in it.  This
results from the tube colapsing and folding, rather than bending.  One trick
i have seen described calls for filling the tube with sand before bending.
Since the tube cannot collapse onto the sand, since the sand fills it, it
cannot squish.  Getting the sand OUT later is another problem, especially if
a longish spiral is involved.

Another approach is to try to support the "sides" of the tube while bending.
(Look at an electricians conduit bender.  Same principal.  The "sides" are
restrained by deeep flanges.  Since they cannot go "sideways" the squish does
not develop.  I visualize something like two pieces of plywood, spaced the
tube diameter apart, held together with bolts (to allow disassembly when done),
This would need a "spacer, flexible, to go between the turns...  (I am
brainstorming, here...)

I wonder if a liquid (noncompressible) filling, TIGHT end caps, would do the
trick.  Seems it ought to but both ends MUST BE TIGHT.  Even if the end few
inches were used for sealing and discarded later.
(hmmmm.  run coolant thru the coil, with insulating fittings, while in
operation...  nahhhh...  (Near here is one end of +/- 500KVDC link.  They cool
the SCRs with an exotic insulating liquid: ultrapure water.  Yes.  pumped
live thru the system in electrically insulated plumbing....))