I know an individual who is seeking a source for telescoping hex tubing
each piece of which is something like 30" long, made of low-carbon steel (the
material isn't that important, but it doesn't need to be stainless or unusually
tough or hard) in dimensions like 2" OD, far larger than anything he has been
able to find commercially.
He is now considering fabricating jigs to hold flat pieces to be brazed into
30" sections. He is also willing to consider welding.
Does anyone have any idea how to make this stuff? Six sided stock would have
six joints to braze, and it would seem difficult to braze them all at once.
Welding would be tough because the material would tend to move and because
there might be "drip-through" into the interior which would make any
He wants to pay me to make him a jig, and I am leery of getting involved.
Why don't you make a mandrel and roll flats onto standard steel tube? I
think you could find suitable tube in graduated sizes. I think after
the rolling, that
the tube would spring back enough that the mandrel could slide out easily.
How about aluminium ? Extrusion seems an obvious possibility.
To make steel tube, I'd use a press brake to press the six folds in,
then seam weld down the middle of a flat side. If it has to be smooth
enough to nest, then I'd talk to some commercial setup with a
resistance wheel welder (like continuous spot welding)
Klein bottle for rent. Apply within.
Grant Erwin wrote: I know an individual who is seeking a source for
telescoping hex tubing
I'm not saying this is the best way, but I know it could be done. Start
with a piece of solid hex stock which will be the mandrel for the first
piece of tubing. Cut steel strips wide enough to form the six sides, and
hold them in place around the solid hex with hoseclamps (for starters).
Weld the seams using an oxy/acetylene torch and NO filler rod. You can get
very smooth welds this way with little or no penetration to the inside. Now
use the newly made hex tube as a mandrel for the next one, and so on.
It may turn out that you need shim stock between the layers to allow them
to slide apart. You would have to try it to see. It may turn out that you
have to grind a bevel on the edges of the strips to reduce the 60 degree V
gap. With the 60 degree edge-to-edge angular gap, it could turn out that
silver solder or brazing, carefully done, would produce a smooth joint.
Taking Andy Dingley's idea of using a brake, and combining it with mine, it
might be possible to form the tubes with five bends and one weld at a
corner--or a braze at a corner. Or maybe forming the tube in two halves,
and having two welded or brazed corners.
This is a very interesting challenge--it seems a little experimentation
would be in order before you bid the job.
Forming the hex tubing from standard tube or pipe was the
first thing that occurred to me, too, but rather than
forming flats over a mandrel, I envisioned explosive forming
of each length inside the next larger. :)
Explosive forming no, hydro forming yes. Rolling no: you can't
get a hex mandrel in a round tube and still have it work. You
can't roll it free form because you can't get a flat side. You
might be able to roll it in a 6 sided turks head roller (if the
made such a critter!)
If you HAVE to make one, press brake 2 bends in each of two
clamshells, TIG weld in automatic or manual fixture. You are
still going to have a LONG day getting the telsescoping action to
James Waldby wrote:
Good morning Grant,
After reading the other responses and warming up the gray matter (what
little there is), a solution comes to mind. Because these are fairly
short compared to the diameter maybe the tubes could be pushed into a
die with a hex mandrel inside. You didn't say what the wall thickness
needs to be. But forming this way would only be good for lots of
pieces. Hydro forming seems like it would be cheapest for small runs.
The hex dimension would depend on what was available in round and it
may be that the different sizes of round available, when formed into a
hex, will not nest correctly. And for just a very few, using a brake
to form two halves that were welded together woulkd be the best
(cheapest). Has this fellow tried Kislby Tube Supply?
Hydroforming is great, if you already have the equipment. Otherwise,
it is certainly not the choice for a short run of one part.
I still thing rolling on mandrels would work, but it might take several
graduated mandrels to arrive at final size and shape. That makes it
more complex, of course.
Jon Elson wrote: (clip) I still thing rolling on mandrels would work, (clip)
I am puzzling over this. A hex with 1" sides would have a 6" perimeter. If
you start with a round tube with a 6" circumference, it will have a diameter
of 1.9". The mandrel will have a corner to corner measurement of 2". How
will you get started?
I suppose you could grind the mandrel round at one end, and force it in. Is
that what you had in mind, or am I missing something?
No, I was thinking about starting with oversize tube and squeezing it
onto the mandrel.
If this worked, it could be done with pretty simple shop equipment.
The force required to slide the desired tube diameter over a tapered
like a lot, although with the right equipment it might be a good way to
I really don't know the quantity of these the original poster was
needing. I think he
wants just a couple of pieces first for a proof of concept. Obviously,
there are several
production processes that could make these parts very nicely,
one of the most promising.
The plant beside the one I work in does hydroforming. NOT a cheap process.
1800 ton press to close the die, something like 60ksi hydraulic pressure
within the tube itself. I'm sure time on that thing is big money, not to
mention the tooling. Forming time is something like 35 sec per part.
Perhaps using a female die (like hydroforming) with a neoprene male punch
instead of hydraulic fluid. I wonder how one does tonnage calculations for
such a process.
sounds like another good job for primacord.
"Aren't cats Libertarian? They just want to be left alone.
I think our dog is a Democrat, as he is always looking for a handout"
Unknown Usnet Poster
Heh, heh, I'm pretty sure my dog is a liberal - he has no balls.
Possible search terms: "Marform" or "Hidraw". They mention both
aluminum and steel deep drawing. It's not very detailed on this
subject compared to all the information on conventional dies.
Book is _Die Design Handbook_ 3rd Edition, Smith
published by the SME.
Make an inside holder from copper plate - the
steel weld won't stick to copper and the
copper will form the welds nicely.. So, in
effect, you'd make a hex tube of copper plate,
where you place the steel plates on top of the
copper, and then weld the six seams. Propably
easiest to make the inside holder from steel
hex with thin copper foil wrap.. As well, use
flat holder bars on all plates, bars connected
to inside holder (each hex flat) with bolts
Still - why on earth hex.. Why not normal
Thanks to all for their great ideas. My contact is an inventor who does
not wish to discuss why he wants to use hex tubing. I have solved his problem
by locating him a vendor who stocks steel hex tubing. In case anyone else is
looking for stock hex tubing, he found his at
Perhaps I'm missing something. Tubular hydroforming is not really deep
drawing. It's a fairly mild draw, I believe.
I've got the same one. I'll have to take a look. (most expensive text I've