telescoping hex tubing

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
telescoping difficult.
He wants to pay me to make him a jig, and I am leery of getting involved.
Comments?
Grant Erwin
Kirkland, Washington
Reply to
Grant Erwin
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Why don't you make a mandrel and roll flats onto standard steel tube? I would 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.
Jon
Reply to
Jon Elson
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.
Reply to
Andy Dingley
Oh, oh! OT question from the peanut gallery: Why hex?
Regards,
Robin
Reply to
Robin S.
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.
Reply to
Leo Lichtman
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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. :) -jiw
Reply to
James Waldby
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 work smoothly.
James Waldby wrote:
Reply to
Roy J
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? Cheers, Eric
Reply to
Eric R Snow
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
Reply to
Jon Elson
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?
Reply to
Leo Lichtman
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 mandrel sounds like a lot, although with the right equipment it might be a good way to make the part.
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, hydroforming being one of the most promising.
Jon
Reply to
Jon Elson
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.
Regards,
Robin
Reply to
Robin S.
According to my die book, 5,000 to 15,000 PSI, with 6,000 being common.
Best regards, Spehro Pefhany
Reply to
Spehro Pefhany
Does that range cover mild steels or all metals or...? Which book are you looking at (just out of curiosity..?)
Regards,
Robin
Reply to
Robin S.
sounds like another good job for primacord.
Gunner
"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. Keyton
Reply to
Gunner
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.
Best regards, Spehro Pefhany
Reply to
Spehro Pefhany
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 at ends..
Still - why on earth hex.. Why not normal rectangular tubing..
Kristian Ukkonen.
Reply to
Kristian Ukkonen
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
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- go have a look! - GWE
Kristian Ukk> Grant Erw>
Reply to
Grant Erwin
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 ever purchased)
Regards,
Robin
Reply to
Robin S.

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