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I'd like to make my own structure that will hold roughly 50-100lbs of equipment. Since I need this to be portable, I feel like aluminum tubing would be the most practical.

My structure will basically be a 2.5'-10' cube. I want to get 2.5' tube sections that I can connect very sleekly (word?) and make a cube that is 2.5' at its smallerst and 10' at its largest.

Taking a cue from a photography backdrop, they have 1" diameter tubing that sort of fits into itself. The tube is not flared, but it's pinched so it's the same size as the inner diameter.

Is there a name for this "pinch" I'm talking about? And if so, is there a tool I can buy to do this?

enter image description here

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Summary

The general term for changing tube and pipe diameter is swaging. The tools you are looking for exist but vary widely in price and complexity. It may be more straightforward to find a local metal supplier who can do the swaging for you based on your specifications.

Flaring vs. Swaging

I am unsure if there is a specific name for the process which is the opposite of flaring, however flaring is not quite what you are looking for. The term flaring is generally applied to the process of making the end of a tube or pipe or tube a conical shape of larger diameter than the original tube or pipe, especially for special plumbing fittings called flare fittings and is shown below. The image shown is from the link provided. The flared end of a copper tube is shown at the marker (C) in the image, while the nut marked (B) goes over the left-hand threads on the male fitting, sealing the connection.

enter image description here

The general term for continuously deforming hollow cylinders by mechanical action to change their diameters is swaging (Wikipedia). Swaging is similar to drawing and extrusion. Drawing and extrusion are terms generally applied to solid, constant-cross-section bodies such as rods, while swaging is generally applied to tube and pipe. Additionally, the swaging process is usually applied only to a portion of the length of a tube or pipe for some engineered purpose, as you are seeking.

A diagram demonstrating the process of swaging, which is done by drawing or pressing a tube or pipe through a die, is shown below. The pipe is moving from the left side to the right side of the image, through the yellow-colored die, and its outside diameter is being decreased as a result. The image is from www.felss.com.

Swaging diagram.

Options

Benchtop swaging equipment does exist, such as at this link from www.mscdirect.com , though depending on what you want to do the price may vary and end up significantly lower, such as at this link from www.directindustry.com. No affiliation or endorsements are implied with these links and they are intended for illustrative purposes only.

Another option is to find a local metal part supplier who has all of the tools and order the pieces custom-made to your specifications. The materials and labor to shape the materials will probably end up being less expensive and higher quality than with a novice DIY approach if this is a one-off or proof-of-concept. Additionally, you have experts who know how to cold work metal and may be able to provide minor additional advice.

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  • $\begingroup$ One of the best StackExchange answers I've received in a long time. Thank you for the thorough and detailed response! I think I will contact the "Metal Supermarket" in my area and see if they are able to do this. So far, they have the cheapest aluminum tubing. Thank you again! $\endgroup$ – ntgCleaner Feb 16 '16 at 1:43
  • $\begingroup$ You may want to wait a bit (usu. 24 hr) to mark mine as accepted just in case something even better comes along. I've been surprised before! That said, I hope at the very least a metal stock shop could point you in the direction of a fab shop where they can cut/shape the material for you. Best of luck! $\endgroup$ – wwarriner Feb 16 '16 at 1:45
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    $\begingroup$ if something better comes along, I'll mark it as accepted - but I doubt that will happen! Marking your answer as accepted also shows that you've given me the information that I need and I'm not looking any farther for more information. Thanks! $\endgroup$ – ntgCleaner Feb 16 '16 at 1:47
  • $\begingroup$ @ChrisJohns answer also reminded me that for most aluminum alloys, close fitting tube will eventually gall and become harder to fit together over repeated uses, while steel will not have that problem. Something else to consider. $\endgroup$ – wwarriner Feb 16 '16 at 21:45
  • $\begingroup$ @ntgCleaner I think Metal Supermarket is more of a metal supplier than a fabricator $\endgroup$ – ikrase Apr 19 at 21:44
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For a one-off structure swaging or flaring tube is probably a bit of a long way round to do it. There are actually quite a few off the shelf solutions for joining tube, an example at random

Something else to consider is that, for something which is disassembled and moved about a lot, if your system relies on one tube fitting inside another then and damage to the ends of the tube will mean that they no longer fit properly and the method of fit will have significant effect on the stiffness of the whole structure. With this in mind any system which either puts a permanent rigid insert in the end of the tube or clamps on the outside is likely to be preferable in terms of both durability and stiffness.

It is also worth saying that any operation which involves ductile forming of metals tends to be a bit fiddly as the parameters depend a lot on the precise material properties of the raw materials which can vary a bit from batch to batch.

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  • $\begingroup$ You make a great point about connectors. Those connectors are pretty awesome too (the random example). I'll have to find someone who has straight connectors (All of theirs seem to be angles, plus they're out of the UK). I'll take a look around. Thank you! $\endgroup$ – ntgCleaner Feb 17 '16 at 2:09
  • $\begingroup$ Also, great information on the fact that the tolerances are different depending on the batch of metal. In your opinion (or maybe even experience) do you think 4 bars, linked with connectors could hold between 30-50 lbs? $\endgroup$ – ntgCleaner Feb 17 '16 at 18:14
  • $\begingroup$ Obviously much depends on the detail but 50 lbs supported by a 10' cube certainly seems plausible with this sort of system. $\endgroup$ – Chris Johns Feb 17 '16 at 21:06
  • $\begingroup$ Thank you, I might need to clarify - the 50 lbs will be supported by a single 10' section consisting of 4 x 2.5' tubes and 3 connectors. I was able to support it with 1" tubing in the same fashion, but it was definitely precarious. I did not feel comfortable doing that again. $\endgroup$ – ntgCleaner Feb 17 '16 at 21:51

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