Mechanical Tubing Connectors 1

[stunju]

I have been given the task of taking one of our machines (10foot long) and making it packable (5 foot sections). The design problem is the 10 foot long mechanical tubing square and round, steel and aluminum. I am wanting to cut the tubes and the reconnect them. We cannot use internal threads (that would be too easy!) I am trying an insert in the pipes that will use a cam lock style connector to draw the tube ends together and compress them to create a strong joint. This way I only have to drill holes in the tubes and insert the cam (like cheap furniture). Any ideas? Anybody know of any cam lock manufacturers?

 

[Cheddarcaveman]

What size (OD/ID) are the tubes you want to cut/join?

 

[Cheddarcaveman]

Further to my last, also what pressures are you using? Have you thought about standard plumbing compression fittings? No mucking about, just insert the pipe ends into the fittings and tighten! You do need a nice clean OD on the tubes as there is a compression ferrule that has to be a good fit onto it.

 

[stunju]

I am sorry cheddarcaveman. The application is not pressure rated. The tubes are structural elements. They are laid out horizontally and loaded with point loads and distributed loads. I cant have any external to the tube walls connectors. It all must be within the tubes. For clarity lets talk about a 35mm OD 5mm wall 6061T6 aluminum round tube. Now lets cut it and connect it. How?

 

[MikeHalloran]

If you have access through one end of the tube, the simplest connection is a screwed wedge, as typically used to retain the handlebar stem inside the fork stem of a bicycle.

Based on your description, I'm guessing that there are both tension and moment loads on the assembled joints, and that something has to slide over them, so misalignment and looseness would not be acceptable.

If that's true, I'd lean toward something with spring pins that pop out into drilled holes in the tubes, and a screw- jacked draw wedge to pull the tube ends together.



Mike Halloran
Pembroke Pines, FL, USA

 

[marmon]

I assume the square tubes have a welded seam? That makes things very difficult, hence your question. Anyways can you start with new tubes? so you can machine a step on one end to slide inside the other then maybe with a redi-rod fixed to one half, and slid all the way through the other half, with a nut to draw it up tight? kind of hokey but??

 

[stunju]

I am now looking at cam and dowel connectors like used in self assembly furniture I don't know if I can modify the design to accept larger draw forces. Anybody know?

 

[MikeHalloran]

I think you'll have to figure that one out for yourself, because we don't know all the requirements.

The typical furniture cams have a pressure angle such that they're just barely self-locking in wood, and don't produce a lot of draw force for the torque applied. Don't be sucked into just scaling up the geometry of someone else's design for a different problem, building it, and testing it 'to see if it works'.

Instead, analyze how it works, yes with numbers, adapt that math model to work your particular problem, optimize it, and then generate the geometry you need from the numbers.



Mike Halloran
Pembroke Pines, FL, USA

 

[stunju]

Mike, I appreciate your input. When I get back to the States I plan to begin tests with the furniture cams to see what I can get with off the shelf components. But, I expect to be making a custom part before it is all over with. I am in China currently and my internet searching capability is limited by govt filtering and bandwidth. Any suggestions of manufacturers would be appreciated.

Stu

 

[MikeHalloran]

Try selbyhardware.com. They seem to have a wide selection.


Mike Halloran
Pembroke Pines, FL, USA

 

[prephil]

try banjo.com