How can I stabilize concentric tubes with an irregular cross section?

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SUMMARY

This discussion addresses the stabilization of concentric tubes with irregular cross sections, particularly in applications where aesthetic stability is crucial. The user has experimented with various materials such as Teflon, cork, and PTFE but faced issues with friction and adhesion failure. A proposed solution involves machining grooves into the inner surfaces of the tubes to accommodate silicone or similar caulking materials. Additionally, the use of flexible spring steel or phosphor-bronze strips, akin to those found in telescoping antennas, is suggested to maintain alignment and stability.

PREREQUISITES
  • Understanding of concentric tube design principles
  • Familiarity with machining techniques for creating grooves
  • Knowledge of materials such as silicone and PTFE
  • Experience with mechanical stability solutions in engineering
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  • Research machining techniques for creating grooves in irregular cross sections
  • Explore the properties and applications of silicone caulking materials
  • Investigate the design and functionality of telescoping antennas
  • Study the use of flexible spring steel in mechanical applications
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Mechanical engineers, product designers, and anyone involved in the design and stabilization of concentric tube systems will benefit from this discussion.

charanth182
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Hi everyone,

I'm new to this site, so if I'm breaking any rules let me know. In particular because this is for my job. The forum rules seem very clear on the guidelines for homework for school and one can assume that personal hobbyist type questions aren't an issue but i don't see anything when it comes to work related queries.

I've run into a problem in which i have a few (3) concentric tubes with an irregular cross section (though the same as each other). Due to machining tolerances we're stuck with a small gap, mechanically it doesn't matter but perspective isn't so good as someone can easily shake the central tube making it look unstable.

I've tried finding a material to fit into the gap (Teflon, cork, PTFE, various tapes, cabinet bumpers etc.) but every item I've tried either creates too much friction or will not endure the movement of the tubes (often the adhesion gives).

I feel that i must not be alone in this problem as there is so many items out there with concentric tubing. How do they solve the problem?
 
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From your wording, I assume that this is a telescoping device. O-rings would work if the tubes were cylindrical, so I'm wondering if you could machine grooves into the inner surfaces of the tubes and lay in beads of silicone or or similar caulking material. You mentioned that your adhesives failed, so maybe having the material physically restrained would help.
Just a basic thought.
 
If this is a telescoping type arrangement, and if the intent is for stability--not just to fill the gap for aesthetics or a seal of some sort--you might consider a method similar to most telescoping antennas like on a basic shortwave radio or such. In between sections there is a ring fastened to end of each inside section, and from this ring radiate 3 or 4 flat pieces of flexible spring steel or phospher-bronze. These slightly curved pieces of metal wedge in the narrow gap between the walls of each section and the next outermost section, and although they slide easily the tension of these slightly curved 'springs' hold everything in alignment. I'm sure I'm not explaining it well, but if you take apart any old telescoping antenna such as TV 'rabbit ears' you will quickly see what I'm referring to. Just a thought...