Best Practices for Not Crushing Thin-Wall Tubing

[Chris is me]

Originally Posted by JamesCH95

Why did you feel that this was necessary?

Some quick bearing load calculations assuming 1/32in wall, 3/8dia dead axle, and passing it through two tubes (thus 4 walls), and a 35ksi yield strength: 1/32in x 3/8in x 4 x 35,000psi YS = 1640lbf of bearing strength through just the walls of the tubes.

I would definitely be concerned about creep more than pure yielding. We had all kinds of creep failures when we mounted screws directly to VersaTubing last year without gussets or other material support.

That said, might be easier to just make a gusset plate and slap it on the outside?

[Oblarg]

Originally Posted by Chris is me

That said, might be easier to just make a gusset plate and slap it on the outside?

We did this with our catapult last year - we used slices of C-channel to support the steel bar that our pneumatic pistons attached to, since we were afraid the thin-wall tubing would not hold up so well after repeated shots.

[JamesCH95]

Originally Posted by Chris is me

I would definitely be concerned about creep more than pure yielding. We had all kinds of creep failures when we mounted screws directly to VersaTubing last year without gussets or other material support.

That said, might be easier to just make a gusset plate and slap it on the outside?

Why do you think it was creep? My understanding is that creep typically takes many hours, or days, to manifest.

I'd think a plate on the outside of the tube would be a lot easier and probably lighter than an insert, too.

[Chris is me]

Originally Posted by JamesCH95

Why do you think it was creep? My understanding is that creep typically takes many hours, or days, to manifest.

I'd think a plate on the outside of the tube would be a lot easier and probably lighter than an insert, too.

Creep is the wrong word, I think. What I meant is that wear on the hole from vibration or cyclic loading of the bolted part happens much more quickly on .04 wall tube than any other size. This kind of wear is something that I've been able to ignore elsewhere in FRC due to the short life span, but in this tubing you can't. We added some plates to increase the effective material thickness at the hole site and riveted the plate to the nearest neighboring holes.

[JamesCH95]

Originally Posted by Chris is me

Creep is the wrong word, I think. What I meant is that wear on the hole from vibration or cyclic loading of the bolted part happens much more quickly on .04 wall tube than any other size. This kind of wear is something that I've been able to ignore elsewhere in FRC due to the short life span, but in this tubing you can't. We added some plates to increase the effective material thickness at the hole site and riveted the plate to the nearest neighboring holes.

Rodger that, makes more sense than creep!