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Tubing Test:

Posted by pictureguy (A) on November 2, 2021 at 21:42:24

In Reply to: Material for new frame posted by SteveJewels on October 31, 2021 at 17:02:06:

Many people like 'mass loading' of tubes.

I start with the idea that wall thickness to Prevent what's called a 'soda straw' break should be at some minimum. Maybe 1/50 the diameter? Something along those lines. So for a bicycle wher you need a certain amount of rigidity to, just as a goal, MIMIC a decent mild steel tubing you need a greater diameter of aluminum.....In this case a 6061 alloy is Very common. This drives wall thickness, up, too. The result? While Aluminum weighs about 1/3 LESS than steel, the net savings for an equivelent aluminum structure is MUCH less. I've seen this with aluminim wheels for big rigs and aluminum trailers, also for big rigs. You DO save some weight but not 1/3. And also? You must deal with fatigue limits, which should NOT BE the case with a frame for Panel Speakers where it is never stressed anywhere NEAR its tensile limits.

Instead, I'd like to propose a means to increase RIGIDITY of a tube And a way to TEST, using materials you can easily get at a hardware store.

You'll need some 2" diameter PVC, schedule 40. You'll need CAPS for the ends and an EYEBOLT to go thru the pipe from which you can hand a weight. A straight edge and a 6" scale calibrated in 64s or better. And finally? EXPANDING FOAM.

The first test? Simply cap off a 3 foot length of PVC and weigh it down with a 10lb weight. MIght take MORE but not likely LESS to produce a measurable deflection. Hang the weighty from the HOOK in the middle. Than REPEAT with cured (let it sit for a day or so) expanding foam. this will test just how much MORE rigid the tube is. Use the same weight and means of measurement of deflection.

It might be possible to repeat again but using some kind of 'fill' mixed in with the expanding foam. Maybe some kind of steel shot. DO NOT USE LEAD. It is toxic and whoever inherits the frames will have NO IDEA what is in 'em......This would require some experiment to get the 'mix' right but will add mass and rigidity to the extent everthing 'sticks'....

It is possible that the PVC may not stick properly to the expanding foam. Than it'll get odd. An ACETONE wash to remove the mold release will fix this, I think. I glue PVC without 'primer' by that method and have never had a joint failure.

If this is successful, the technique could be applied to any tube.....

If this works, and I'm fairly certain it WILL, the technique could be applied to other layered materials. Which could than be cut to shape for frames or even speaker stands.....

Too much is never enough

This post is made possible by the generous support of people like you and our sponsors:

Atma-Sphere Music Systems, Inc.

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