Just for the hell of it, I looked around the garage
and spied a few scrap pieces of 1/2" & 5/8" 6061 aluminum,
so did a crude experiment.
In a large vise I clamped a short piece of 5/8" tube,
vertically. This is my concrete base.
I slipped a piece of 1/2" tube into the base, letting it
slide down till it hit the vise. 34" of 1/2" tube remained
above the base.
With a spring loaded scale I pulled horizontally on
various sections of the tube. The limit (at the point
of permanent deformity) was reached at around 12 lbs
at the tip, and 25 lbs in the middle (17" up).
Then I guyed the "mast" (a new piece of tube) at the top
in one direction. The guy formed a 45º angle with the mast,
and was snugged about "so" tight. Here the experiment is
not very scientific at all - only one guy, contributing very
little to downward force until a load is applied. But I
wanted to see the trend.
It was obvious that the weak spot is now in the middle
of the mast, where a 50 lb. load was looking like it
was close to going past the point of no return.
At the tip, it's no contest at all - the mast handled
100 lbs with no sign of distress.
By my seat of the pants figuring, the pre-tension for
a sensible guy system for this mast would contribute
30 lbs or so of downward force (if one were trying
for 100 lbs of load capability at the top).
I'm not surprised at all by this result. In terms
of diameter/height ratio, it's similar to a 12" tube
70' high. If I spy some other materials this week
I'll try another little test.
Steve K8LX
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