[TowerTalk] Aluminum tubing slip joints seized - my final answer

[Gene Fuller]

There is no "simple " answer. IT ALL DEPENDS - on bending moments, 
restraining moments, strength  of materials, loading, etc. If the larger dia 
tube is getting near it's limit you might want to extend the smaller tube 
further into the larger to accumulate restraining moment. With my LP 46 foot 
elements I have four layers of tubing near the boom. That way I keep the OD 
down to 1 5/8" but should be safe up 100 mph with 1/4 " of ice and a good 
safety factor. So far it's been fine up to 85 mph...............

----- Original Message ----- 
From: "Robert Chudek - K0RC" <robert.chudek at gmail.com>
To: <TowerTalk at contesting.com>
Sent: Wednesday, September 07, 2011 7:16 PM
Subject: Re: [TowerTalk] Aluminum tubing slip joints seized - my final 
answer


> The issue was a little more "complex" than I first thought.
>
> I discovered there wasn't a simple 4" to 6" of overlap, but about 48"
> instead. It's apparent this antenna was not assembled to manufactures
> specifications. The extra tubing did not add to the mechanical strength.
> It only added unnecessary weight. The excess tubing was at the tip end
> of the tube, not the tower end.
>
> What did work to some extent was inserting another (long) tube from the
> opposite direction and driving the inside tube toward the tip. This was
> only partially successful and I had to resort to the hacksaw. Actually,
> I used a tubing cutter for a clean cut. Then I drove the remaining
> inside piece back toward the tower end. I had to use this method on both
> halves.
>
> Pulling a few pieces from my aluminum pile I was able to reassemble the
> antenna. At the same time I added stiffening to the junctions by adding
> internal sleeves where needed.
>
> The remaining task is to model this (again) and see how to make a 62.5
> foot element resonate at 7.1 MHz. I'm thinking capacity hats somewhere
> out near the ends, like the Cushcraft 2 element 40m yagi.
>
> 73 de Bob - K0RC in MN
> ------------------------------------------------------------------------
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk