Hi Scott: When I lived in Dallas, I acquired some yagi elements from an
engineer who worked for Rockwell/Collins . They were welded in 4 spots
at each joint, not completely around the joint. There was no evidence of
cracking or other failure at the joints.
I also acquired some tubing elements in a Collins bid sale which had
rolled grooves at the joints. I built a tool to do this type of joint
and have used it in building a number of antennas with no apparent joint
problems. The tool consists of a medium sized tubing cutter which was
modified. The round cutting blade was replaced with one which had a
rounded edge rather than a sharp one. The new blade had a radius of
about 1/16 inch at its outer edge. I roll this tool around the joint
several times while gradually increasing the pressure (just like cutting
tubing). I usually make 2 grooves about 2 inches apart. I have used this
on some extended top whips for Hytowers which are constantly waving in
the wind. There is no evidence of cracking at the joints after 7 years
of use.
My "Machinerys Handbook" has lots of info on aluminum alloys. I
believe a lot of the stuff we find in Yagis is 6061-T6. The first 6
means it is an alloy of aluminum, magnesium and silicon. The second
digit 0 means there is no special control of impurities. The last 2
digits identify different alloys in the group. The T6 means it is
"solution heat treated then artificially aged".
I suspect a complete weld around the joints would anneal the tubing
and weaken it. I have wondered about using the special aluminum solders
frequently demonstrated at ham conventions. The guy who sells them uses
a propane or MAP torch to make beautiful repairs on material as thin as
beer cans and as thick as aluminum engine blocks. There are probably
people on TT who know a great deal more about this than I do and I hope
they will join the discussion.
73, Dan, N5AR
S Johns wrote:
>
> After having a major project at work that involved a large amount of
> aluminum welding by our fabricator, I started to wonder why I had never
> heard of hams using aluminum welding to _more securely_ fabricate large
> booms and elements (eg. 80m and 40 m full size elements for yagis and
> verticals).
>
> Other than the obvious problem when deconstruction is desired, are there
> any other downsides to welding telescoping aluminum elements?
>
> 73, Scott W3TX
>
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