[TowerTalk] Subject: Wind survival + load ratings... vs,

[Jim Thomson]

Date: Thu, 2 Nov 2017 07:08:44 -0400
From: "john at kk9a.com" <john at kk9a.com>
To: towertalk at contesting.com
Cc: andresskurt at gmail.com
Subject: Re: [TowerTalk] Subject: Wind survival + load ratings... vs,

<I own several smaller 40m OptiBeam antennas which have held up fine and
from an RF viewpoint they are fantastic however I have heard the horror
stories about their 80m beams from other tower installers. OptiBeam also
makes a massive full sized 4el 40m which may have the same issues. I asked
Tom once what aluminum he uses and I seem recall a non specific answer
like aircraft aluminum or something like that. It is interesting that high
strength tubing may not be available in EU. Also metric tubing does not
telescope nicely, I wonder how that effects the strength of the joint.
Imperial sized tubing with a .058 wall fits together perfectly making it
easy to homebrew. For my homebrew antennas I only use 6061-t6, I see most
ham suppliers sell 6063-t8. What is the difference?

John KK9A

##  6063-T832 is  39 ksi yield strength.   Done in an air bath.  Comes out shiny.  Cheap to buy
##  6061-T6 is 40 ksi yield strength.   Oil quenched, done in an oil bath.  Cost between double and triple, vs 6063-T832..at least in small sizes.
In bigger sizes, like  2  inch OD and bigger..and with the bigger wall thickness, like .125  or  .120, there is hardly any difference in price. 

##  You can now buy  6061-T8  ( T8 not T6)   for boom material.  Its  .120  wall  vs the  .125 wall  u get with  6061-T6.    .120 wall is superb, since it
telescopes nicely  into the next sized tubing.    DX eng sells it, as does others.  Like  1.5   1.75  2.0   2.25  2.50  2.75   3.00 

##  problem with .125 wall stuff, is u have to turn it down by .05 inches  in a lathe....which is a pita  for us back yard folks. 

#  f12 used a lot of .049 wall stuff on their yagis...which makes for a sloppy fit.  So they do a very light swedge where eles join.   another pita for us back yard folks..if u dont have a swedging tool. 

.375 OD tubing comes in  .027 wall, and also .035,  .049  and  .058 wall 
.5 od and up will typ come in .049,  .058, .065 and also .083 wall.    F12 used a lot of .083 wall in their yagis, like 40m arrays  etc, but that too requires swedging. 

##  I heard that european tubing and esp optibeam al  was as little as 25 ksi when they 1st started out.... then swapped to stronger al.   I cant even fathom using 23 to 25 ksi yield tubing for anything. 
My biggest complaint with eu tubing is its metric...pita.  Non standard wall thickness mean non of it telescopes,  so it all has to be swedged.  Try finding metric tubing in the usa or canada.... near unobtainium.  
A buddy  finally did find a supplier in the usa that carried metric tubing. 

##  real aircraft  tubing is stuff like  2024..which is typ heat treated to aprx 44 ksi.   2024 has a lot of copper in it....and cant be welded afaik.     7075 al tubing is stupid strong, like 70 ksi... but is cost prohibitive for ham applications. 
Local buddy obtained a bunch of scrap 2024 at the local airport.   used it for 15M eles....and they all bent.  Turns out what he got was 2024- T0...which is really soft.   When they build ribs and stuff for small aircraft, they are formed in
jigs, etc.  Then sent off to be heat treated... which is a max of T3   for  2024.   Ok, then its strong.   So much for dumpster diving. 

##  small tubing, like  .375  up to 2 inch od.... in 6061-T6   is now priced into the stratosphere.   F12 and tenedyne both used it.  Everybody else uses  6063-T832, including Mosely, m2, old kln, jk ants etc. 

##  One  2 el  80m  optibeam  just south of me.  ssb + cw switch box was a gong show, design defect..... later fixed.  Then the wrap around square boom to ele clamp assy disintegrated.  The els  were dangling below the boom,
left hanging only by the overhead ele truss lines !   It all got sorted out in the end.... just more crane trips and more $$. 

Jim   VE7RF