Date: Sun, 14 Oct 2012 18:13:25 -0700
From: Grant Saviers <firstname.lastname@example.org>
To: K8RI <K8RI-on-TowerTalk@tm.net>
Subject: Re: [TowerTalk] Choice of aluminum
Some clarifications -
Re the tolerances of tubing diameters: Tube Service provides drawn Al
tube tolerances on their web site, see
For the 1 to 2" od sizes of 6061 or 6063 the numbers are as follows for
max single point diameter deviation +/- 0.010"
maximum point wall thickness deviation +/- 10% of wall thickness or
+/-0.003" whichever is greater
mean wall thickness deviation +/-0.006"
So if one is lucky, 0.125" wall thickness diameter steps might
telescope (at least 0.005" clearance and with plenty of Never-Seez) .
In my experience the mills are controlling to "something sigma", maybe
not Six Sigma, but tight enough to not draw much scrap. So it's a bad
idea to bet against the mill QC department. It would be interesting to
know if TT & DXE ask for tighter tolerances as the above numbers could
cause their wall thickness to interfere if tolerances are at/near the
## .125” wall thick tubing will NOT telescope into the next size up/down !
That’s why with steel tubing they use .120” wall, so it all nicely
## DX eng sells 6061-T8 tubing in .120” thickness’s. Now this solves a
problems in one shot. No more having to machine off .005” in a lathe every
you want to splice 2 x pieces of tubing together. And 6061-T8 is a full 25%
yield strength than 6061-T6 ! The price is the same, so why mess with the
.125” wall stuff,
that doesn’t telescope unless in the lathe.... and is 25% weaker.
## Nothing wrong with using irrigation pipe for 80m verticals, it’s done all
the time. If you
get the 4” OD stuff, it comes in .100” thick..and is plenty strong enough....
The 3” stuff only comes in .050” thickness. I’m sure the fellow in south
america can get
irrigation tubing. It usually comes in 20-30-40’ lengths. One 40’ length
of 4” OD x .100”
thick pipe is 2/3 of your problem solved right there. 2 x solid discs of al..
like a puck shape,
stuffed into the 4” tubing, with the correct holes in the center of the pucks,
would make for a
simple method of reducing diameters to something smaller for the last 22’ of
Most will just splice some more 4” pipe onto the end..to make the remaining
## I recently saw doug, VA5DX’s 80m 4 sq array, and it was all made from 4”
pipe..and guyed. Built like a tank.
Later... Jim VE7RF
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