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[TowerTalk] Cleaning tired aluminum tubing

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Subject: [TowerTalk] Cleaning tired aluminum tubing
From: (Roger L. Elowitz)
Date: Sat, 21 Jun 1997 00:07:26 -0400
Hi Grant, and all you shiny tower and beam builders,

I can speak with great authority about this business of restoring antennas
to their pristine bright and shiny beginnings.  Last summer I did just that
with a fifteen year old Mosley TA-33.

I used everything from steel wool to ScotchBrite pads on an electric sander.
I got absolutely filthy.  I breathed far too much aluminum dust and... I had
a wonderful time for someone who has nothing better to do in retirement.
(Ha!  Had to stick that comment in for all you working stiffs!)

But for the rest of you normal folks out there contemplating the same
"stupidness," let me assure you that all your wonderful efforts to make that
tubing shine.... are totally for naught if you are thinking it will, in any
magical way, do a damn thing for your signal.... and I don't care how mangy
that tubing looks.

That dull gray coating on that well weathered tubing is great stuff.  It's
called aluminum oxide, and, unlike it's iron counterpart (iron oxide or
rust) is a non-flaking, non-destructive, albeit very, very ugly coating. I
don't believe anyone in his right mind ever compared tubing with and without
it for radiation efficiency.  Guys with ten or fifteen year old beams only
notice the change in sunspot activity and don't blame their antenna's
appearance for the disappearance of the dx... I hope...;-)

All that said and done...... as long as you have the monster on the ground
and in pieces... why not just clean up the tubing sections where they
overlap.  Clean the inside of the tubing too (only where it contacts the
piece that's inserted.... of course) with some SkotchBrite pads on a dowel.
Then, you can apply the conductive grease to the joints before you
reassemble them.  

The grease will more than likely do little or nothing for the RF
conductivity of the joints but rather, it will keep the mating surfaces from
oxidizing and bonding to each other... preventing you from ever removing
them again if they are uncoated!  And aluminum oxide... unfortunately, is a
lousy electrical conductor.  The conductive grease I believe, mostly
provides a barrier against air and moisture from contacting the aluminum
which then oxidizes.  You'll realize this immediately when you get that
grease on your hands or clothes and find it such "fun" to try and remove.
It should come with a warning lable that says... "Warning! Contents have
been known to cause user to curse uncontrolably!"

(At this point in the discussion I scratch my head and wonder... since RF
flows on the surface of the conductor...[skin effect]  how does the aluminum
oxide coating affect the rf... or for that matter... any surface coating
like lacquer?....  Probably makes not an iota of difference at HF frequencies).

The real RF connections are made with the sheet metal screws or rivets or
bolts with star washers and nuts mating the tubing sections.  And this is a
great time to chuck all that old galvanized hardware and spring for all new
stainless stuff.  The next time the antenna is down for overhaul... it'll
come apart without breaking corroded nuts and bolts and fingernails all over
the place.

Oh! I almost forgot.  I've often been advised to place a length of
clothesline rope inside your beam elements to prevent or absorb destructive
harmonic vibration.  This is indeed a neat idea and it doesn't add much
weight.  Another thought is to slide in some loose-fitting wooden dowels for
the same purpose... which does add some weight.  

Then, if it's a trapped beam.... and you can remove the trap covers...
inspect the coils inside for good mechanical (electrical) connections.  I've
found things like loose sheet metal screws holding coil ends... resulting in
intermittent connections.  I've also found cracked coil forms.  By all
means... it's easier to check and fix while on the ground.... before it goes
up.  And do carefully note which end of the trap goes where.  And, lest we
forget... if there are "weep holes" in the trap covers... Yes!  They must
face DOWN or your traps will start doing funny things as they fill with
water and freeze..... Oh!  I can see it now!  Yipes!

Put the thing together paying particular attention to coating stainless bolt
threads with Permatex or the like... to prevent galling as you get nuts real
tight, and, after you've done a thorough job of waterproofing your coax
connections (as advised in previous posts)  you're all set to "go for it."

Now, from a personal perspective only.... I can't imagine doing all that
work and NOT have this beastie shine till it hurts.  So... go right ahead...
double or triple your work effort.  Shine 'er up and coat her with several
coats of Krylon Crystal Clear... to keep her shining... and you'll be
happy.... because that's all that matters anyway!  Go for it Grant!  And
don't forget the Anti-Static Cling Free to eliminate the rain static...;-)

The ol' beam polisher.... (and mole killer),
Roger, K2JAS
(c) 1997 "The Art and Love of Beam Restoration"

At 05:11 PM 6/20/97 +0000, you wrote:
>I recall that in the past months, the subject of cleaning corrosion from
>aluminum tubing has come up. At the time, I had no need, but... I picked up
>an old Butternut vertical that I would like to restore and use as a backup
>antenna. So..., I would appreciate some input on best how to clean up the 
>aluminum crud and warts. My off-hand method would to carefully use a fine
>emery paper .
>corroded in the east bay
>Grant  K7GT
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