> In a message dated 10/16/2007 2:48:49 P.M. Greenwich Standard Time,
> finger@goeaston.net writes:
>
> I had a 9-50 up for years with a KT34A on top. Moved it once to a new
> location. Tower was okay but won't last "forever" as the bolt holes at
> the leg junctions elongate over time and sections become useless
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Same experience here. I had two aluminum towers, one from Heights and
> one
> from Universal. Both developed "eggholes". I also found and sold
> several
> aluminum towers with the same problems.
Likewise I've run into the same problem. Actually I've never seen one of the
smaller aluminum towers without egg shaped holes in the legs.
>
> Past opinion on this reflector was "do not drill out the eggholes and
> replace them with larger bolts". The solution to counter the egghole
> development
I'd not drill them out except to cure a *slight* egg shape, but we have to
remember than once this condition is present the legs have been weakened. By
how much? I don't think any one knows, so the tower strength has become an
unknown at this point.
> was to guy these usually self supporting towers. That was also a thumbs
> down
> on this reflector.
I do guy them, but with some caveats. I build a triangular bracket that
fits around the tower with the leg bolts going through the center of the
brackets. I'd recomend a center drilled saddle bracket at the leg bolt or a
U-bolt/saddle bracket just above or below the leg bolt while trying to keep
it on the area where the leg is double thickness. The U-bolt only needs to
be snug, not tight enough to leave a mark in the leg. This also means a
relatively light guy line tensioned appropriatly so as to not over stress
the tower. This ends up moving the guys to a position perpendicular to the
faces of the tower rather than the legs. Also the two Aluminum towers I'm
using are light duty and I treat them as such.
The total pressure on the legs at the base including the amount from guy
tension should not exceed 1/2 (50%) of the rated vertical load for the
tower.
>
> One other caveat...be careful how tight you tighten the bolts on the
> aluminum tower. If you tighten them like you would normally tighten Rohn
> 45/55, it
The bolts need to be properly torqued. Too light and the sections will move
which hastens the "egg making" process.
Too tight and it not only bends them making them difficult to get apart, it
substantially weakens the leg. Again, I've not found a small tower then
hadn't had the leg bolts over tightened, not tightened enough (most were
over tightened), and had rotator plates installed with the U-bolts WAYYYY
over tightened.
Hams in general *seem* to be a bit smarter than this, (there are outstanding
exceptions ofcourse) whether it's due to the towers being better built, so
much more expensive, or the hams in general are a bit smarter, I don't
know. I do know I don't consider the small Alunminum towers suitable for
anything more than supporting a small vertical or wire antennas. The big
"and expensive" ones are a different breed, but they don't last forever
either.
> will be very challenging to get them apart since the aluminum bends
> together.
> This, coupled with oxidation from the joint makes taking them apart
> "fun".
I use a "come along" and a 1 1/2" or 2" nylon cargo strap, a board (3/4"
plywood cut to fit) that is a good fit between the sections, PB-Blaster on
the joints and pull them apart although it sometimes takes a bit of tapping
with either a "dead blow" or rubber hammer on the joints. Generally a 5
minute wait after the PB-Blaster application and they come right apart.
Otherwise a few taps on the joints while they are under tension and the
things literally fly apart.
Normally the mating surfaces are no longer smooth and shiny but look like
some one had thrown a hand full of coarse sand in the joint before putting
it together. The things can be as difficult or even more difficult to put
back together than they were to take apart.
I'm putting a "page" together about my AV- 640 that includes the working
with a couple of small aluminum towers. It shows how I get one apart and put
it back together and No, there aint no way I'm climbing one of those. <:-))
BTW I put them together the same way I take them apart. The come along, a
board, the nylon strap, and tapping on the joints. I haven't found one yet I
could just slip together like my ROHN.
> You can't hammer and beat the sections apart like Rohn 45/55. If you do,
> plan on making a trip to the local welder. Or worse, to your local scrap
> metal
> dealer.
Typically I spend more time using a 5# "dead blow" hammer to straighten
braces than trying to get one apart. Most of the free ones (32 and 40')
appear to have been climbed by the local power lifter who needs to go on a
diet.
With these old towers (Steel or aluminum) I've also found it pays to lay the
tower over some supports to keep it out of the dirt, remove the bolts, tape
the joints and bolt holes, and then apply water under pressure (LOTS of
water) to clean out the legs. The last one yielded over a pint of shelled
corn and about a pint of something that looked like rust. Don't know what
that suff was, but it wasn't used corn that had been through the mice.
The design for many of these towers has the legs "up-side-down" to what we'd
expect and that makes them good water collectors. The top section usually
has the tube open at the top so water running down the mast goes right into
the legs. *Anything* in the legs such as dirt, spider webs, nests, and such
is going to lead to split legs when freezing weather arrives. I've found
split legs not only at the botton but in the curved portion of the top
section.
Although the big Aluminum towers we use are much more resistant to these
problems (better built out of better material) they are not immune. They are
still at the mercy of the guy with a wrench, the nature of Aluminum,
critters, and the elements. OTOH a properly built, installed, and maintained
aluminum tower should last for many years. HOWEVER I must hasten to add that
I helped remove a 20 meter monobander from a friends living room after his
new Heights fold over tower "foldeded over" under a load of ice and put the
monobander through the roof. I'll add this was over 25 years ago.
73
Roger (K8RI)
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