[TowerTalk] Tripod and a bearing

[Steve Maki]

Rick Morris <rick.morris@arris-i.com> wrote:

>I am installing a Cushcraft A50-3S atop a 10' tripod and am using a
>Yaesu G-450A rotor.  The mast will extend about 5 to 8 feet above the
>tripod with the rotor about 5 feet down from the top.  The problem is
>the mast does not have any bearings for the mast to rotate in.  All it
>has is bolts through a collar at the top of the tripod and again in
>another collar about halfway between the rotor and the top of the mast.
>It would seem to me that this would make it difficult for the mast to
>rotate due to the drag on the mast from the bolts. However, a few local
>hams has said this is not a problem.

The local hams are wrong.  The limited strength of this type of tripod
DEPENDS on those set screws being tightened down on something.  Left
loose, the structure has no strength at all.

>The top of the tripod is not like the top of a regular tower section,
>where there is a round-like "tube" for a thrust bearing to rest upon.
>Instead, the top of the tower is essentially three tubular legs with
>flattened ends, and a collar made out of 3 ohm-symbol shaped brackets
>that bolt between the top of each leg.  Each bracket has a bolt through
>it to level the mast.
>
>What I am wondering is if someone knows of a way to attach a bearing to
>the top of such a "tripod", or if one is really needed.
>
>Obviously I am new to learning about towers.

If the tripod's collar is large enough, you could simply cut a short
piece of an appropriately sized larger tubing and clamp it in the top
of the tripod, and the mast would rotate inside of that.

If it is not large enough, than you are probably contemplating the
use of an undersized TV tripod that will cause you grief in the long
run.  Get a good solid tripod designed for this application, or use
a Rohn 25 or 45 top section with a custom base.

--
Steve K8LX

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