Gentlemen,
I have read the thread with interest, and here is my solution. Back in
1978, and in order to cope with the likely forces applied to a tower top
thrust race, I looked at the commercial products available but chose to
"engineer" my own, making use of roller bearings to provide a more
effective solution.
I looked for taper roller bearings with a centre bore of 2 inches or more,
and by using a commercially available two part metal collar, clamped
around the antenna support shaft, with the lower edge of the collar
resting on the edge of the inner ring of the taper roller bearing, as the
antenna shaft passed down through the bearing, the weight of the antenna
is transferred to the inner ring of the bearing. The taper aspect of the
roller bearing performance will cope with any radial forces applied to the
bearing.
New, taper roller bearings are quite expensive, but a metal scrap/vehicle
breakers yard will provide a very cheap source, especially if you are
prepared and able to remove them yourself. The taper roller bearings I
used, came from the rear wheel hubs of scrapped heavy goods vehicles, and
they are more than capable of handling the largest antenna related stress,
and better still, cheap, they cost about $1 each!
Of course, the bearing unit requires a "housing" in order to be fitted to
the tower top plate, but again, the same scrap source provided short
lengths of suitably sized, thick walled aluminium tube, in the form of
scrap "offcuts" sold by weight. I was able to fabricate a very acceptable
"product", and fitted with a suitable weather protection "hat", i.e a
scrap aluminium container lid, and the bearing well packed with grease,
one such unit has been in position since 1979.
Sincerely, John. G3JVC/GM3JVC.
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