Don,
Actually, the UHMW bearing design I am using will take axial as well as
radial loads. A 6061 collar is SS 1/2-13 set screwed on the mast &
backs a 5" diameter 1/4" thick 6061 plate fastened to it with FHMS. The
UHMW takes the radial loads and the top of the UHMW is the axial (true)
thrust bearing against the 6061 plate. Not my invention, Brad K7ZSD
used this for his 4 side mount 3"x 20' masts as well as the top
internally mounted rotator/mast. He used white 3" UHMW which showed
some crazing and virtually no wear after 7 years, so my upgrade is to
black 4" UHMW. I'm using 6" square blocks which makes the boring and
mounting bolt design easy. UHMW plate is far cheaper than rod.
Grant KZ1W
On 8/12/2014 10:15 AM, Don wrote:
THAT is a good idea, the UHMW bored block. Zerk fittings and the plain
old typical steel inlanders use go quickly here. Living on the OR
coast next to the ocean you learn quickly that putting antennas
together and mounting them requires 'different' approaches to keeping
them in a low maintenance mode.
I also use the Lear compound, CorrosionBlock, on anything that turns,
slides, screws or moves. Won't wash out and has no metals, RF neutral.
Put onto this by the fleet folks up in Newport who apply it to all
their electrical connections, AC, DC and RF. I've easily taken
elements apart where the salt spray has literally 'grown' on the
element exterior. It is lightly colored so it is easy to see where you
are putting it. See
http://www.learchem.com/userfiles/Industrial%20Strength%20Protection.pdf
for some information.
Don W7WLL
-----Original Message----- From: Grant Saviers
Sent: Tuesday, August 12, 2014 9:52 AM
To: towertalk@contesting.com ; rthorne@rthorne.net
Subject: Re: [TowerTalk] [Bulk] Re: Top Bearing Plate for 55G vs Rotor
Plate
I agree with Steve that a middle bearing is not a good idea as aligning
3 bearings is very difficult and a middle bearing serves no purpose at
rotator rpms.
However, a middle support plate with a removable u-bolt or clamp, that
can constrain the mast when you want to raise it to remove the rotator
for service is a big help. Then the mast stays in column and doesn't
overload/twist the top bearing.
I also dislike the commercial "thrust" bearings. A block of black UHMW
3" thick bored for the mast od will never need servicing. Or stack up
some HDPE kitchen cutting boards bored to fit, but they will need a coat
of paint to protect them from UV. A rotator sized for a 4L full size
40m beam bearings can easily handle a 500lb thrust load. btw, my 40m 3L
full size OWA weighs 350# plus 150# for the 3" x 0.25" wall alloy mast
(a must for that size antenna).
Grant KZ1W
On 8/12/2014 8:04 AM, K7LXC--- via TowerTalk wrote:
I'm working on getting the parts together for a Rohn 55g tower.
? The Rohn 55g Bearing plate sure is expensive. I see two other
possibilities.
1 - Use the less expensive beacon plate and drill a hole for the
mast/bearing.
2 - Use a rotor plate for the same purpose.
I plan on having a top bearing, an intermediate bearing then the
rotor.
I have no idea what the thickness of the Rohn bearing plate is as
compared to a beacon or rotor plate. I'm hoping to put up a full
size 4
element 40m beam some day, so the system will need to handle a good
300+lbs.
Hiya, Rich --
The beacon plate is FB if you don't mind drilling it.
As for an intermediate bearing, I'd discourage it. The plates are not
precision items and you'll just introduce bind into the system.
Since all
you're trying to do is capture the mast, put the rotator plate in
the middle
and skip the bearing - cheaper too. And the upper TB carries all the
weight anyway so a middle bearing doesn't provide any structural help.
Cheers & GL,
Steve K7LXC
TOWER TECH
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