[TowerTalk] [Bulk] Re: Top Bearing Plate for 55G vs Rotor Plate

[Bill Aycock]

Bad lack of understanding or poor wording -- Bending moment is the result of 
applied force and geometry-- NOT material.
Bill--W4BSG

-----Original Message----- 
From: Doug Renwick
Sent: Tuesday, August 12, 2014 12:59 PM
To: 'Grant Saviers' ; towertalk at contesting.com ; rthorne at rthorne.net ; 'Don 
' ; 'Charlie Gallo' ; 'Gary Jones'
Subject: Re: [TowerTalk] [Bulk] Re: Top Bearing Plate for 55G vs Rotor Plate

Here is my take.  A blanket statement  does not fit all situations.  A
middle bearing does have merit.  I cases where a long mast fits inside the
tower or there are stacked antennas on the same mast, a middle bearing will
stop the bending moment in a strong wind.  And a bending moment will be
larger with an aluminum mast.
I put a middle bearing in my towers.  Alignment has not been a problem.  The
middle bearing is loosely fitted so there is some room for motion.  It is
easier to have it there than try and install it later.
Doug


-----Original Message-----

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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