Here is my take. For the amount of money that you are going to put into
your Rohn 55 install, the amount of money to do the top section right (that
is by engineering spec) is a drop in the bucket to get a system that holds
together over time. I'd invest the money to do it right. It will cost less
over the long run, in my experience.
73
Gary W5FI
On Tue, Aug 12, 2014 at 11:52 AM, Grant Saviers <grants2@pacbell.net> wrote:
> 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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>>
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