I agree with Steve's statement on binding. I have a middle thrust bearing
and leave it loose during normal operation (i.e., the screws don't touch the
mast.) I'm sure if I tightened the screws the mast would bind and I'd have
to realign the whole drive train from the upper bearing to the rotor plate.
No fun and not necessary.
Although it's possible to do without the thrust bearing, provided you have a
plate and u-bolt, I like having the middle thrust bearing there. While a
u-bolt keeps downward force off the upper thrust bearing screws, it may not
do as good a job keeping the mast from moving horizontally -- i.e., without
the bearing all that's keeping the mast in place is the friction between the
u-bolt and the middle plate. A strong gust could move it to one side. That
may not be a huge problem -- after all, the plate will keep the mast from
moving much. But the mast will have to be yanked back to mate with the rotor
again. Also, without the bearing, the u-bolt rests directly on the plate and
if the saddle isn't thick enough there isn't much room to turn the nuts. The
bearing lifts the u-bolt off the plate and makes it easier to tighten the
nuts.
But if you want to save $100+ the bearing isn't strictly necessary.
73, Dick WC1M
> -----Original Message-----
> From: john@kk9a.com [mailto:john@kk9a.com]
> Sent: Wednesday, August 12, 2009 7:36 PM
> To: TOWERTALK@contesting.com
> Subject: Re: [TowerTalk] One thrust bearing vs. two
>
> I concur, plus the u-bolt keeps the antenna from spinning while the
rotator
> is removed!
>
> John KK9A
>
>
> To: towertalk@contesting.com, tod@k0to.us
> Subject: Re: [TowerTalk] One thrust bearing vs. two
> From: K7LXC@aol.com
> Date: Wed, 12 Aug 2009 11:58:07 EDT
>
> The alleged purpose of the middle thrust bearing is to hold the mast
> vertically to aid in rotator replacement. You don't need a middle
> bearing - all you have to do is capture the mast. You can do that with a
> rotator plate sans bearing or fabricate a mast holder made from a couple
> of pieces of angle iron and U-bolts. You just install it when you need
it.
>
> A mid thrust bearing can potentially add more bind in the rotator/mast
> system. The tolerances are relatively large and some misalignment is
> common.
>
> Cheers,
> Steve K7LXC
> TOWER TECH -
> Professional tower services for hams
> Cell: 206-890-4188
>
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