Dick Green WC1M wrote:
> 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.
>
Alignment of multiple bearings is not all that difficult as long as the
shaft is straight and the positioning of the bearing(s) are adjustable.
The accessory shelves for my 45 G let me easily position the
bearings, or rotator depending on the bolt configuration. Also I had to
open up the bolt holes for the rotator. The most difficult is the top
one which you do first, then the rotator, and finally the mid bearings.
Sleeves are actually more difficult as they have to be mounted
perpendicular to the mast so getting the rotator plate flat is essential
and of course you only have a few thousands leeway getting the sleeve
perpendicular to it's base.
Using the proper size DOM I create the sleeve about 6" to 10" long and a
collar about 4" long and the same size as the sleeve. The sleeve really
only needs to be about 4" long. The shorter sleeve makes the assembly
alignment a bit less critical. The collar is mounted above the sleeve
and with large set screws can support the mast on top of the sleeve when
removing the rotator. Normally there'd be about 1/16th inch clearance.
Put zerks on the bearing, grease the snot out of it, and fasten a wrap
of silicone rubber...or just old inner tube around the collar and over
the joint to keep water out of the sleeve. I prefer white Lithium
grease as it handles the sub zero temps well, or at least the ones we
see in Michigan. It also has a high enough viscosity that it won't melt
and run out on the hottest summer days.
This approach keeps the mast centered, makes removing the rotator easy
as well as working on the antennas.
Just remember to assemble it in a manner that will keep water out. Get
water in a sleeve in freezing weather and you'll need a "heat tape"
wrapped around it to warm it up before you can turn the antennas.
73
Roger (K8RI)
> 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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