[TowerTalk] Best mast location? now muliple thrust bearings

[Roger (K8RI)]

On 5/15/2010 4:54 PM, K7LXC at aol.com wrote:
>
> In a message dated 5/15/2010 12:01:22 P.M. Pacific Daylight Time,
> towertalk-request at contesting.com writes:
>
>    
>>   For various reasons (some inherent in bearing  manufacturing tolerances)
>>      
> three spaced bearings are almost never done in  machinery - it's just too
> hard to get them/keep them aligned.
>
> And this is in more precision machinery  than you'll ever find in tower
> components. The purpose of the middle "bearing"  is to capture the mast so that
> you can do a rotator swap on a top-heavy mast  and antenna array. A simple
> plate with a hole in the middle (e.g. AS25G, 45G,  Trylon, etc.) is PLENTY.
> It's not going to go anywhere. Lacking a middle  plate, you can still
> capture the mast with some angle iron and U-bolts. It's  not difficult to
> fabricate and use.
>
>      And I still think that top mounted thrust  bearings are a ham radio old
> wive's tale and not necessary. All you want  to do is hold the mast against
> horizontal wind forces - the vertical forces  can go to the rotator in most
> cases with no problem.
>    
I'm in the process of replacing all of them here with DOM sleeves (with 
Grease zerks) that just fit over the mast. I will be installing a second 
sleeve of the same size floating, or held in place with set screws just 
above the sleeve/thrust bearing.
The mast does not go all the way to the bottom of the mast clamp in the 
rotator so a rotator swap only requires tightening the set screws in the 
sleeve above the thrust bearing and the rotator can be slid right out.

The sleeve is far more rugged than most thrust bearings.

If using painted masts (good idea) the thickness of the paint must be 
taken into consideration when purchasing the material OD of inside piece 
and ID of outside piece. Remember just 1/16" of paint it a total of 1/8" 
difference in size.

73

Roger (K8RI)
>
> Cheers,
> Steve     K7LXC
> TOWER TECH -
> Professional tower services for hams
> and author of UP THE TOWER - The Complete Guide To Tower  Construction
> available from _www.championradio.com_ (http://www.championradio.com)
> Cell: 206-890--4188
>
>
>
>
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