On 5/15/2010 4:54 PM, K7LXC@aol.com wrote:
>
> In a message dated 5/15/2010 12:01:22 P.M. Pacific Daylight Time,
> towertalk-request@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
>
>
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|