Call Search

New to Ham Radio?
My Profile

Friends Remembered
Survey Question

DX Cluster Spots

Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement

donate to eham
   Home   Help Search  
Pages: [1]   Go Down
Author Topic: Tower rotor,or thrust bearing holds the weight  (Read 10601 times)

Posts: 4

« on: May 24, 2011, 02:52:43 PM »

I have a newer tower setup and is still on the ground.
Does the rotor hold all the weight of the antenna and mast, or the thrust bearing stop the weight on the rotor? I have asked others and hear both sides. If the thrust bearing does not, why then the support screws and nuts to hold them in place. I have thought of the slop is why the thrust bearing has the screws. On the other hand why does the rotor company show the max weight for there rotors?


Posts: 21764

« Reply #1 on: May 24, 2011, 03:07:36 PM »

Rotators have different load ratings for weight and aren't always used with thrust bearings.

I've tried this both ways with the popular Hy-Gain HAM-IV type rotators (and also the T2X), placing all the weight on the rotator, or lifting it off and letting the TB carry it, and can't see any difference in operation or rotator longetivity either way.

I like having a TB in place so I can remove the rotator altogether and slip the mast down into the tower so service antennas on the mast, or replace them, etc.  The TB can support the load by itself, without any rotator in place, and that's handy; although in addition to the TB I usually tighten up the mast clamps on the lowest beam anyway each time I do this, just in case. Wink

Posts: 1209


« Reply #2 on: May 24, 2011, 04:45:45 PM »

When properly mounted, the TB will absorb some of the downward load but the rotor holds most of the dead weight. The TB is there to take the side loading during strong winds to prevent the rotor from having too much of that as rotors aren't designed to take a big side load like that from a long rotor mast and high winds could produce. All the TB I have seen have adjustment screws for centering the mast in the middle of the TB opening. Personally, I'm not sure I would allow the TB to hold the entire load of a long mast and antennas without some sort of dead weight bracing at the bottom of the mast but then I haven't tried it so I will bow to those who have done it and had success.

Gene W5DQ
Ridgecrest, CA - DM15dp

Posts: 2280

« Reply #3 on: May 24, 2011, 06:06:30 PM »

I'd offer that while the rotator can support the weight of the antenna(s) and mast, having the ability to take the vertical load off the rotator's bearing race will certainly add to its longevity. ...and as Steve says it also makes it very easy to remove the rotator for service should the need arise.

If you disassemble for instance a Rohn TB2 or TB3 for refurbishing, you'll see the ball's primary contact is between the races in the top and bottom faces of the bearing and not between the inner and outer  walls.  To me, that implies that a TB3's intended primary function is to carry axial loads. It comes as a bonus that a TB3 also transfers radial (wind) loads to a degree.  The three large bolts in the rotating part of the bearing woud also indicate that they're there not only to center the mast, but to transfer the vertical load to the bearing. I would think if your primary concern was transferring wind loads rather than carrying weight, then a radial bearing is what should be used rather than a thrust bearing.  In that case the bearing would function as just a well-lubricated bushing.  I don't think I've ever seen one of them on a tower!

Finally, this from Timken's site:
"Thrust bearings are designed to manage thrust (axial) loads and provide high-shock-load resistance in a variety of applications......."

Posts: 126


« Reply #4 on: May 24, 2011, 06:25:58 PM »

I have used a radial type 2" bearing for a long time. Such can still withstand plenty of thrust load (~300lbs in this case), but in my location wind load is more of a concern, and I want to be able to rotate in the daily near gale force wind gusts. I have a peculiar rotor which can not take any thrust load. That plain vanilla 2" Timken is taking the whole load without problem. I just keep it greased and covered with rain protection.
Pages: [1]   Go Up
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!