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## [TowerTalk] Mast and Thrust Bearing questions

 To: "'Tower Talk Reflector'" [TowerTalk] Mast and Thrust Bearing questions "Christopher J Galbraith" Fri, 7 Jul 2006 11:09:36 -0700
 ```Hi gang, We are getting closer on our roof-top 40 ft tower design, but could really use some input on the following related issues: 1. How much mast to put inside the tower? We are going to use either 4130 or 1026 DOM, 0.25" wall, 2" O.D. and need 10-12 ft of mast extending from the top of the tower. We've done the calculations for the bending moment, but this only applies to the mast at the point where it meets the tower. How does one decide how much mast to place inside the tower? Is there a rule-of-thumb for how much mast to place inside the tower, to reduce the side-to-side forces on the rotator? 2. Should we use multiple thrust bearings, and if so, where, and what type? Some installations we've seen use a thrust bearing at the top of the tower, then another thrust bearing at some point in between the top of the tower and the rotator (within the tower). Is this a good idea, or overkill? I've seen many reports of failed Rohn thrust bearings. So, we are planning to use Array Solutions' heavy duty thrust bearings. Are there other options someone can recommend? Finally, for background, here are some details on this tower/antenna system: 1. 40 ft of Rohn 55, guyed using a torsional guy system, on top of 5-story building 2. Antennas on mast include large 10-20m Yagi (15 ft^2) at 1 ft above tower, and 6m Yagi (3 ft^2) at top of mast (10-11 ft above tower) Thanks very much for any input! 73, Chris KA8WFC _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread [TowerTalk] Mast and Thrust Bearing questions, Christopher J Galbraith <= Re: [TowerTalk] Mast and Thrust Bearing questions, bob finger Re: [TowerTalk] Mast and Thrust Bearing questions, K8RI on Tower talk Re: [TowerTalk] Mast and Thrust Bearing questions, David Robbins K1TTT Re: [TowerTalk] Mast and Thrust Bearing questions, K8RI on Tower talk