[TowerTalk] Re: Thrust bearing

[Jerry Keller]

The point about mast expansion is very interesting, but am I correct in thinking that it wouldn't produce any problem if the weight of the mast and antennas is borne by the clamps bearing on the thrust bearings, and the mast is not gripped by the setscrews in the thrust bearings? It seems to me the worst that would happen is the rotor might get more load temporarily, as the mast expansion lifts the load off the TB's, then contracts to put it back on.

73, Jerry K3BZ
  ----- Original Message ----- 
  From: Tower (K8RI) 
  To: towertalk at contesting.com 
  Sent: Thursday, July 22, 2004 5:38 PM
  Subject: Re: [TowerTalk] Re: Thrust bearing



  Likewise, I use two thrust bearings and unlike others here, I use the thrust
  bearings to support all the weight of the antenna system which is
  substantial. Probably on the order of 600#, give or take. They maybe crude,
  but I think they are far more rugged at supporting weight than most rotors
  such as the tail twister and HDR 200s and 300s.
  In all the years I've used the ROHN thrust bearings I've never had one
  fail.OTOH, prior to the PST61 rotors suffered very short life spans.
  Nothing would hold that system including the big Hygain HDR 300s.  I use the
  plural as I went through two of them in almost as many weeks.

  One thing about using two thrust bearins, or even one for that matter.  The
  mast is clamped in the bearing(s) and rotor.  The mast changes length with
  temperature.  To reduce bending moment the mast should extend below the top
  of the tower about as far as it extends above the top.  If the mast is
  Aluminum it will expand and contract much more than the steel tower and can
  put tremendous strain on the top of the rotor, in either, or both pushing
  and pulling.  With Aluminum masts in Aluminum towers and steel masts in
  steel towers the differential should be minimal.

  Roger Halstead (K8RI, EN73 & ARRL Life Member)
  N833R, World's Oldest Debonair (S# CD-2)
  www.rogerhalstead.com


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