[TowerTalk] installing monster masts in towers (and ? two thrustbearings)

[ersmar@comcast.net]

Steve:

     This is a posting I made some time ago on the subject:  http://lists.contesting.com/archives//html/Towertalk/2003-08/msg00163.html .  When I made my posting from a few days ago I had this in mind.  

     However, when I wrote below "...this value [axial load limit] was nowhere near the weight of a typical CM mast, let alone a fully-configured mast/antennas/coax assembly",  what I had in mind was that the setscrews on, say, a two-inch mast could NOT support a typical ham antenna/mast system.   But if you read the specs at the URL in the 2003 posting, you'll see that the slippage value for a two-inch mast made by Ruland (the manufacturer shown) varies from 1200 pounds of axial force (dead weight for a vertical mast/antenna system) to 8000 pounds, depending on the setscrew size.  

     One might be tempted to conclude that in general ALL bearings WILL be able to support the ANY vertical load we hams can build.  The numbers, above, seem large enough.  But the manufacturer states in his Disclaimer at the bottom of his page that these figures represent FAILURE of the setscrew and that the results "are not a guarantee of average values nor a guarantee of maximum or minimum values under all conditions."  

BOTTOM LINE:  The thrust value limit of each bearing is finite and we ought to know what it is and design our tower systems accordingly.

73 de
Gene Smar  AD3F




> In a message dated 6/8/2005 8:53:48 AM Pacific Daylight Time, 
> towertalk-request at contesting.com writes:
> 
> >  Finally (unless you've hit DELETE by now), the set screws do have an axial 
> force limit.  I found on one bearing manufacturer's web pages a value of some 
> finite amount of force along the axis of rotation that the setscrew could 
> withstand.  I cannot recall the actual value, but it is listed.  This would 
> correspond to the dead weight limit of a vertically-mounted Amateur bearing.  As 
> I 
> recall, this value was nowhere near the weight of a typical CM mast, let alone 
> a fully-configured mast/antennas/coax assembly.
> 
>     You had me up until this paragraph. I'm not exactly sure what you are 
> implying. If you could post some setscrew limit numbers, then it'd be clearer to 
> me. I'd be real grateful. Tnx.
> 
> Cheers,
> Steve    K7LXC
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