40M Beam and Mast

K7LXC@aol.com K7LXC@aol.com
Mon, 3 Feb 1997 22:02:19 -0500 (EST)

In a message dated 97-02-03 17:46:54 EST, johns@in.net (John Scott) writes:

>I got a question for you. Do you think a 4130 Cromolly Mast 20' x 2" x .375"
>would hold a KLM 2 EL. 40 meter beam (45lbs - 6 ft2 - 16' boom) 15 feet
>the tower? I will be using a thrust bearing. Let me know what you think!
Hi, John --

      If you're in Marion County, it's only a 70 MPH wind zone.  With that as
the wind pressure and 6 sq.ft. of windload, the total bending force for the
antenna and mast is less than 25,000 psi.  In this case, a 4130 cold worked
mast rated at 75,000 psi would certainly do it.  It would be $$ overkill. 

     A carbon steel mast with a tensile strength of 46,000 psi with 0.25 inch
wall would do it.  A low carbon piece of cold drawn tubing such as 1016
(50,000 psi) would work.  A piece of CDBW (cold drawn butt welded) 1010 is
rated at 50,000 as well.  Check with your local suppliers for the costs.  

     At 90 MPH, you're looking at over 41,000 psi bending force. If you're
looking at bigger loads on the mast in the future or higher windspeed
capabilities, then the 4130 would be easier to justify.

73,  Steve   K7LXC

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