The size of the 118,000 psi yield strength chromolly mast I posted is: 2
inch O.D. x 3/16 inch tk wall. I use an 18 foot length for my mast. It
weighs about 80 - 90 pounds (I don't know exactly, but I was able to
lift it myself and walk around with it.) It sits in the tower and is
supported by two thrust bearings 30 inches apart. It's free-wheeling,
turned by a RingRotor at the top of my tower.
It's all described with photographs on my website, as many of you know,
at: http://www.erols.com/n3rr
Bill, N3RR
donald.s.tucker@exgate.tek.com wrote:
>
> I placed 2 questions as a new subscriber out on the reflector yesterday.
> One generated a lot of comment and the second a lot of sources. Some were
> copied to the net, others weren't so thought I would share the information I
> received.
> __________________________________________________________________________
>
> The first question, where can I get a two-way locking winch for raising and
> lowering (tilting over) my motorized crank up. Sources suggested:
>
> Fulton and others (carried by W. W. Grainger or Northern Electric)
>
> US Tower
>
> Northern Hydraulics/Tools/Equipment 1-800-533-5545
>
> Farmtek (www.farmtek.com)
>
> I will check each of these out and thanks to all for generously sharing this
> information.
> ----------------------------------------------------------------------------
> ---------------------------------------------
>
> The second question had to do with my 24 foot piece of 1/4" wall 2" OD
> 6061-T6 tubing which I planned to use as mast material.
>
> Many suggested throwing it away (can't do that of course, it isn't cheap
> even at the mill price). Most favored the use of a chromolly mast. Well
> all I got is what I got at this time. I had not intended to have but just
> enough mast sticking out of the thrust bearing to hold the KLM 40M monopole
> (not a 2-element folks), the TH7DXX and hopefully, a small 12/17 beam (OK,
> and a small 12 el 2M yagi). My intent was put the rotator plate down about
> 4 more feet within the tower and put a simple thrust bearing on a plate
> where the rotator would originally have gone.
>
> Yield strength for the 6061-T6 was stated by one commenter as 35,000 psi as
> opposed to 118,000 (no one indicated the wall size of this 118,000 psi ys
> tubing?) for the chromolloy and that the windload I was proposing was a
> situation demanding a mast with 50-60,000 psi yield strength. I will assume
> this is correct. A statement was also made that the windspeed spec for
> Washington County OR was 80 MPH. Now I've lived here even through the '64
> Columbus Day storm and have never seen winds even near this, but I'll accept
> this as an engineering design spec the county has (who set the spec?).
>
> Everyone generally agrees that the 6061-T6 1/4 mast will have less yield
> strength than a chromolly mast of the same diameter but that the 6061-T6 1/4
> wall 2" OD mast will suffice if my wind load is within the yield strength of
> the mast. It appears that I may have to put the wind-load numbers together
> and go to my old text books to see if I'm ok and what I may not be mounting
> for now.
>
> I want to thank all of your for your input and advice.
>
> Don W7WLL
>
> --
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