[TowerTalk] Sorry to bring up an oldie - Mast Material

[Jim W7RY]

Try Metal Supermarkets.  Hopefully you have one in your area. They will sell 
you anything in any length. Even cut it for you.

http://www.metalsupermarkets.com/

I buy all my amplifier building stock cut to size from them. Good folks.

73
Jim W7RY


--------------------------------------------------
From: "Dave Hachadorian" <k6ll at arrl.net>
Sent: Wednesday, March 09, 2011 11:31 AM
To: "Rick Scott" <w7psk at yahoo.com>; "Towertalk reflector" 
<towertalk at contesting.com>
Subject: Re: [TowerTalk] Sorry to bring up an oldie - Mast Material

> Here is a neat mast calculator:
> http://www.math.niu.edu/KARC/mast/
>
> Plugging in some numbers for 1.5" schedule 20 water pipe:
> Safety factor f   2
> Wind loading factor k  .004           lb/ft2/mph2
> Maximum stress S       30,000      psi
> Outside diameter D        1.9     in
> Inside diameter d        1.61     in
> Total length of mast          8   ft
> Height above support h       4      ft
> Antenna 1 height h1          4   ft     area a1  6.1       ft2
> Antenna 2 height h2             ft     area a2         ft2
> Antenna 3 height h3             ft     area a1         ft2
>
> Survival velocity:     63.0 mph
> Failure velocity:     89.1 mph
> Weight of mast:     21.79 lbs
> ---------------------------------------
> As indicated above, I wouldn't be confident in using Sch 20 water
> pipe.  That 30,000 psi yield strength for water pipe is hard to
> prove, because water pipe is not specified for structural
> purposes. Also, the last time I priced water pipe, I was amazed
> to see how expensive it had become.
>
> You are much better off using structural tubing, which has a
> specified yield strength.  If you go to a metal supplier and ask
> for structural tubing, he should be able to quote you some prices
> on various strength material. You will probably have to buy a
> 20-footer though.  Another thing you can do is to order some
> galvanized steel mast from Texas Towers. They will sell you a 10'
> piece for $139, and cut off a foot, which makes it UPS-shippable
> (at least the last time I did it, in 1978). Their material is
> 87,000 psi.  Plugging that into the calculator:
> ---------------------------------------
>
> Safety factor f                2
> Wind loading factor k      .004       lb/ft2/mph2
> Maximum stress S      87,000       psi
> Outside diameter D       2      in
> Inside diameter d        1.75     in
> Total length of mast          8   ft
> Height above support h       4      ft
> Antenna 1 height h1       4      ft     area a1   6.1      ft2
>
> Survival velocity:     107.0 mph
> Failure velocity:     151.3 mph
> Weight of mast:     20.07 lbs
>
> That will definitely work.
>
>
>
> Dave Hachadorian, K6LL
> Yuma, AZ
>
>
>
>
>
>
> -----Original Message----- 
> From: Rick Scott
> Sent: Wednesday, March 09, 2011 10:51 AM
> To: towertalk at contesting.com
> Subject: [TowerTalk] Sorry to bring up an oldie - Mast Material
>
> Im really confused.  Id like to buy Local, because the mail order
> houses have
> Really high prices and high shipping
> plus they only do 5 or 10ft intervals.
>
> Ive seen all manor material from them from chrome molly to
> Aluminum and AES even
> has Fiberglass.
>
> I have a Glen Martin 9ft roof mount tower.  Its just shy of 4ft
> from the rotor
> to the top of the tower.  Right now I have
> a 2 1/2" Fence Post mast (really heavy wall) that I hold an A4S
> up with.
>
> A4 is going bad so I decided to get my dream antenna the standard
> SteppIR 3
> element beam and nothing else will go on the mast.  I would
> like to get 8ft as that will give me 4ft above the tower, I can
> put the antenna
> at 2 - 3 feet and be ok.
>
>
>
> So I need 2" mast material,
>
> I would dearly like to buy local and we have a few metal shops
> but I need to
> know exactly what I have.
>
> I searched the forum and man there is a lot of material.  K7XLC
> used to sell
> mast but his site doesnt.
>
> I posted on the local Snohmish County hams and I got a gazzilion
> answers.
>
> One guy swears by Home Depot stuff
> One says only buy Sched 40pipe nothing else needed
> Another says this and that.
> Another says 6061-T6 Extruded Tubing
>
>
> So not really wanting to open a can of worms, whats the best
> material to hold
> what I plan to put up
> for the best cost.
>
>
> Scotty W7PSK
>
>
>
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