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

To: Towertalk reflector <towertalk@contesting.com>
Subject: Re: [TowerTalk] Sorry to bring up an oldie - Mast Material
From: Bill <bmarx@bellsouth.net>
Date: Wed, 09 Mar 2011 15:25:43 -0500
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
During Hurricane Katrina we received winds up to 125 mph on the east 
coast of Florida. A tree blew over onto my guy wires taking out my guyed 
and bracketed 50 ft of Rohn 25G and destroying my KT34XA. The four foot 
of Plumbing Schedule 40 pipe extended from the top of the tower was just 
fine.
Bill Marx W2CQ




On 3/9/2011 3:09 PM, Rick Scott wrote:
> What would that look like for 6061-76 its yield is 40,000 I believe.
>
>
>
>
>
> ----- Original Message ----
>> From: Dave Hachadorian<k6ll@arrl.net>
>> To: Rick Scott<w7psk@yahoo.com>; Towertalk reflector
>> <towertalk@contesting.com>
>> Sent: Wed, March 9, 2011 11:31:40 AM
>> 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@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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