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

 To: "Rick Scott" , "Towertalk reflector" Re: [TowerTalk] Sorry to bring up an oldie - Mast Material "Dave Hachadorian" Dave Hachadorian Wed, 9 Mar 2011 12:31:40 -0700 mailto:towertalk@contesting.com>
 ```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 _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
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