Hi Jose,
Looks like 1020 DOM has a yield strength of around
60,000 ksi. That is going to be somewhere between 1/3 and
1/2 the strength of a good chrome moly alloy mast with the
same cross section. Leeson's book for example lists the
yield strength of 4340 alloy steel w/ a 1550 degF quench
and a 1000 degF temper as 162,000 ksi. I have seen certs
on other moly alloy masts that were anywhere between
105,000 and 120,000 ksi.
In any case, not sure whether you need this for your home
QTH in Virginia beach or KG4SB, but in either case you'll
be in Hurricane country, so you should probably design for at
least 50psf (lbs/sqft) wind pressure (~110 MPH). The Force
12 website lists the wind area of the 4BA as 7.2 sqft, so
your are looking at something like 50 x 7.2 = 360 lbs of side
load from the 4BA. Across a 10ft lever arm that would be
3600 ft*lbs of overturning moment from the 4BA.
With a 2" x 1/4 wall thick 1020 DOM mast (60,000 ksi),
your maximum load will be about 2700 ft*lbs, which means
your mast could be overloaded in very high winds. You
might want to consider going to a chrome moly alloy instead
of the 1020 DOM. By spending a few extra bucks on moly,
you can effectively double or even triple the strength of your
mast without increasing its weight significantly. You could
increase the wall thickness of the 1020 DOM, but that
doesn't buy you much. You add a lot of weight and even if
you went to 2" O.D. solid rod, the strength of the 1020 DOM
mast would still be significantly less than that of the 2" OD
x 1/4 wall thick chrome moly alloy mast.
Good luck. Sounds like a nice antenna system you are
putting together.
73 de Mike, W4EF.......................................
----- Original Message -----
From: "N4BAA - JOSE CASTILLO" <n4baa@cox.net>
To: <towertalk@contesting.com>
Sent: Thursday, February 10, 2005 12:23 PM
Subject: [TowerTalk] 1020 DOM MAST
> Would appreciate any comments on 2" OD 1020 DOM mast material.
>
> I am planning on putting a FORCE 12 4BA 10 feet over a 5 ele
> 20 METER monobander on a 40 foot boom.
>
> I will need 18 feet of 2" OD mast. 8 feet is in the tower
> with two thrust bearings...and 10 feet outside the tower.
>
> Your comments are very much solicited.
>
> 73's
>
> Jose Castillo
> N4BAA and KG4SB
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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