Date: Mon, 10 Feb 2020 09:35:44 -0800
From: "Richard (Rick) Karlquist" <richard@karlquist.com>
To: john@kk9a.com, towertalk@contesting.com
Subject: Re: [TowerTalk] Help identifying alloy in mast
> For some reason hams seem to be obsessed with 2" chrome molly masts.
> John KK9A
<Can you expand on your comment about the chromoly obsession?
<I too keep reading the chromoly "hype" (?) here on TT.
<Is it possibly overrated? Or maybe it's the real deal.
<I don't have an opinion as a non-expert; just trying to learn about it.
<Rick N6RK
## Pretty simple matter to calculate all the loads on the
mast....including the mast itself.
Before you overload the mast, do the simple calcs.
## Bending moment = ......section modulus X yield strength, its that
easy.
## A 3.0 inch OD x .25 wall mast weighs the same as a 2.0 inch x
.375 wall mast..... BUT the 3 inch OD mast has a helluva lot bigger
section modulus.
## DOM is typ 75 to 87 ksi....and can not be heat treated.
## Chromolly from the steel yard is UN-HEAT TREATED....and is 70 ksi
yield strength.
Once heat treated, yield strength is typ 107 ksi.... up to a max of
125 ksi.
Heat treatment done at 1100 deg F.
Galvanizing done dead last......and done at 900 F. Galvanizing
process does not affect the heat treatment process.
## Can the XRF gun tell how much heat treatment was done to a CM
mast ??
## That DXE online mast calculator is based on 222-F specs.... which
are bogus imo. 222-F specs are designed to sell CM masts.
Instead use the ... no-spec method..which is the basic wind pressure
you get in a wind tunnel.
## DXEs.... yagi mechanical software provides a choice of 222-C spec,
no spec, 222-d, 222-e, 222-f, 222-G.
JK ants....and myself use the... no spec..... aka basic wind speed
formulae. Its accurate and more stringent than 222-C.
222-F results in a 204-BA up 100 ft.... breaking at 64 mph.....
which is nonsense of course.
## Think of the mast as a giant torque wrench.... except with loads
applied at various points.
## wind speed device really needs to go at top of mast.... not on
the side of a tower. Forget the 6 oclock WX, they wont get it right.
Jim VE7RF
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