Date: Sat, 26 Jul 2014 14:27:25 -0400 (EDT)
From: Hans Hammarquist via TowerTalk <towertalk@contesting.com>
To: towertalk@contesting.com
Subject: [TowerTalk] Fwd: Cutting 2" Heavy Wall Cr-Mo Mast Up on
Tower
Beside wonder how you are going to handle the cut-off piece, I would try a
regular tube cutter. I am using one with carbide wheels and that seems to cut
anything. Nothing but hand power is used.
Good luck but be careful.
Hans – N2JFS
## His 22 foot mast weighs 200++ lbs.......which implies it has a half inch
thick wall thickness. A 2 inch od mast..with a .375 inch wall is only 7
lbs per foot. No way in hell you are gonna cut 4130 heat treated
chromolly steel, with a half inch thick wall...with any tubing cutter.
## BTW, once the mast is .25 inch thick, going any thicker is really a
waste of effort. At that point you should use a bigger OD mast, like 2.5
or even 3.0 inch OD. A 2 inch mast with a .375 inch thick wall,
weighs the same as a 2.875 inch mast with a .25inch wall thickness..... both
of em weigh the same 7 lbs per foot. The 2.875 inch od mast will be one
helluva lot stronger, even factoring in the bigger diam masts windload. And
that assumes the 2.875 inch mast is DOM, with 89 ksi yield strength..... vs
the 2 inch mast with its .375 wall being made from 4130 chromolly steel with
107 ksi yield.
## I use a 2.0 inch od mast with a .375 wall thickness...... cuz its stronger
than a 2 inch mast with a .25 wall. However, that was not my choice..since
the HDX-689 I bought used was all setup for a 2 inch mast. If I was doing
this from scratch, I would opt for either a 2.875 inch od x .25 inch wall
DOM mast..... or a 3.0 od mast with a .25 inch wall...made from 4130 chromolly
steel. The strongest mast I ever heard about was 3 inch OD with a .375
wall..made from 4130 chromolly. That mast would weigh 10 lbs per foot..same
as the fellow with his 2 inch od mast and .5 inch thick wall.
## U can see the effect right away using any of the popular mast programs.
watch out, the DOM stuff will vary from 75 ksi to 89 ksi..depending on where
you buy it. 4130 chromolly will vary from 107 ksi up to 125 ksi. The
yield strength makes a huge difference of course. Section modulus x yield
strength = bending moment.
Jim VE7RF
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