Date: Thu, 7 Apr 2016 21:39:52 -0400
From: <john@kk9a.com>
To: <towertalk@contesting.com>
Subject: Re: [TowerTalk] 2 inch Chrome Moly mast needed
My suggestion was to consider a 3" x 1/4 wall 1026 instead of a 2" Chrome
Moly mast. I suspect that 3" 1026 is stronger than 2" 4130 (I don't have a
mast calculator handy) and it is easier to climb. I purchased a 3" 1026 DOM
from steel company and had it galvanized. My costs were significantly less
Array Solutions plus did not want their odd 2 7/8 size. At that time DX
Engineering did not sell masts and no one else sold a 3" mast so making one
was my only option.
John KK9A
##ARRL has a free, dead on accurate mast calculator. You can plug in any OD,
any wall thickness, and any yield strength . Then insert the yagis at any
point above the
top of the tower, windload on each..and it spits out the survival speed in mph.
## fun to play with, esp when you compare stuff like 1.9 OD x sched 80, 35 ksi
pipe vs 2.0 OD x .25 4130 CM.... or 2.0 OD x .375 wall 4130 CM. Yikes,
the
results are more than an eye opener.
## yes, I did on the software, just what you used. I compared 2.875 x .25
87 ksi mast, made from 1026 DOM, as sold by array solutions..... VS 2.0
OD x .25 wall 4130 CM
and the difference is astounding, and then some! Even though the 2.875 mast
is ‘only’ 87 ksi, its
one HELLUVA lot stronger VS 2.0 OD x .25 wall 4130 CM... (107 ksi).
## also tried 3.0 OD x .25 1026 DOM ( 87 ksi) VS 2.0 od x .25 4130 CM
(107 ksi) and of course
the difference is even more. Its also a helluva lot stronger than the 2.0 x
.375 4130 CM mast I use myself.
## Im stuck with a 2.0 O mast, with the HDX-689 tower, since the top of tower
+ mating tube /plate assy directlybelow the
tower + both thrust bearings are all set up for 2.0 OD. The sleeve tube
between top plate and 2nd plate, that is a few inches
below the top is all welded. I bought the tower used.... and would highly
NOT recommend choosing a 2.0 OD mast to
anyone. Whoever standardized the 2.0 OD mast was fubar. Plan B was I
bought a 20 ft long x 2.0 OD x .375 wall
4130 CM mast... 107 ksi. It weighs a whopping 140 lbs, with 14 ft of it
above the tower. two trust bearings used, peer brand,
plus the UST sleeve tube assy, plus the K7NV small PP that hangs below the
rotor plate. It’s the best I can do. My 1st
choice would be 3.0 x .25 4130 CM..since it weighs the same as my 2.0 X .375
mast..and cost the same.... yet the 3.0
mast is a magnitude stronger.
## the strongest mast I heard used was by Blackie, W6HLH, back in the mid
70s. 3.0 OD X .375 wall, 4130 CM,
115 ksi. The highest I have seen 4130 CM heat treated to is 125 ksi.
115 ksi was quite common, and also 120 ksi.
In recent years, the heat treated CM has gone down in ksi. Most are 105-107
ksi range.
## Local engineer would only accept a 2.0 x .375 wall CM mast..barely.
What else I have seen used is
2.5 OD x .375 4130 CM.
Jim VE7RF
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|