Hi Tim,
I've inserted a few comments below:
Tim Totten, N4GN wrote:
> I'll admit up front that I don't have time to read the incredible volume
> of postings to this reflector; I try to skim the subject lines and only
> open maybe 5% of the messages. So maybe I missed something in this last
> thread on gin poles.
>
> The most important thing I learned is that the Rohn gin pole is not rated
> for lifting 55G sections. That got my attention! What is the weak point?
> Is it the mounting or the actual pole? Forgive me, but I've never
> actually seen a Rohn gin pole.
I am not sure of the actual rating on the Rohn EF2545 Gin Pole. By the way,
Rohn calls
them "Erection Fixtures" if you ever want to look one up on the Rohn web page
and you
can't any reference to gin poles. I have heard (I can't remember ever
personally trying
it) that a Rohn EF2545 won't clamp around a 55G leg. 55G legs are just a
little larger
than 25 or 45 legs and I suspect you can't use the EF2545 on 55G. This may be
Rohn's
subtle way of trying to make sure you don't overload it . . .
> For the 45G, I used a gin pole that I bought from an individual who makes
> them. In fact, it was someone recommended on this list, but I can't
> remember his name/call. Not WB0W. It clamps around a leg with a very
> sturdy looking "door" that is hinged to a piece of angle. I can't imagine
> it failing under the load of a single 55G section. But then I guess I
> don't have any guarantees, and I can't even remember who made it. Any
> thoughts?
You might have gotten your gin pole attachment from K7PN who make a very strong
one,
which incidentally, works on 25, 45, and 55 just fine. As far as rating is
concerned,
it would take a rather large engineering effort to calculate all of the various
stresses
on a gin pole to be sure of what its actual rating might be. K7PN's approach
is to just
make it as strong as he can (it is VERY strong) and use it carefully until he
has
confidence about what loads it can safely handle. He has used it to set MANY
55G towers
without any kind of failure. Paul (K7PN) has made a number of these same gin
pole tower
attachments for other people and I have never heard a complaint. He just made
one for
me to replace the one I so generously "gave" to some unknown "friend". In
fact, he made
me two so I can have one to sell. I will be taking pictures of it and putting
them on
my web page in the next couple of weeks. Standby, I will notify towertalk when
the
pictures are up and the pricing is done.
> If the Rohn gin pole is not supposed to be used for 55G, what
> DO people use, other than a crane?
I hope you get a lot of responses to this question since I am as curious as you
are.
> For the actual pole, I used a standard Rohn M200H 10' mast. Is that going
> to be sufficient for 55G, assuming the mount to the tower is O.K.?
Actaully, an M200H is probably overkill for this application. They are kind of
heavy,
being made of steel. Most gin pole masts are aluminum. While I never recommend
aluminum for a permanent tower mast, it seems to be OK for a gin pole if you
carefully
control the sideloading so as to make sure it does not fold over. I HAS
happened . . .
For example, you would generally NOT be using a gin pole on a windy day but your
permanent mast has to stand there and take it everyday. The M200H is also
kind of
short at ten feet. I think the standard Rohn EF2545 pole is 12 feet long, and
made of
aluminum with about 1/8" wall. I used to use that for the "standard" 25 and 45
jobs
without problems but when I wanted to do something more difficult like set a
heavy 20
foot mast, I needed more height for two reasons: 1. I needed to lift a long
load
higher to clear the top of the tower, and 2. I needed more room at the top to
make room
for the double pully of my 3:1 mechanical advantage block and tackle. For
these jobs, I
have a second, 16 foot, 1/4" wall aluminum mast
> Does
> anyone know the yield strength for the M200H?
I think it is something like 50,000 psi but that is not an official answer from
Rohn.
> And how does one rate the
> safe working load of a gin pole anyway?
This is a good question for Hank, KR7X, who really has the qualifications to
answer it.
Just thinking about all of the things that affect the stresses applied to a gin
pole
boggles my mind . . .
> I guess one could calculate the
> breaking point for a perpendicular load at ten feet from the mount. That
> would seem to be worst case. Then apply a 5-to-1 safety factor?
But then there is sideloading from pulling at an angle, wind gusts, and the
inertia of
the load as the pullers jerk on the pull line . . . and more, I am sure.
> One final thing. I used rope in the gin pole for the 45G project, but I'm
> seriously considering using some 1/8" aircraft cable that I have on hand.
> It's quite a bit stronger, and I can fit a lot more of it on the
> hand winch. Anyone see any problems with this?
I see a couple of possible problems. The cable is much smaller than the rope
and
therefore it is much easier to slip off the pully and bind at the pully axle.
This has
happened, too. The use of the winch makes me a little nervous since it is a
little
harder to tell if something is jammed and you are using too much pull on the
cable.
This is why I really dislike power winches and especially vehicles pulling
things up the
tower. A power winch with a capstan drive or an adjustable clutch would
probably be OK.
> 73,
>
> Tim Totten, n4gn@n4gn.com
> http://www.n4gn.com
Just one set of opinions . . . mine.
You have triggered me to put several questions to my contact at Rohn:
1. What is the rating on the EF2545?
2. What do you recommend for a 55G erection fixture?
3. What is the yield strength of the steel used in an M200H?
It remains to be seen what responses I will get but, whatever they are, I will
share
them here. Stay tuned.
Stan
w7ni@easystreet.com
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