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[TowerTalk] Water pipe

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Subject: [TowerTalk] Water pipe
From: (Lee Buller)
Date: Tue, 11 Nov 1997 04:22:29 -0600
At 09:50 AM 11/11/97 +200, you wrote:
>K0WA wrote:
>> The issue I have with this senario is drilling the mast.  I have done
>> this in the past, but if I had my druthers, I would never... 
>> never... never pin a mast if I could help it.  I don't care how 
>> tight you drill the hole, or how hard the bolts are...the wind 
>> moving the beam around will wallow out the holes and the whole 
>> thing will get loosy goosy.  Once you get a degree of arc (slop) 
>> in the mast, you will take out your very expensive rotor. Just a
>> warning...cause it has happened to me.
>Two points:
>1.  Any idea what would have happened under these conditions if the
>    mast was not pinned?  I would think that the kind of torque
>    that could cause this much play would have allowed the mast
>    to turn in the rotator, necessitating several trips up the tower
>    during the lifetime of the system.  Maybe those same trips could
>    have been used to do some routine maintenance instead.
>2.  Following healthy engineering practice and using a pair of thrust
>    bearings above the rotator would remove anything but torque from
>    the rotator.  That being the case, I cannot see how the mast 
>    could damage the rotator if there is play in the mast.
>Chris R. Burger


With all due respect, I do not see how a pair of thrust bearings are going
to help when you pin a mast.  The metal will fatigue around the hole.  If
you use something like water pipe (galvanized) you can count on a drilled
hole wallowing out from the torque action of the beam blowing in the wind
and the brake in the rotor.  Usually the bolt is much harder than the pipe,
therefore as the mast turns (even when you are turning it) there is friction
and rubbing between the bolt and the pipe.  Sooner or later, the hole will
be much larger than the bolt.  Galvanized water pipe is somewhat soft.  Now,
all bets are off with Chrome-Molley, but I wouldn't do it even then.  Wind
forces, turning the beam and miss drilling the hole will cause the hole to
wallow out.

You can loose a brake in the rotor. Lets say you have a quarter of an inch
of plan in your mast because of your pin.  It is wallowed out.  That quarter
of an inch projects to several feet at the end of a beam's boom.  The wind
starts whipping around the boom trying to find an aerodynamically stable
place (and the wind changes direction a lot) and you have a lot of torque on
the rotor.  It would be like putting a cheater bar on a wrench.  You can
break the wrench  

I have seen triple case harden and schedule 8 bolts sheared off, and I have
seem mast where the holes are oblong and not round.

Another observation, if you do this...make sure that you do not expose any
thread of the bolt to the pipe.  Use a precise shoulder bolt with a lock
washer.  I would double nut the thing myself.  If you expose the threads to
the hole, then the hold is much bigger than the bolt, because the threads
are slightly smaller in diameter.  Therefore, you start the process.

If you have to do this, have a machine shop actually do the work and get it
precise.  IT will last longer that way, but it will have to be replaced in
the long run.

I learned that you need one continuous mast.  I don't want anything turning
up there with out the help of the rotor.  IT has to be rock
slop... or you will replace a rotor.  



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