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Re: [TowerTalk] Mast slipping

To: <K7LXC@aol.com>, <towertalk@contesting.com>,<alwilliams@olywa.net>
Subject: Re: [TowerTalk] Mast slipping
From: "Keith Dutson" <kdutson@sbcglobal.net>
Date: Sun, 22 Apr 2007 17:21:11 -0500
List-post: <mailto:towertalk@contesting.com>
Ya'll have me wondering about my 40M tower plan.  Last fall I took delivery
of two M2 40M4LLDD Yagis.  This antenna has 4 elements on a 42 foot boom,
but a surprisingly sparse 13 square feet windload rating.  They will be
mounted at 100 and 200 feet on a 190 foot Rohn 55G tower.  The top antenna
will be rotated by an Orion 2800 that was purchased at the same time.  The
lower will be rotated by a TIC Ring.

This tower was supposed to be going up this spring but unexpected surgery
has delayed the project for a year.

After hearing about all of the mast slipping problems I decided to take the
Orion out of its box and have a look.  According to the instructions, the
"positioner" has been recently improved and strengthened.  Since I do not
have an older unit, I have no way of knowing what is improved or how much
stronger it is.  Here are some specs:

wind area               35 sq ft
start torque    4200 in lb
rotating torque 3200 in lb
braking torque  17000 in lbs
vert load cap   1800 lbs

I took a photo of the mast clamp halves (see below).  Interestingly, there
is a hole in each that is sized to take a 1/4 inch bolt.  This could
certainly be used to pin the mast but leaves doubt about the strength to
hold it.

http://www.dutson.net/Transfer/HamRadio/Orion2800Clampds.JPG

73, Keith NM5G

-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of K7LXC@aol.com
Sent: Sunday, April 22, 2007 12:04 PM
To: towertalk@contesting.com; alwilliams@olywa.net
Subject: Re: [TowerTalk] Mast slipping

 
In a message dated 4/22/2007 8:43:23 A.M. Pacific Daylight Time,
towertalk-request@contesting.com writes:

>  About a year ago I had a conversation with the m2 people  about their
rotator
clamp slipping on my Monstr's mast.  What follows  is my memory of the
conversation:

>  1. It is better to  have the clamp slip than to harm the rotator.  (Note:

the
wind  banging repeatedly on the gearing can weaken the gears?)

>  2.  The specified braking torque has not been measured (or  calculated?).

>  3. Pinning voids the warranty.  I would  assume that using a 
> different
mfrs
clamp would also void the  warranty.

>  4. They recommended a clamp bolt tightening  sequence that should be
followed.  Unfortunately I wasn't able to get  a firm answer on what torque
to tighten the nuts to.  The sequence to  follow is:

>  a) bolt the rotator to the mounting plate but  leave the bolt/nuts 
> not
tightened
b) with the bolts to holding  the rotator to the mounting plate loose,
tighten the bolt/nut pair of the  clamp that is nearest the bottom.
c) tighten the next (middle)  bolt/nut pair of the clamp
d) tighten the top bolt/nut pair of the  clamp
e) repeat steps b,c,d several times
f) now lastly,  tighten the bolt/nuts of step a

>  I did get an answer of 40  ft/lbs from the m2 person but I think that 
> was
just pulled out of the  air.
 
    Very interesting but not useful. It doesn't do  anything about the
significant design flaws of the Orion mast clamp that ARE  the problems.
None of the above will keep the mast from slipping. 
 
Cheers,
Steve      K7LXC
TOWER TECH 



 



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