[UK-CONTEST] rotating guy rings

[g3ory at lineone.net]

Dave,

We have both obviously spent many hours putting up pipe masts; maybe a perverse
kind of mis-spent youth?

There are a couple of points that I could not agree with you:

1. Having the rotator at the top of the pipe mast seriously increases the
head load.  It is not the effort to raise the load that, in my view, is the
problem. It is the fact that if the top of the mast goes a bit out of alignment
at any point, the extra head load make catastrophic failure more likely,
and also gives you less time to try to prevent it happening!
An alternative solution that we at DMUARS have found very successful is to
fabricate a hinged 'cage' for the rotator at the bottom of the mast.  The
rotator is positioned inside the cage. It looks pretty much like a head unit
for a Versatower, except for the hinge on one of the bottom edges.  The bottom
section of the scaf pole mast is inside an 18 inch long sleeve positioned
above the rotator and aligned with it. This prevents excessive side forces
being exerted on the rotator during the erection process. 

2. The problem with external scaffold couplers is that they are too short
for critical applications.  We use them most of the time but when putting
a 20 ft scaf pole as the top mast section with the upper 12 feet unsupported
(to allow for 4 vertically stacked 70cm yagis that must be rotatable through
360 degrees without fouling the guys) we find the 10 bolt coupler to be best
because it makes for a more rigid join.  Naturally the 10 bolt coupler must
close up on 1 29/32 inch scaf, but all of ours seem to this without problems.

73

Bob
G3ORY

>-- Original Message --
>Date: Mon, 14 Feb 2005 23:01:39 +0000
>From: Dave Lawley <g4buo at compuserve.com>
>To: UK Contest Reflector <uk-contest at contesting.com>
>Subject: Re: [UK-CONTEST] rotating guy rings
>
>
>Hi Steve
>
>To make our poles easier to rotate (armstrong method) on VHF FD we use a
>
>steel ring above the scaffold clamp, then a PTFE ring, then on top of 
>that the 6 inch square plate carrying the guys.
>
>However, there can be quite a lot of friction and you could be stressing
>
>the rotator quite a bit. It will be important to get the mast as 
>straight as you possibly can, which may mean turnbuckles at the guy 
>stakes for fine adjustment. If the wind blows hard, there will be more 
>friction.
>
>Putting the rotator at the bottom of a fixed lattice tower can be a good
>
>idea for maintenance purposes and to take out some of the torque due to

>windage on the antennas. But for a 50ft scaffold mast erected from time

>to time I reckon the best place for the rotator is up top.
>
>For G1A last October I put up a 3el tribander plus G600 rotator at 50ft

>on a sloping site single-handed. The key is to use a sufficiently long 
>gin pole (I used 18ft made of two 9ft scaffold tubes) and a block and 
>tackle. I used two 2-blocks, with the right size rope for the sheaves, 
>important to minimise friction. The other thing to remember is to make 
>the top guy to the gin much tighter than the others, this puts an upward
>
>bend in the mast which compensates for the extra weight at the top.
>
>While I'm on the subject, be very wary of the J-beam scaffold couplers.

>Some of them don't do up tightly enough around a scaffold pole which as

>you may know is not 2inch diameter but something like 1 29/32 inch. We 
>always use external scaffold couplers which are only half the length but
>
>much stronger.
>
>Dave G4BUO
>
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