On 2013-12-20 08:55, Patrick Greenlee wrote:
Interesting dialog about slipping mast, antenna, and rotator clamps.
What is wrong with a sheer bolt? (through bolt in sheer)
Patrick NJ5G
My big mower comes with a sheer bolt. The concept is
that the sheer bolt MUST be a relatively soft materical
and the shaft assembly must be a relatively hard material.
The sheer bolt is designed to break off if you hit
a stump, etc. It also gets gradually chewed up due
to normal wear and tear and eventually breaks apart
for no particular reason. The warranty is void if
you replace the sheer bolt with a grade 5 or something
hard. My neighbor performed that experiment and broke
his gear box.
If you want to replicate that on your tower, then you
immediately have the problem that your mast is not
hardened (and if you have an aluminum mast forget it).
It you do get it to work, then whenever there is a
sufficiently big storm, the sheer bolt saves your rotor,
but the cables get trashed. You get to climb the
tower and fix all this stuff, but at least the rotor
doesn't break.
If you replace the sheer bolt with a grade 5 or 8, then
it gradually enlarges the hole in the soft mast, with
produces more play, which exascerbates the problem.
And you no longer have a mechanical fuse, so you better
have a really rugged rotor.
What you really need to do is to do some precision
drilling and tapping so that the bolt is threaded
into both the mast and the mast clamp so there is
zero play. Unfortunately, this makes it very difficult
to line up the holes to get the bolt threaded in,
with the antenna flopping around making the mast
turn.
So in conclusion, pinning the mast is not a panacea,
but has its own problems.
Rick N6RK
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