[TowerTalk] FW: Hindsight: Check your rotator bolts

[Dan Hearn]

If my memory is correct the original problem occurred when the bolts in the
bottom of a OR2800, holding it to the mounting plate, loosened and fell out.
I believe the rotator holes are tapped blind holes in an aluminum casting. I
think a good solution would be to use bolts with a long threaded portion and
double nuts as suggested. However, I would saw them off at the top of the
thread and saw a screwdriver slot in the top end. These would be turned in
to the full depth of the tapped hole for maximum strength and avoidance of
thread stripping in the casting. I would probably apply a coating of
permanent Locktite to the tapped hole then tighten the dual nuts. Aluminum
has a fairly large coefficient of expansion which might be part of the
loosening problem.
73, Dan, N5AR

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com]On Behalf Of Doug Renwick
Sent: Wednesday, June 11, 2008 8:07 AM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] FW: Hindsight: Check your rotator bolts

Thanks Chuck and George, N4UA, for supplying the correct information.  A
jamnut reduces/prevents the NUTS from creeping.  The nuts do nothing to
reduce/prevent the threaded rod/shaft from loosening over a single nut
similarly applied.

Doug


-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Chuck Lewis
Sent: June 9, 2008 5:18 PM
To: Kimberly Elmore; towertalk at contesting.com
Subject: Re: [TowerTalk] FW: Hindsight: Check your rotator bolts

Wait a minute...

We understand jam nuts. A jamnut prevents the pair of jammed nuts from
moving WITH RESPECT TO THE BOLT or threaded rod; but they don't add any
additional protection against the jamnut/bolt assembly moving in
relation to
the hole the assembly is screwed into. Jamnuts are useful, but not here.

Here's a thought experiment: make up the jammed assembly as described
and
then weld the nuts to each other and to the bolt. Now you have a
permanently
stable assembly of bolt/nut/nut; but this is now absolutely identical in

function to the original bolt, with the jammed and welded nuts being no
more
nor less than the head of the bolt. The rotor base and plate can't tell
the
difference.

Jam nuts are useful on turnbuckles because they act as an "adjustable"
bolt
head, locking the otherwise loose eyebolt against the buckle. They are
also
marginally useful with a stud that's otherwise locked in place and where
the
stud itself is NOT going to loosen within its hole, or where (for other
reasons) it's not advisable to apply sufficient torque to preload the
bolt.
Yes, they depend on applying the correct preload, i.e., stretching the
bolt,
just as a simple bolt, properly torqued. The jamnuts apply preload, too,
but
only in the vicinity of the nuts. The closest nut, or the head of a
simple
bolt still needs (at least) to be torqued to spec.

Jamnuts in this application don't add anything beyond a false sense of
security. Worse yet, if the first nut isn't properly torqued because
it's
thought that the jamnut will substitute, you'll be worse off. Beware of
unintended consequences!

73, Chuck, N4NM


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