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
----- Original Message -----
From: "Kimberly Elmore" <cw_de_n5op@sbcglobal.net>
To: <towertalk@contesting.com>
Sent: Monday, June 09, 2008 4:45 PM
Subject: Re: [TowerTalk] FW: Hindsight: Check your rotator bolts
> Jam nuts are pretty common devices and are used all the time in things
> like turnbuckles. Here's a simple test: tighten one nut against another on
> some threaded rod, screw or bolt. Then, try to turn them. You can't. The
> method depends on the elasticity of the threaded rod material: you have
> essentially stretched the threaded rod between the two nuts. As long as
> the stretched material doesn't permanently distort, the tension remains
> and friction between the threads of the nuts against the threaded rod
> holds the two nuts immobile.
>
> Kim Elmore, N5OP
>
> ----- Original Message ----
> From: "Dubovsky, George" <George.Dubovsky@andrew.com>
> To: towertalk@contesting.com
> Sent: Monday, June 9, 2008 2:23:37 PM
> Subject: [TowerTalk] FW: Hindsight: Check your rotator bolts
>
>
>
> -----Original Message-----
> From: Dubovsky, George
> Sent: Monday, June 09, 2008 2:48 PM
> To: 'Roger (K8RI)'
> Subject: RE: [TowerTalk] Hindsight: Check your rotator bolts
>
>
>
>> -----Original Message-----
>> From: towertalk-bounces@contesting.com [mailto:towertalk-
>> bounces@contesting.com] On Behalf Of Roger (K8RI)
>> Sent: Monday, June 09, 2008 2:04 PM
>> To: Tower Talk
>> Subject: Re: [TowerTalk] Hindsight: Check your rotator bolts
>>
>> Dubovsky, George wrote:
>> >
>> >
>> > If you think about it, this accomplishes nothing that a bolt would
> not
>> > accomplish in the same application.
>>
>> Yes it does.
>
> No, it doesn't. So, there... ;-) My bolt has exactly the same holding
> force on the lockwasher/captive plate as your double nut scheme does.
> You claim the second nut keeps the first nut from loosening; the head of
> my bolt never changes its orientation to the threaded section, so it
> never "loosens" either. If my bolt loosens from vibration, so does your
> scheme. Check your mechanics again.
>
>> > The second nut does nothing more
>> > than make the first nut "thicker".
>> A thicker nut and two nuts "locked" or jammed together are quite
>> different in the way they work.
>> A thicker nut or rather one twice as thick (two nuts) offers twice the
>> area as do two nuts, but the two nuts work against each other by
>> preventing each other from turning. The thicker nut does not.
>> > If a properly sized bolt with a good
>> > lockwasher under the head is not going to hold, than neither is an
>> > improperly sized (long) bolt with two nuts forming a new "head"
> further
>> > down the shank of the bolt.
>> The mechanics of the two are quite different as is the purpose. The
>> problem is not holding, the problem is the bolt coming loose.
>> Again two different problems although if a bolt comes loose it won't
>> hold, not holding doesn't necessarily mean coming loose. IOW the one
>> can break where the other just vibrates loose.
>> > The second nut only guarantees that your new
>> > "bolt head" doesn't move on the threads of the bolt, but the head on
> a
>> > hex-head cap screw already has that feature manufactured in.
>> >
>> >
>> Both serve as "heads", but only one serves as a lock.
>> The "jam nut" is not nearly as simple as it sounds.
>>
>>
>> Roger (K8RI - ARRL Life Member)
>> www.rogerhalstead.com
>> N833R (World's oldest Debonair)
>>
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
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>> TowerTalk@contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>
>
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