Sorry, I note a typo in the article I just posted. Hope this is clearer.
----- Original Message -----
From: "Graham Higgins" <ghiggins@norex.com.au>
Subject: lock nuts
> Dear Ted,
> Thank you for your explanaton. I had drawn the large zigs and zags as you
> suggest. I understand you are refering to the bolt thread in your
discussion
> below.
> It seems to me that the size of the nut does not really matter, because
the
> same problems apply to both full and half nuts, but for the sake of
clarity
> in this discussion I will continue to consider the lock nut as the half
nut.
> You suggest the half nut is applied first, to the correct torque, then
the
> full nut, also to the correct torque.At this point the half nut is just
> about floating, as the pressure on the zig face of the bolt thread is
> approaching zero.As the half nut is backed off, some of the turn will be
> just taking up the slack in the thread, and this does not change anything.
> But as it is backed off further, it is putting pressure on the zag face
of
> the bolt. This must also reduce pressure on the article being held, and
the pressure on the full
> nut threads is increased by the same amount.
> What is unclear to me is whether this reduction is significant, as the
> article being held is under less than the correct pressure.
> The danger of having a floating half nut, thus negating any locking
effect,
> is still present, if it is not backed off far enough to create a definite
> lock on the full nut.
> It seems to me that as the half nut is being backed off, and just starting
> to lock on the zag face, you do not want it to move from that position on
> the bolt . This would require then turning both nuts towards each other ,
> the half nut twice as much as the full nut, to create the lock without
> changing position on the bolt, and maintain the correct pressure on the
> article being held.(If using both full nuts, move them together equally)
> If the thread pressure produced by the required torque to hold the article
> is P1, and the thread pressure produced by the locking action is P2, it
can
> be seen that the outer(full) nut carries P1+ P2, and the inner(half) nut
> carries only P2, which is far preferable to the reverse arrangement having
> the half nut on second,carrying P1+P2.
> The art is judging how firmly to lock the two nuts together!
> Thank you, I now consider myself educated.
> Regards Graham Higgins, in OZ.
>
>
> Hi Kingsley,
>
>
> If you consider a section through the axis of the nut an bolt and greatly
> enlarge the zigzag line formed by cutting through the thread at the
> interface between the nut and bolt, you will see that, when the nut is
> tightened, the pressure will be on the sloping face of the thread towards
> the bolt head - - lets call this the "zig" and there will be a gap on the
> rear facing slope of the thread due to the clearance between nut &
bolt - -
> lets call this the "zag".
>
> If the full size nut is put on first and tightened to the specified torque
> and then the half size nut is put on and tightened, to try and lock it, it
> will tend to push the full nut forward thereby reducing its pressure on
the
> bolts zig face and could eventually force it so far forward that it
reduces
> the pressure to zero and may even produce a gap on the zig face AND zag
> face. The full bolt is then floating free and is acting as nothing more
> than a washer !! In doing so you will invariably have had to apply
> greater torque. The full tension in the bolt is then being taken by the
> half nut - - which it was not designed to carry and could eventually strip
> its threads. There will also be a gap on the zag face which will allow
the
> nut to slacken with any vibration.
>
> If the half nut is put on first and tightened to the correct torque and
> then the full nut is put on and tightened to the correct torque, both nuts
> then have pressure on the zig face, If the full nut is then held
> stationary (to maintain the correct torque and tension in the bolt) and
the
> half nut is backed off (slackened) sufficiently for its pressure to be
> removed from the zig face and transferred to the zag face it will then be
> jammed against the full nut. The full nut will be holding its full
> designed load and be locked by the half nut - - - - just like when you put
> two nuts on a threaded rod and tighten one against the other. There is
> pressure on the zig face of the full nut and pressure on the zag face of
> the half nut thus there is no slackness and vibration will not loosen
them.
>
> ... Ted.
>
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