OK! My little experiment was valid, but I agree that it was the wrong
experiment! I have turned around to becoming completely convinced, after
doing some more thought experiments. Ted has accurately portrayed the
situation, and I hope that we don't have to beat on this any more!
Pops
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Chuck Popenoe
Subject: RE: Europa-List: lock nuts
I've been following this thread and haven't been convinced by the arguments.
So, as an curious experimental scientist, I happen to have in my lab a
Skidmore-Wilhelm tensile test device, capable of measuring the tensile load
on a bolt quite accurately. I placed a 1/2-13 bolt in the device and with a
fitting nut, torqued it to 6000 lbf measured tensile force. I then placed
another 1/2" nut on top and torqued it down as a locknut. The tensile force
on the bolt did not change--remained at 6000 lbf. Next, I loosened the
locknut and tightened it to snug condition, and while holding the locknut
fixed, backed off the lower nut to lock the pair. The bolt tensile preload
decreased to 5000 lbf. I repeated the set of experiments again, with the
same result. Q.E.D.! This little experiment confirmed my suspicions that
the locking nut should remain on top. Please tell me if am I doing
something wrong?
Pops
A036 -- on hold at the moment.
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Edward
Gladstone
Subject: Europa-List: lock nuts
--> <Ted_Gladstone@compuserve.com>
Message text written by INTERNET:europa-list@matronics.com
--> <ghiggins@norex.com.au>
>
>- - - - - - - - ->
> 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,
> - - - - - - - - ->
>
Hi Graham,
When you apply the correct torque to the nut you are actually stretching the
bolt to provide the correct design tension in the bolt ( it is actually
amazing just how much stretch occurs in the bolt - - - try taking a 4 or 5M
bolt of about 2 & 1/2" long, slide a 2" thick wall tube or a stack of
larger nuts or washers over it, finger tighten a nut down on it and measure
the length of the bolt with a vernier (or preferably digital)
caliper. Then tighten the nut with a spanner and measure the length of
the bolt again - - you will be surprised by how much it has stretched !!)
Thus, when you back off the half thickness nut to apply pressure against
the full nut, although you increase the pressure on the zig face of the
full nut, as long as the full nut has not turned, the stretch in the
bolt, and therefore the tension in the bolt will not have changed. The
article will still be held at the correct pressure.
Ted
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