Message text written by INTERNET:europa-list@matronics.com
>
>- - - - - - - - ->
> 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
|