wrote:

There are several all-steel locknuts avalable from aircraft
parts places, or even from the average aircraft repair shop. They're
used in hot areas like the engine compartment, or in areas where the
manufacturer has reason to specify them. One popular type looks a bit
like a castellated nut but the slots are very narrow and the top end is
crushed just enough to give good friction. The threads run all the way
through. Their friction is higher than the nylock, and the thread fit
is class 2, much better than the average cheapnut. There must be ten or
fifteen neat locknut types for just about any oddball application.
Check yer Yellow Pages under Aircraft Parts or Aircraft Repair.
See http://www.aircraftspruce.com/menus/ha/nuts.html and scroll
down to All Metal Stop Nuts.

Just for the record, I spent a good deal of the taxpayer's money resolving a
problem involving elastic stop nuts on a military aircraft a while back.
The following is based on that experience--it's not my uninformed opinion.

Nylon insert elastic stop nuts are typically rated for 50 reuse cycles. If
the threads are clean and not burred, they'll do a few more than that
before the torque drops below the value required by the specifications--how
many more depends on the finish quality of the bolt, whether it has a dry
film lubricant coating, how clean it is, and other factors which we were
never able to identify.

If the threads are burred or have abrasive material on them then the torque
can go below spec in a single cycle.

There is a temptation to use all metal elastic stop nuts on the basis that
they are more "durable". They aren't--I was specifically told by my
supervisor to consider an all metal nut and I found out that they are not
rated to last nearly as many cycles as Nylon, and they don't--their primary
utility is for high temperature areas where nylon would melt.

If you want _real_ durability there are nuts with a Vespel (chemically
related to Kevlar) insert that are rated for 500 cycles, and we had a guy
in the lab to run a bolt in and out of a bunch of those things 500 times
with a torque wrench, to confirm that they really worked as
advertised--they do. But a burr on the fastener can still take out the
insert quickly.



Dan

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)