Thanks to those who responded to my previous post.
Some good ideas.
HOWEVER - it appears I phrased my question wrongly
and it never got answered. It is this:
Can/should lock washers be reused?
I'm referring to the simple split lock.
Once the screw is tightened down, and you then remove the screw - will the
lock still be effective on retightening? MY guess it that it should last for
a number of loosen/tighten cycles and eventually loose it's spring and THEN
need to be replaced. Just looking for a confirmation of this thinking.
It depends on the situation. If your application requires the nut to be
tightened to, say, 1000 foot pounds, you probably shouldn't reuse the lock
washer. On the other hand, if your nut is only hand tight, then go ahead
and reuse the washer.
I'd just compare the uncompressed height of a "used" one with an unused
one. If it's about the same, I wouldn't worry about it. Replacing the
lock washer every time you change the knife blade would be an extreme
case of "gilding a turd".
I can't recall anywhere I've read instructions saying to replace
lockwashers when reassembling something. They're not in the same
category as those one use "stretchable" engine head bolts. But, it
wouldn't suprise me that critical applications like aircraft stuff might
just call for that.
Yes, we are not supposed to reuse lock washers. Also, lockwashers are rarely
used in aircraft, they mainly appear in non-critical uses. The most critical
bolts are wired in place.
There are other rules as well. I got a nice lecture from my A&P once when
I told him I could clean up a stripped nut with a tap and die set. Apparently
no threads are ever cut on an aircraft, it produces a weaker thread.
On Sat, 19 Jun 2004 07:37:12 -0400, Alan Reinhart
vaguely proposed a theory
......and in reply I say!:
remove ns from my header address to reply via email
In theory, a _well made_ lock washer should maintain its spring.
Having said that if you overtighten the nut onto the washer, you can
get spread of the washer, and that can be not good. Usually lock
washers, IME are used when the torsion is not used to hold the
nut/bolt, but you simply tighten and let the washer do the work. lock
washers are rarely used again IME in torqued situations.
If the washer still has a "coil" to it, then it has maintained its
spring and will still hold against the nut.
I doubt if a lock washer will ever lose its spring regardless of how
high the torque is on the bolt. It might lose the sharp edge that
digs into the bolt head and the metal, and it might fatigue and break.
I reuse them mont of the time, but will replace them if I think it is
important that the bolt does not loosen. Or if the bolt has actually
- will the
Since no one has mentioned it yet, here's what Carroll Smith has to
say in "Screw to Win" ISBN 0-87938-406-9.
"Neither the spring washer nor the wave washer do anything worth
talking about - other than to provide the user with a false sense of
security. Think about it for a moment. From experience, you know that
it takes very little load to compress a spring washer. For example,
the spring washer will be completely closed long before we reach
recommended torque when tightening a bolt. Once compressed, the spring
washer is nothing but a flat washer. If, for whatever reason, a bolt
should loosen to the point where the spring washer opens enough to
become a spring, there was too little residual stress in the assembled
bolt for any sort of safety. in other words, the thing wasn't
tightened sufficiently. Exactly the same is true of the wave washer
which is , for some reason or other, is popular in Germany. If you
decide to use a spring lock washer, a flat washer should be placed
between the lock washer and the work surface to prevent damage to the
surface. This is not necessary with the wave washer.
I am willing to admit that there are installations where the serrated
or star washer can be effective. These installations are limited to
the smaller sizes and almost always have to do with machine screws
baring on a relatiely soft surface - aluminum or plastic, for example.
The teeth of the washer can and do bite into the surfaces of soft
materials and offer reasonably positive protection against rotation.
They are available with either internal or external teeth, and also as
coned washers for countersunk bolts.
I try not to use lock washers. I use prevailing torque-type
self-locking nuts on all through holes, and check or jam nuts to lock
rod end bearings and threaded adjusters. With blind holes, if I do not
trust the thread tension of a properly tightened bolt, I use the
appropriate grade of Loctite and /or safety wire. I do, however, carry
a selection of aircraft spec (AN-935) spring lock washers around with
me - just in case. I will not use industrial spring lock washers
because they are liable to be too brittle for my taste."
I don't think any kind of lock washer is going to help in your
situation. Aluminum or zinc based alloys are very bad when you have to
regularly remove and refit fasteners. These materials are almost
guaranteed to gall at some point no matter how carefully they are
assmembled. The best approach would be to Helicoil or use some other
type of threaded insert.
It would also be a good idea to switch to a hex head or internal
wrenching (Allen) bolt. The tool used for fastening should be of the
screwdriver type not a ratchet or wrench.
For *external* threads!!
For internal threads a die does not cause a problem, even under
high stress applications. This is because the female thread
is invariably in a larger piece of material.
Besides, I don't think they ever do roll inside threads.
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
Different animal. Forming taps do not orient the
grain structure the way it happens on rolled thread
bolts. You would not see the same benefits.
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
||> Can/should lock washers be reused?
||> I'm referring to the simple split lock.
||> Once the screw is tightened down, and you then remove the screw - will the
||> lock still be effective on retightening? MY guess it that it should last for
||> a number of loosen/tighten cycles and eventually loose it's spring and THEN
||> need to be replaced. Just looking for a confirmation of this thinking.
I'd be looking at replacing the screws with studs, and retaining the blade with
a nylok nut.
Texas Parts Guy
A little off base but....... Once upon a time I was replacing a half shaft on
a front wheel drive Ford product. Not being an expert I read all the manuals I
could on the procedure. The books said "CAUTION: Don't reuse the pinch bolts
and nuts that hold the ball joints in place". I tried four Ford dealers parts
departments before I found one that had them. The dealer that had them was
located in a small town.
What does that tell you?