Reusing Lock washers II

I would agree with you on this, unless it's a more critical application involving safety or vibration.

RJ

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.

Jeff

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 loosened.

Dan

- will the

Its not so much as loosing the spring of the washer as loosing the cutting edge that digs into the nut... Once you remove the nut you are rounding off the sharp edge of the washer...

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."

Kelley's comments:

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.

Cheers,

Kelley

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.

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

Just in case he needs a false sense of security? Lots of stuff I agree with in what I snipped out, but I think this guy needs a better editor.

Ned Simmons

Sure they do.

Forming taps.

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.

Jim

================================================== 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

I think you do get some of the same benefits when you use forming taps. But internal threads usually are not the ones that fail from stress.

Dan

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?

That Ford halfshafts never fail (:

People in small towns don't replace halfshafts?

No! They don't bother to fix Fords. Gerry :-)} London, Canada