A while back, there was quite a fastener thread in this segment.

Not trying to start any wars, but I just ran across an article in the July 2004 SuperRod. Author's name is Wayne Scraba.

Article references aircraft fasteners and FAA requirements. Where it gets interesting is the point about standard nuts. It states that if these are used with lockwashers, a standard washer should be used under it to protect the surface.

There was quite a lot of opinion on the former thread that lockwashers with standard washers were not effective.

Just interested in any opinions.

ford2go

 

With aluminum or plastic, use a standard washer under the lock washer, or just use a nyloc nut. On steel, you can use the lock washer without the standard washer.
I'd use caution in applying aircraft standards in automotive applications.

 

Jared is correct. On aluminum, plastic, wood, soft materials, etc a protective washer must be used to spread the load and protect the surface but a standard lockwasher is ineffective in that application. Other types of locking fasteners must be used like nylocks or distressed thread locknuts or even special bolts with interference threads. There are a lot of options.

 

This is probably more than you'd ever want to know about lockwashers but good information never the less. The following is from the NASA publication "NASA Fastener Design Manual":

Lockwashers

The typical helical spring washer is made of slightly trapezoidal wire formed into a helix of one coil so that the free height is approximately twice the thickness of the washer cross section. They are usually made of hardened carbon steel, but they are also available in aluminum, silicon, bronze, phosphor-bronze, stainless steel, and K-Monel.
The lockwasher serves as a spring while the bolt is being tightened. However, the washer is normally flat by the time the bolt is fully torqued. At this time it is equivalent to a solid flat washer, and its locking ability is nonexistent. In summary, a lockwasher of this type is useless for locking.

Tooth (or Star) Lockwashers

Tooth lockwashers (fig. 15) are used with screws and nuts for some spring action but mostly for locking action. The teeth are formed in a twisted configuration with sharp edges. One edge bites into the bolthead (or nut) while the other edge bites into the mating surface. Although this washer does provide some locking action, it damages the mating surfaces. These scratches can cause crack formation in highly stressed fasteners, in mating parts, or both, as well as increased corrosion susceptibility.

Personally, I've just about stopped using lockwashers for anything. However, I do use Loctite on almost everything. The self-wicking type can be used on assembled fasteners and works fairly well. In addition, they now have surface insensitive grades that don't require the use of a primer. A little expensive, but I've never had a fastener assembled with Loctite come apart.

 

IMO aircraft standards are much higher than automotive.

If you want to make sure a fastener is not going anywhere use safety wire!

 

I agree. Safety wire is probably the ultimate insurance against vibration. However, the design of the component must take into account the use of safety wire. A lone fastener securing a bracket is difficult, but not impossible to safety wire. In addition, there is a practical lower limit to the size of a fastener that can be safety wired. Anything smaller than 1/4 inch would be tough to wire. Also, I don't recommend drilling your own bolts for safety wire unless you can be certain that the hole will be in exactly the right place so that it doesn't compromise the strength of the fastener.

Safety wire has its place. Aircraft, race cars, high vibration highly stressed machinery, etc. Loctite is so much easier and can be used on ANY threaded component not subjected to extreme heat.

 

If an assembly is correctly designed, and the bolts that hold it together are properly torqued, there is very little chance that a bolt will back out. When the bolt is torqued it is being slightly stretched. What keeps it tight is the friction between the bolt head and the part and the friction of the thread. If the friction surface is small and it is subjected to a lot of stress and vibration it can come unscrewed. You can increase the friction surface area by using washers which will more than double the contact. Like a double disk clutch.

I'm not buying the NASA analysis of the lock washer. They have their place, especially when the componants being bolted together have any considerable expansion/contraction factor to deal with. If the material is soft, you may need a large bolt for the load it is subjected to, but you can't apply enough torque to stretch the bolt. In that case, a regular lock washer will keep enough pressure on the nut to prevent it from turning.

 

I don't buy the NASA info either. That statement is not correct. A properly formed lockwasher is not "flat" at all. The points on a properly formed split section are forced by spring pressure, the stress produced by the fastener torque, and the shape of the edge of that section into the surfaces of the adjoining metal surfaces. They gouge a hell of a groove in the parts when removed. I have seen a number of improperly formed lockwashers on the shelf tho. A properly formed lockwasher is a hell of a stress riser tho... Probably why they are used on heavy machinery where weight and thickness are not figured down to the last hundredth of a gram or MM tho.

I use many different kinds of locking mechanisms based on the application and the reliability needed.

 

There's probably some truth in what both of you are saying. However there is also quite a bit of truth in the NASA analysis as well. Consider this:


If a lock washer, of any type, does actually "lock" the fastener to the assembly then wouldn't you need one under the head of the bolt AND the nut? What good would it do to lock only one component? Of course this doesn't apply to a threaded hole.

If you use a flat washer under the bolt head or the nut in order to spread the clamping force over a larger area where does the lockwasher go? If it goes between the washer and the assembly, the bolt head is free to turn on the washer. If it goes between the bolt head and the washer you've simply created a bolt with a larger head. Would you use 2 lockwashers?

As far as tearing up the surface, yes the lockwasher will do that as it is being tightened while there is still an offset between the ends. Once properly tightened, it is essentially a flat washer, although it is now a flat washer resting between two surfaces with burrs on them.

A properly torqued fastener stays tight by virtue of both the fastener's stretch providing a clamping force on the assembly and friction between the thread flanks.

Lockwashers have their place. Both Bdox and Torque 1st are right. But so is NASA. The bottom line is that it all depends on the application. Lockwashers are fine under small fasteners holding non critical parts in low vibration areas. You rarely find them in high vibration, highly stressed applications. There are just too many other, better solutions.

 

Lockwashers are only used under the nut. Usually the parts clamped together hold the shank of the bolt in a "bind" that prevents the bolt from turning.

A properly formed lockwasher will not tear excessively into the surface when tightened. The points slide over the surface when tightening. Unless of course there are left hand threads involved with right hand lockwashers, a real mess (but I have seen it done -hehe). The points will only penetrate the surface during the last few degrees of rotation with right hand threads and standard RH lockwashers. The lockwasher is never a "flat" washer. Lockwashers are also used in high vibration environments. In critical applications they are also combined with Loctite and other locking methods. In critical aerospace applications I would not use them due to the stress risers they produce. Every application must be carefully analyzed. We are talking about automotive applications at FTE tho. I suppose aerospace forums exist for discussions related to aerospace fastener technology.

For most automotive frame and general bolting applications I would not hesitate to use them. I have observed many situations over the years both in automotive and industrial machines where identical assemblies were assembled with and without lockwashers. The assemblies that were just torqued without lockwashers failed while the assemblies with lockwashers held together. The lockwashers made the difference. The difference was night and day. I have also seen the 100% failures from people adding a flat washer under the lockwasher.

Assemblies where Loctite was used also failed due to the fact that fasteners were not properly cleaned and prepped for the sealant. When fasteners were properly cleaned and prepped Loctite was very good. Unfortunately most shade tree mechanics do not clean and prep the fasteners properly making Loctite useless. I have watched many mechanics add a drop of regular red or blue Loctite to a greasy or oily bolt and install it. I have also watched while someone tapped a hole on a machine using tapping oil then selected an oily SHCS from a bin, drop a drop of Loctite on it, and then install it with a torque wrench expecting it to hold...

Remember, most lockwashers purchased at the local store are cheap China imports and not properly made. Real lockwashers can be purchased from industrial fastener companies. Their bargain brand is likely to be a cheap useless China import also so any lockwasher must be inspected and examined closely. Most companies unfortunately do not have much of an inspection department and buy only on "price".

BTW- Conventional flat washers are too soft and thin to spread the load under a highly stressed fastener. They work OK on soft materials with lightly stressed fasteners. Hardened and ground, SAE, or machinery washers are much thicker and also smaller in diameter and can be used to help spread the load with harder materials, but never with a lockwasher next to them...

 

My personal favorite method of keeping a nut tight is to double nut. I've never had one come loose doing this. I always torque the first nut then hold the first while I tighten the second one to the first.

Of course this doesn't work when the nut is hidden or the bolt isn't long enough but that is seldom the case.

 

Double nuts work excellent!!!

 

I've always wondered if the use of anti-seize lube on the threads negates the gripping of the nylon part of a nylock nut.

I haven't heard convincingly one way or the other.

 

I don't think it does to a measurable effect-
When working in the shipyard, Nyloc nuts were installed with anti-seize, while non-nylocs and damaged nylocs were installed with locktite blue.
This was for direct saltwater contact on a sub, on Nicu bolts.

 

I agree with Ford_Six on the grip issue. But using anything - anti-seize, Locktite, etc. will have a significant effect on the proper torque value for the fastener. In most cases, the torque value specified for a particular fastener is for "clean, dry threads". Most anti-seize compounds have an oil or grease base. In some cases you have to decrease the applied torque by up to 40 percent.