Proper use of star washers.

Shepherd

Shepherd

Final Approach
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Shepherd
Someone scolded me today for not using a flat washer under a star washer.
Comments, please.
 
Doesnt seem right but Im a dumb.
On old cars star washers are used to dig and bite into what they are against and not spin such as painted body parts or a few aluminium pieces. Putting a flat washer under it makes no sense to me.
 
Shepherd said:
Someone scolded me today for not using a flat washer under a star washer.
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Standard practice to use flat washer with lock washers of any type especially when the underlying surface is a soft material. It's stated in most guidance: AC43.13, Standard Aircraft Handbook, etc. FYI: star washers are intended as a one-use item whereas split lock washer maybe used multiple times if retain locking quality.
 
Robert Gee said:
Doesnt seem right but Im a dumb.
On old cars star washers are used to dig and bite into what they are against and not spin such as painted body parts or a few aluminium pieces. Putting a flat washer under it makes no sense to me.
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This is a common misconception about how lock washers function. They aren’t designed to “dig in” in order to prevent rotation. They are designed to apply a spring load on the fastener to prevent rotation.
 
In days of yore, I was told if you were using the star washer against a thick part or steel, you didn't need a flat washer, but against thin aluminum you put a flat washer between the star washer and the thin aluminum.
But this was back in prehistoric times.
 
Grum.Man said:
This is a common misconception about how lock washers function. They aren’t designed to “dig in” in order to prevent rotation. They are designed to apply a spring load on the fastener to prevent rotation.
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Spring washers, sometimes called wave washers, are designed that way so there is no need for a flat washer but split lock washers and star washers do indeed have a sharp tang edge that will dig in and mar the surface especially upon removal. The flat washer is simply a sacrificial surface to prevent this from occurring to the surface of the structure that is being secured, especially if it is aluminum.
 
Silvaire said:
Spring washers, sometimes called wave washers, are designed that way so there is no need for a flat washer but split lock washers and star washers do indeed have a sharp tang edge that will dig in and mar the surface especially upon removal. The flat washer is simply a sacrificial surface to prevent this from occurring to the surface of the structure that is being secured, especially if it is aluminum.
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You are correct, but that digging isn’t what creates the “lock” which is why you use a washer between the surface and hardware. If the digging was doing the locking, the washer would negate them.
 
Grum.Man said:
This is a common misconception about how lock washers function. They aren’t designed to “dig in” in order to prevent rotation. They are designed to apply a spring load on the fastener to prevent rotation.
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'K then, if star washers aren't made to dig in, 'splain me why they are used between the lugs of a thermocouple connector for, say, a JPI, rather than under the screw?
 
Chip Sylverne said:
'K then, if star washers aren't made to dig in, 'splain me why they are used between the lugs of a thermocouple connector for, say, a JPI, rather than under the screw?
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Not familiar with that application, have a picture?

Edit: never mind, found an installation manual online. I could speculate several probably reasons but at the end of the day it’s the spring action of the star washer keeping the nut and bolt together not the teeth biting. There could be positives to having the teeth, of course they will dig in which probably makes a better electrical connection. They could be using it as a spacer so that one ring doesn’t hit the insulation of the other. And of course it could help keep the rings from spinning or deforming while tightening.
 
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Grum.Man said:
Not familiar with that application, have a picture?

Edit: never mind, found an installation manual online. I could speculate several probably reasons but at the end of the day it’s the spring action of the star washer keeping the nut and bolt together not the teeth biting. There could be positives to having the teeth, of course they will dig in which probably makes a better electrical connection. They could be using it as a spacer so that one ring doesn’t hit the insulation of the other. And of course it could help keep the rings from spinning or deforming while tightening.
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Couldn't find a pic, but the following is lifted directly from the IM:

"Place a ¼ x 4 inch sleeve over each pair of wires in the wiring. Connect the wire ring lug to the probe ring lug using the supplied number 4 screws and nuts, placing the star washer between the ring lugs, not against the nut."
 
Grum.Man said:
There could be positives to having the teeth, of course they will dig in which probably makes a better electrical connection.
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And that's it. Sometimes they're found between crimp terminals and whatever they're screwed to, for that reason.
 
They really work where vibration is present. Spruce sells them. Not cheap but reusable so you don’t need many.
 
Grum.Man said:
This is a common misconception about how lock washers function. They aren’t designed to “dig in” in order to prevent rotation. They are designed to apply a spring load on the fastener to prevent rotation.
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Makes plenty of sense. I guess not being taught by a book I was told to use them not to keep the bolt from backing out but so the washer wouldnt spin as its being tightened.
So why use a star washer and not a split washer, other than the manual says? ...and is that an inside star or outer? JK!:eek:
 
Robert Gee said:
Makes plenty of sense. I guess not being taught by a book I was told to use them not to keep the bolt from backing out but so the washer wouldnt spin as its being tightened.
So why use a star washer and not a split washer, other than the manual says? ...and is that an inside star or outer? JK!:eek:
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They are typically interchangeable. A split washer is thicker so may not work on some applications. Split washers are also more expensive.
 
Stewartb said:
These are particularly good under exhaust nuts on Lycomings. No more loose nuts or studs.

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My logic sensor is failing on that one. If the Edges of the washer are good enough to prevent spin then the “ramp” is not needed in the first place. If they aren’t good enough to prevent spin, then how is the ramp making any difference at all.
 
Chip Sylverne said:
why they are used between the lugs of a thermocouple connector
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FYI: you’ll find different applications (industries) use standard parts for different reasons. Existing guidance for the use of lock washers in securing aviation mount hardware is different than those same parts used in other uses like electronics. The guidance for aircraft use states to use a flat washer with the locking washer to protect the bearing surface from damage. Perhaps a call to JPI will answer the question why put the star washer between the terminals and not the nut?
Stewartb said:
Anyone else use Nord Locks? I like them.
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The problem with certain tension locking methods like Nord Locks is that they require special torque conversions as it changes the existing torque recommendations and guidance which is based on friction coefficients. The issue with accurate torque is why the current aviation tension locking method is to use safety wire. Even though AS may sell Nord Lock there are no torque conversion tables for their use during aircraft torquing applications. For example, the tension resistance by those washers will change the tension value on the bolt or stud being torqued. They tried tension devices like Nord Lock on the helicopter side due to the excessive vibrations and double-safety requirements of most hardware. But most never made it mainstream due to the varying hardware torque issues.
Robert Gee said:
So why use a star washer and not a split washer,
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The OEM calls out the specific washer requirement based on their needs. Star washers are very thin and are required to be discarded after each use. Split washers are much thicker and can be reused multiple times. So whatever the OEM decides it what you use.
 
Bell206 said:
FYI: you’ll find different applications (industries) use standard parts for different reasons. Existing guidance for the use of lock washers in securing aviation mount hardware is different than those same parts used in other uses like electronics. The guidance for aircraft use states to use a flat washer with the locking washer to protect the bearing surface from damage. Perhaps a call to JPI will answer the question why put the star washer between the terminals and not the nut?
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I think it's fairly obvious. The star washer "bites" into the relatively soft metal of the lugs it's sandwiched between, reducing the likelihood of a poor connection, and preventing the flat sides of the lugs from rotating.
 
Chip Sylverne said:
I think it's fairly obvious. The star washer "bites" into the relatively soft metal of the lugs it's sandwiched between, reducing the likelihood of a poor connection, and preventing the flat sides of the lugs from rotating.
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Thats one possible theory. But I've also heard spring washers are used in electrical connections to offset thermal differences between the steel attachment hardware and the aluminum electrical terminals. Regardless, it would be interesting to know JPI's reason considering aluminum and steel are dissimilar metals which can also lead to corrosion.
 
You put the star washer under the terminal lug because if you put it between the nut and the lug you are going to twist the lug off when you try to remove the nut. Ask me how I know...
 
I use them wherever I want on my Exp Cub and they work great. I torque them the same as normal. Nothing has loosened, and that’s a nice change.

One of the cool parts of forums like this is sharing new product pireps. One of the uncool things is some crotchety old dude shouting them down. You can have the floor.
 
Stewartb said:
I use them wherever I want on my Exp Cub and they work great. I torque them the same as normal. Nothing has loosened, and that’s a nice change.
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Ha! E/AB, thought so. But that’s not what you were implying. Plus you obviously don’t know how the Nord system works do you? In order for Nord Locks to work as advertised they need to torqued to a specific higher torque range. Calculating that torque requires selecting the material grade, friction coefficient, etc. which is completely different than the Standard Torque charts given in the aircraft manuals.

So if you don’t follow that higher torque value and “torque them as normal” you lose the benefits of the Nord locking system, i.e., your spending $1.00 for a special washer that provides no more locking ability than a new $.02 standard AN star washer does. FYI: the reason most hardware loosens is wrong torque used or they reuse star washers which are a one-time use item. Did you change your star washers each time prior to Nord use??

But since you won’t provide the torque example I will. Using the generic Nord torque table with a grade 8 material (which is close to MIL-SPEC materials) and their friction coefficients (lubed) Nord calls for 20 – 22 FOOT/lbs of torque on 5/16 x 18 thread. That’s 240 – 264 INCH/lbs. That same thread torque (dry) on an aviation standard torque table is 80 – 90 INCH/lbs… or 6.7 – 7.5 FOOT/lbs. Prior to your last post this is what you were recommending to the reading public… a 200+% increase in torque force. Is that one of the “cool parts” of posting you mentioned?

Stewartb said:
One of the cool parts of forums like this is sharing new product pireps. One of the uncool things is some crotchety old dude shouting them down. You can have the floor.
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Sharing new products is one thing. But setting up the next guy to utterly fail because you are clueless on how the product works is something completely different. It’s the reason I first posted on PoA and will call out this BS every time I see it. Floor’s yours kiddo….:rolleyes:










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On old cars star washers were used more for electrical paths as well as securing the bolt/nut. Old gennys and the ignition system required the entire metal structure to be grounded, and once painted that was hard to do.. so the star washer was used because it would dig into the metal. Once ignition/charging systems got better, the star washer fell out of favor unless specifically called for.

The wings on a star washer and the lip of a lock washer are there to provide tension against the threads to keep them in place. The digging into the metal is really a secondary feature. You can use a copper crush washer, an o-ring etc to provide that same tension if the environment allows it.
 
Can Nord Locks be used if the IPC calls out something else?
 
LesGawlik said:
Can Nord Locks be used if the IPC calls out something else?
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Yes, its considered a minor alteration. However, you need to use the required torques mentioned above and stay outside the applications not recommended by Nord as below, for them to work properly. If not, you're basically throwing your money away vs conventional locking methods costs.
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These split lock washers, wave lock washers, star washers, etc....basically they are the same as a flat washer. When compressed that's what they become. They do nothing for a properly designed, and properly torqued threaded fastener system. I'm not familiar with these Nord washers....but just based on first glance they might at least start doing something after a fastener loosens, unlike most of the other things, but by then it's sorta irrelevant...the joint has failed anyway.
 
Brad W said:
These split lock washers, wave lock washers, star washers, etc....basically they are the same as a flat washer. When compressed that's what they become. They do nothing for a properly designed, and properly torqued threaded fastener system. I'm not familiar with these Nord washers....but just based on first glance they might at least start doing something after a fastener loosens, unlike most of the other things, but by then it's sorta irrelevant...the joint has failed anyway.
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This is an incorrect statement, I’ll just leave it at that.
 
what force is required to flatten out one of those things? and what's the clamping for force for a torqued screw of that size?

In what sort of situation is it incorrect?
 
Brad W said:
what force is required to flatten out one of those things? and what's the clamping for force for a torqued screw of that size?

In what sort of situation is it incorrect?
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That’s what makes it wrong, they are never “flat”. They always exert tension on the fastener. You are correct in the fact that they will not replace a torque to spec fastener which is why they aren’t used on high stress fasteners.
 
Grum.Man said:
That’s what makes it wrong, they are never “flat”. They always exert tension on the fastener. You are correct in the fact that they will not replace a torque to spec fastener which is why they aren’t used on high stress fasteners.
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The star washers can be made flat and exert no tension. I've taken off many fenders with basically useless star washers. ditto for lock washers. They have a finate number of compressions before they become flat.
 
pfarber said:
The star washers can be made flat and exert no tension. I've taken off many fenders with basically useless star washers. ditto for lock washers. They have a finate number of compressions before they become flat.
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That is literally impossible due to a thing called spring back but ok I give.
 
pfarber said:
The star washers can be made flat and exert no tension. I've taken off many fenders with basically useless star washers. ditto for lock washers. They have a finate number of compressions before they become flat.
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Given star washers are a one time use item regardless of industry/application they should never get to that point. Any self-locking hardware has a finite life however some industries require you to check that ability or simply replace it every use. Then again I've seen people reuse cotter pins, safety wire, locking tabs, etc. either due to lack of knowledge or simply being cheap.
 
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