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washer selection
2

washer selection

washer selection

(OP)
I'm wondering when should lock washers be used?  Do they always have to be used with a flat washer?  Does it matter what order they go in?

As well, in the past I had been using washers on the bolthead side of a connection.  On this current project they are stating to always put them on the nut side of the connection.  Does it matter?

I have no idea about any of the factors to determine when to use what and when.  Any help would be appreciated.

RE: washer selection

49078:  

If you are using lock washers they should go above the flat washer and below the bolt head (or nut)  Usually the wrenching surface (bolt head or nut) with the washer is held and the nut ot bolt head is tightened.  The flat washer always goes against the surface to prevent damage by the lock washer.

Regards
Dave

RE: washer selection

The flat washer also spreads the clamping load.

rmw

RE: washer selection

(OP)
Should I ever need to use two flat washers? One on both sides for anything other than fixing possible spacing problems?

RE: washer selection

I have never had much luck with the spring loaded lock washer.

If the torque of the nut and bolt doesn't hold the fastener together, then how can the spring of the washer (which must be less than the torque of the bolt) do anything?

In my experience the nylock nut works better. I would be interested in hearing what anyone else thinks.

RE: washer selection

49078,

You only put a flat washer under the turning element, either the nut or the bolt head, depending on how it is being tightened.  For some interesting discussions on split lockwashers try the following threads.  There's some good advice there.

thread725-145968
thread108-114051

Regards,
-Mike

RE: washer selection

I was wondering what the consensus is on whether or not washers that have a rounded and a flat side should always be put on the flat side down to the mating surface?
I'm trying to convince some co-workers that the above is a good idea and therefore increase consistency and reliability in our assemblies.
Some say that there is no difference and that its just a piece of metal.  I feel that there is more surface area in contact with the mating surface with the flat side down and therefore a stronger connection.
Thank you!

RE: washer selection

2
Don't use split lock washers, they don't do anything.

Flat washers should be used under both the head of the bolt and under the nut.

RE: washer selection

Spring Lockwashers become flat and have NO grip when the hardware is properly torqued.  I agree with people who say they are somewhat worthless in keeping a nut or screw from "coming loose".  My opinion is that they may (may) help the nut from falling off after it becomes loose, but I don't like them all-in-all.  Proper torque is your answer for assemblies to stay together.

Flat washers always, and on both sides, if bolting thru "slots" as opposed to holes.

Many other types of lockwashers (other than one-split spring-type) are available and do work on small screws.  People who have said "place the lockwasher next to the nut or bolt-head" have my agreement (if you must use them due to Assemblers not willing to do it differently, or bosses who require them).

RE: washer selection

Oh yeah...to respond to intentsly: The cross sectional shape of the flat washer is more likely a result of the way it's manufactured not design-intent.  I don't believe it makes any difference which side is up.  Think about using a fender washer if you want to cover more surface under the screw-head. :)

RE: washer selection

intentsly: Flatwasher really doesn't matter which side is down (except maybe appearance).  If you want more contact-area use a larger washer.  I don't think the shape of the washer is a design-intent, but a result of fabricating the washer itself.

RE: washer selection

intentsly,
The rounded side goes toward the bolt
head to help assure clearance at the
elliptical radii on the bolt under
the head.  So you are right in that
the flat side is designed to go
on the structure side.  Some washers
have a chamfer instead of a radius
on the id of the washer for the same
purpose and only on one side.

RE: washer selection

ASME B18.22.1 "Plain Washers" does not discuss flatness or a radius or chamfer on the ID.  The dimensional tables and associated illustrations do not show a radius or chamfer.

ASTM F844 "Unhardened Steel Washers" allows (not requires) washers to be out of flat within limits, and perscribes a method of measurement.  It refers back to B18.22.1 for dimensions.

ASTM F436 "Hardened Steel Washers" allows (not requires) washers to be out of flat within limits, but does not perscribes a method of measurement.  There is no radius or chamfer indicated in the dimensional tables and figures.

From this I conclude that washers manufactured to any of these standards are not intended to be "sided".

RE: washer selection

Thank you for your replies.  I do understand that the washers we use are manufactured by stamping causing a rounded side and we have no choice in the type we use, as we are building to a customer's drawing specification (gov't work ;) ).  I think that the round shape would work better on the bolt side mating surface as our bolts tend to have a radius where the washer's id would mate.  I'll put your replies into the ears of my coworkers.  Thank you!

Larry

RE: washer selection

I would love to overhear the conversation between the assembly technicians and the engineer where the engineer explains that the orientation of every freakin flat washer needs to be ascertained so that the washers can be installed in the correct orientation.

I would also love to be there when the government inspector comes in, reads the process instruction explaining washer orientation, and starts checking for correct orientation and starts rejecting stuff for incorrect washer orientation.

Do you people ever get out on the shop floor?

RE: washer selection

I do assembly on the floor and find that work ethics are always at different levels.  This seems to correspond to certain age groups as well.  Being ex-Navy myself, I seem to feel a bit more responsible for the quality of the assemblies that are being made, since they are deployed on military crafts.  So, its not so much a question of it being a requirement, but a feeling of doing the right thing.  If all washers are put on in the same orientation at all times, then how could the assembly not be consistent time after time?  A sense of team spirit/comaraderie goes a long way as well, and if it can enhance the quality of the assemblies I will keep pushing in that direction. :)  Thank you!

Larry

RE: washer selection

Is the clearance so tight that this is necessary?  Or is this another $300.00 hammer situation?

RE: washer selection

In my case, its not a requirement to put a washer on one side or the other specifically.  I'm just trying to get ammo for my opinion and see if I can get the reluctant/non-caring to consider doing the assemblies all the same way. Cohesion is the goal, not just the occasional adhesion.  Thank you.

Larry

RE: washer selection

The clearance between the bolt shank and the washer i.d. allows room for the fillet under the bolt head.  Even if that were not true, bolt heads are hard relative to flat washers, and can easily form the washer to a shape complementary to their own fillet.  Hardened washers are an obvious exception, and are nearly always chamfered on the i.d. for obvious reasons.

In my own personal work, where assembly time is not an issue, I prefer to put the radiused face of the washer under the bolt head, not because of anything to do with the bolt, but because the o.d. of the washer is usually radiused on the same face, and a washer installed with the radiused face out is less likely to slice flesh that comes into accidental contact with it.

Similarly fussy individuals might wish to install washers the exact opposite way, so as to not cut through whatever paint film or wood lies under the washer.

Really fussy individuals just buy better washers with less of a die break burr.

Mike Halloran
Pembroke Pines, FL, USA

RE: washer selection

I agree also that the radiused side would prevent damaging other things that might come in contact with it, such as cabling/wire insulation etc..  This, in my case, is not so relevent due to the way they are made, but a good thought none the less!  Nothing wrong with adding value to a product by making it safer for use ;)

Larry

RE: washer selection

There is an industry standard for a better quality flat washer.  If you callout a "Finished Washer" in a particular size you can get much better quality product.  There is a slight premium on small lots, but this differential diminishes quickly with quantities.    

RE: washer selection

Intense,
It will not matter one iota in how your assemblies perform how the flat washers are oriented.  The differences caused by your use of "lockwashers" will far outweigh any influence from the orientation of the flat washers.
If you are using unhardened washers your loads must be relativley low so you won't see significant embement.
  
You need to worry about the level of hydrogen relief in those lockwashers if you want to assure good product for the troops.  They are notorious for stress corrosion cracking.  That is one of many reasons why I won't use them.  Make absolutley sure that those lock washers have been baked way more than the minimum spec if you don't want to have broken washers all over the deck when they see salt water.

Dick

RE: washer selection

I hope that "49078" is still reading this thread.  There has been much more discussion on washers than was originally asked.
If we are now talking about "value added" and "quality", neither is a result of orienting a flat washer a certain way.  If the Assembler must inspect and be aware, (and in worst case disassemble and reassemble) because someone wants a washer-radius out instead of in this does NOT add value to the mechanism/assembly.  Functionally it is the same...appearance is negligible.  Why beat this anymore?  Just call for the components on the BOM and your job is done.  If you want to use just a flat washer...call for it, if you want lock washer first then flat...say so, IF YOU WANT FOUR WASHERS STACKED UNDER THE NUT...OK!  There are situations for any scenario.  But, do you specify a torque on your assembly drawing?  That's at least as important.
I like the nylon-lock nuts (ESNA) and flat washers.  My opinion. :)  Less problem with vibration-caused loosening, and they are readily available in plated or stainless.

RE: washer selection

We don't have a say as to what goes on the BOM.  I wish it were as simple as getting the parts we wanted or assembling something a different way.  We build to print and don't have much say unless something is obviously causing a problem.  
I think, if something is assembled the same way each time, that it does add value.  Repeatability and attention to detail that goes into complex assemblies adds tons of value in not having to do rework.
Our assemblies are thermal tested and vibration tested as well.  The thermals are brutal and vibe is no lightweight either.  We also use larger washers where appearance tends to make all want them to go the same way.  Why not just do it for all of them?  End of Rant :)

RE: washer selection

Quote:

"I think, if something is assembled the same way each time, that it does add value.  Repeatability and attention to detail that goes into complex assemblies adds tons of value in not having to do rework."

I agree with you, its just a good idea. It may have no engineering basis but makes sense.

Nick
I love materials science!

RE: washer selection

(OP)
Well I never thought this would be such a popular thread.  It was interesting to keep up with it.

RE: washer selection

Thank you, for putting up with my additional question of washer orientation! :)

Larry


RE: washer selection

Larry- is that povray?

RE: washer selection

NickE-
It is a three axis HDR (High Data Rate) Submarine Satcom Antenna.

Larry

RE: washer selection

IRStuff-
FYI MS16212 is inactive for new design.  I use MS15795, NAS620, and AN960.  These seem to offer everything I've ever needed except a reduced diameter washer for No. 1 screws.

Tunalover

RE: washer selection

larry- povray is a raytrace/rendering software, I thought the image might have been created using it. Thanks

Nick
I love materials science!

RE: washer selection

NickE-
I thought thats what it was, lol, but just wasn't sure exactly what you meant.  Its just a standard realtime pic in jpeg format.  I think the cad/rendering software our company uses is solidworks.

Larry

RE: washer selection

Tunalover, you might want to review SAE J2655.  We on the SAE Ships Systems Technical Committee-Fasteners Subcommittee wrote it to replace the numerous Mil and Fed specs for washers. The Mil and Fed Specs are out of date. For example no one really manufactures to the dimensions for flat washers specified in Mil Standards unless they're ASME.  J2655 gives us an up to date industry standard and will promote standardization and reduce costs.  It's now been invoked for the new generation aircraft carrier being designed. I'm presently working on some minor updates for a new revision which we hope to publish by the end of the year.  

RE: washer selection

CVN78-
Unless J2655 issues part numbers that are recognized by fastener distributors I'm afraid we can't buy to it.  Even if the spec issues part numbers our buyers (not being very resourceful) would refuse to make multiple phone calls to find a source.  What about that new ASME spec that has a part numbering system for most common US standard fasteners?  I can't recall the number.

Tunalover

RE: washer selection

Tunalover-
 The great thing about J2655 is it's simplified PIN system. Five fields at most to fill out.  ASME system horrible, it's too long and complicated.  If you wanted Series 300 Cres (without the free-machining garbage) with J2655 you can put in one designator whereas with ASME you can only list one alloy which would you force you to list multiple PINs.  RevCar Fasteners in Roanoke Va. who is our primary supplier is versed in J2655.  They sell to the Navy and industry.  

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