Flat washer direction

[floattuber]

Maybe I missed this in the search, but I didn't see this topic posted before...

Recently, one of the grey beards (or mustache in this case) said to always put a washer on a bolt a certain way. The washers are stamped so often times there is a curve or bow to them and they also have a slight edge where the stamping tool cut through.

I've never heard of this. Is it true that there is directionality to washers?

 

[IRstuff]

I doubt it. There was a thread on lockwashers being ineffective, and if that's case, any tiny bow is equally irrelevant.

TTFN

FAQ731-376

 

[KENAT]

Depends.

If the washer is there to prevent the surface of the part being damaged while the bolt is torqued, then it makes sense you wouldn't want any burrs or similar sharp edges or similar defects in the washer facing the surface to be protected.

That said many washers don't exhibit such a noticeable curve/bow/burr etc. in which case it would be difficult to say which side should go up/down.

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[MintJulep]

We have visited this before.

thread404-147252

The specs that define washers do not make any mention of "sidedness".

 

[rb1957]

sure cheap washers, stamped out of sheet, have a smooth radiused side to the bore and a sharp side (where the punch has sheared through the sheet). there's a story i've heard (but it could be an urban legend) that there was a plane crash caused by a washer being placed the "wrong" way (so that the sharp edge initiated a fatigue crack).

looking at MS washers in our parts store, they don't show this feature.

 

[floattuber]

I've read that lock washer thread before but missed the one Mint linked.

Our MS washers also don't have this problem.

I didn't think it would matter considering the hundreds, thousands or tens of thousands of pounds of force that a bolt can produce. The only thing I could think of was that the burr might prevent full engagement of the washer and over time and vibration, it would wear away and reduce the preload.

 

[Twoballcane]

He may be talking about fender washers? The do have a bow to them.

Tobalcane
"If you avoid failure, you also avoid success."

 

[SnTMan]

I normally put cheap stamped washers for unimportant applications with the burr side down just for the appearance. If it was an important application I don't believe I'd use a cheap stamped washer

Regards,

Mike

 

[floattuber]

No, we were using cheap COTS washers for a somewhat large piece of equipment, not fender washers. This was not an important application.

 

[MikeHalloran]

I usually put them burr side up so they won't damage the paint. ... but I'm not aware of a rule. MS washers are not supposed to have a burr, of course.



Mike Halloran
Pembroke Pines, FL, USA

 

[Ron]

Yes, they are directional, based on the stamping. It makes no fundamental difference how they are installed....as you see by the posts, there are opinions either way; however, for the reasonable term of their life, these are not significant.

 

[Artisi]

Just make sure you don't install them

 

[Tmoose]

If a joint relies on maintaining preload I'd make some effort to keep paint out of all the clamping surfaces.

Some users of TruArc type snap rings consider them "directional" based on the relatively rounded and square edges from manufacturing.

The TruArc literature is more concerned about chamfers or radiuses on abutting part that tend to bend or twist the ring by applying loads offset by the chamfer distance

 

[juergenwt]

Washers (high quality) are made in compound washer dies and are flat on both sides with very little roll over at the edges. That is because the compound (washer) die hits home and the shedder acts as a flattening agent.
However cheap washers punched out in a progressive die can have quite a roll over at the edge because depending on the material thickness you have to leave a clearance between the punch and the die - usually 6% total on perforations. If you use the washer with the roll over side down against the surface, you will loose some of the contact surface which can be quite significant.
Quite often one die is built to accommodate a wide range of material thickness and so the die is made with a clearance for the thickest material to be punched resulting in a large roll over for thinner materials. Some (cheap) washers look absolutely terrible.
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