Do you see anything wrong in these pictures? The supplier hadn't noticed any issues :-) 1

[Chris C]

Previously sent this to a bunch of folks in my personal e-mail lists with varied results/feedback.
Curious to see what the Eng-tips audience says of these:

 

[Compositepro]

I suppose you mean that the twist of the teeth is "wrong" for retaining a right-handed screw or nut. I'm not sure it really makes a difference in real life. Many say they do not work, period.

 

[Chris C]

First response winner! Yes, I've heard that their value/utility is questioned. Would be interesting to see a study on it.
Regardless, I suspect there is a specification for these type of washers that isn't met; probably a mil-spec as a guess.
If anyone knows of specs particular to these type of washers, I'd appreciate the references.

 

[Compositepro]

They could be made specially for left-handed screws.

 

[TugboatEng]

Please don't be using those in a marine environment! They let water under the head of the fastener and cause them to seize.

 

[3DDave]

MS35333, now per NASM35333.

On

https://www.wclco.com/lock-washers/...rnal-type-lock-washers-standard-and-mil-spec/

I found they list left-hand twist in some sizes, so maybe confirm with supplier.

 

[hydtools]

Nord Lock may have done a comparison test.

Ted

 

[TugboatEng]

Nord-Lock might be the best iteration but I despise lock washers. FYI, Heico has a comperable product line for much less mulah for our Oosa residents.

 

[3DDave]

Off-topic, but why hasn't there been a helical split, toothed lock washer with internal and external alternate twist teeth?

Best of the best and should be a winner.

 

[TugboatEng]

Because all forms are bunk?

https://ntrs.nasa.gov/api/citations/19900009424/downloads/19900009424.pdf

 

[JohnRBaker]

Yes, and when I worked designing machinery for bakeries, these were not allowed as they provided a place were 'vermin' could live.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[TugboatEng]

The only lock washers I have researched and purchased were 10mm Heico wedge-lock units in Inconel 750X because I didn't want to lay the $50 per washer price ABB turbocharger wants for their 1 time use folding type washers and there were 12 per turbo that had to be folded and tossed at every install/removal (think of the labor). 200 of the improved washers were the same price as 12 of the one time use units. Sadly, we retired that turbocharger series after only using 12 and my boss thinks I wasted our money? Now he wants me to store that $600 box of washers that I have no use for and that has already paid for itself. Anybody need 188 Inconel 750X lock washers? *end rant*

 

[3DDave]

I left off the /s. Not working well has never stopped certain things from selling well. Just surprised no one tried it.

 

[Tmoose]

Using any kind of a lockwasher that uses "digging in" to the fastener and/or the clamped part intending to prevent loosening-by-turning is way too hypothetical for me.

Even if the fastener does not rotate at all, I fear the increased potential for a few 0.001s" embedment over time, and subsequent loss of clamping is practically the same as the cherished and carefully nurtured fastener elongation at installation.

 

[btrueblood]

I thought the only purpose for the toothed washers was to dig through paint and other coatings to create electrical contact (I only ever see them on grounding screws in electrical cabinets, but then I lead a somewhat sheltered life).

 

[drawoh]

First response winner! Yes, I've heard that their value/utility is questioned. Would be interesting to see a study on it.
Regardless, I suspect there is a specification for these type of washers that isn't met; probably a mil-spec as a guess.

I have on my bookshelf Handbook of Bolts and Bolted Joints, by John H. Bickford and Sayed Nasser. It contains an extensive discussion on bolts coming loose, and lock washers. It concludes that lock washers generally are useless. The Nord[‑]Lock washers, noted above, are highly recommended. As also noted, Heico and Disc[‑]Lock washers are equivalent.

Also, check out Bolt Science's website. There is lots of stuff there too.

--
JHG

 

[Tmoose]

From the NordLock site.

https://www.nord-lock.com/nord-lock/technology/

How it works ( The section Nord-Lock X multifunctional wedge-locking technology, not standard NordLocks)

Upon tightening the fastener, the X-series washer flatten and the serrations engage the contact surfaces
Since the cam angle α, is larger than the thread pitch β, the wedge-locking effect prevents any rotation of the fastener
Directly after tightening, the joint settles and the fastener sinks into the surface material
The washers immediately deflect and the spring effect (Fs) counteracts the slackening movement of the bolt, preventing loss of preload on the joint​

I believe that is an acknowledgement that standard Nordlocks serrations embed into their faying surfaces as expected, but do nothing to compensate.

Years Ago I looked into into belleville washers a few times to simulate a longer "grip length" with the well proven benefit of retaining fastener preload after bolts and bolted surface embed a little bit.
My conclusion was, for Grade 5 and especially Grade 8 fasteners, and SHCSs, to maintain preload/clamping similar to the original installation, the stack of commercial bellevilles necessary was Quite tall.

A 3/8" Nordlock X pair/set is 2.6 mm thick. Say 1.3mm .06" thick each.
A single Belleville steel washer for a 3/8" bolt has a calculated at flat load of 760 lbs or less.

https://www.leespring.com/belleville-washers

If a 3/8"- 16 SHCS is torqued to 75% of proof load the resulting clamp load is about 8000 lbs.
So a .6" inch tall stack of at least 10 commercial bellevilles in series will be needed to provide a meaningful clamp load should the fastener just start to loosen, or embed in service.
The stack will compress about 0.07" going from barely snug to torqued flat.

 

[FACS]

The only thing those should be used for is electrical grounding lugs.

 

[TugboatEng]

When you buy these types of washers from the manufacturer they will ask about the hardness of the two surface. The serrations need to imbed deep enough so that the load is carried on the flat faces of the washer.