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Topic: All metal SS lock nuts  (Read 4145 times)

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rogerdodger

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bb2fish

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How is this nut a "lock nut" ?     Looks like a plain old nut made out of stainless steel. 

In the PDF document, The geometry of one side of the nut is tapered differently on the outer diameter of the nut (where the wrench flats are) - but I don't get it...what makes this "lock"?  Are the threads tapered on the inner diameter where the bolt engages??  Or is there some softer material (but still stainless) on the insert?


Shin09

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I think its the second nut (half size nut) for a 2 nut, lock nut setup.  But I could be wrong. 


Mojo Jojo

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There compressed on one side of the threads so as you crank them on they get harder to turn. Axle spring bolts are like this and are pressed hard enough it leaves marks on the presses side. Think about heating and flattening a pvc tube fitting then ram the occasional in, it stays there if you can get it to penetrate into the flatter end. 

Edit: you can actually see the compression dimples on the nut in the above photo...... no not my avatar !
« Last Edit: July 11, 2019, 11:27:14 AM by Mojo Jojo »



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rogerdodger

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There compressed on one side of the threads so as you crank them on they get harder to turn. Axle spring bolts are like this and are pressed hard enough it leaves marks on the presses side. Think about heating and flattening a pvc tube fitting then ram the occasional in, it stays there if you can get it to penetrate into the flatter end. 

Edit: you can actually see the compression dimples on the nut in the above photo...... no not my avatar !

exactly, "Uniquely shaped threads provide a vibration resistant friction fit, so the nut stays put. These all metal locknuts withstand higher temperatures than nylon insert locknuts. Top thread section is deformed to create two or three locking zones; they start easily by hand, then must be wrenched into final position."

I knew these existed for high vibration/temperature applications (the big block in my 68 Camaro used them to hold/adjust the valve rocker arms), but I didn't know they were available in SS until someone on Youtube tipped me off... ;D 
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bb2fish

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well isn't that snazzy.

Since the nut compression relies on deformation of the threads, these are single use nuts, right? 


rogerdodger

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well isn't that snazzy.

Since the nut compression relies on deformation of the threads, these are single use nuts, right?

I don't think so, the nyloc are definitely single use because the nylon cuts and deforms but these all-metal nuts with slightly deformed threads at 2 locations on the top, as they are tightened onto normal threads, those bent threads first deflect elastically, followed perhaps by a small amount of plastic deformation the first time.  But the elastic strain will always be there, providing a level of 'clamping' on the threads. 

It's the same principle in play when you try to straighten a bent piece of metal, you need to over-bend it so that when it 'springs back' (due to the elastic stress), it ends up straight.   A big help here is the high elastic modulus of steel, if you tried this with low elastic modulus materials (like nylon or aluminum), you don't get much locking behavior.   

I just finished putting a set on my drive and something interesting is happening, I have a feeling someone might be able to guess what it is.  (hint:  it would not be happening if the nuts were deformed at 3 locations 120 degrees apart)... cheers, roger
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[WR]

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Barb, Yes Single use only. We use these in a lot of different applications where I work. Torque specs and  engineering instructions tell us remove and discard , do not reuse. Depending on metallurgy, they can be soft or extremely hard, which can translate into broken and deformed hardware if you don't pay attention. 
Why so many odd typos ? You try typing on 6 mm virtual keys with 26 mm thumbs....


rogerdodger

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Barb, Yes Single use only. We use these in a lot of different applications where I work. Torque specs and  engineering instructions tell us remove and discard , do not reuse. Depending on metallurgy, they can be soft or extremely hard, which can translate into broken and deformed hardware if you don't pay attention.

I am curious, are you using SS or hardened steel (graded) top-lock nuts?  I am guessing they are hardened steel nuts. 

the reason I ask is that 18-8 (304) is a low carbon austenitic SS (stays face centered cubic at all temperatures), which means it cannot be strengthened through heat treatment (makes it easy to weld) and even work hardening has a limited ability to increase it's strength.  Typical yield strength for 304 is only about 30ksi and is very consistent, however it has excellent ductility which allows it to be deep drawn into things like sinks.  these nuts are corrosion resistant, not high strength.

the are other classes of SS that can be hardened, but 18-8 isn't in one of those. 

another factor here is that in this application, these nuts are not being torqued in place, they are primarily taking up slack in the drive cables,  and then (hopefully) staying put.

whether these nuts are going to work well on drive cables with flats on 2 sides is yet to be determined... ;D 

cheers, roger   

http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MQ304A



« Last Edit: July 12, 2019, 07:33:08 AM by rogerdodger »
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rogerdodger

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Ready to test the drive tomorrow.  Safety glasses on!

installing the top lock nuts went smooth, they did not require excessive torque, not enough to damage the plastic slot, but they did require a wrench.  Because the deformed threads on the nuts are 180 degrees apart, they align with the flats on the cable ends, which means the nut is not really locked in place when the deformed threads are over the flats.  However, they are trapped in that position by the threaded parts of the cable end, to turn them past those threads takes a wrench.  It's sort of like a crenelated castle nut that is secured with a cotter pin, they can be wiggled back and forth a bit but not turned further.

top lock nuts installed, cables correctly adjusted and deformed nut threads on side 1 are positioned over flats, on side 2, the deformed nut threads are over cable end threads:



to protect my drive during my test outing, just in case these nuts are able to loosen, I used some Blue loctite to hold normal SS nuts in place (taking care to get no excess loctite on the threads between the nuts).  I used a 1.5mm allen head wrench as a feeler gauge to set those normal nuts 1.5mm back from the top lock nuts.  1.5mm is just slightly more than 1 rotation of a 20 thread/inch nut, this will make it easy to determine if any of the nuts have loosened.



My expectation is that the nuts on side 1 will try to loosen just to the point where the deformed threads 'catch' on the cable end threads.  The nuts on side 2 with deformed threads positioned over cable end threads will hopefully stay in that location.  Regardless, if any of them are able to loosen enough to make contact with the normal nuts, that will stop them there before any cables get loose enough to damage my drive.

cheers, roger

 

 
« Last Edit: July 12, 2019, 01:01:29 PM by rogerdodger »
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[WR]

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Roger, check your mail.
Why so many odd typos ? You try typing on 6 mm virtual keys with 26 mm thumbs....


rogerdodger

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OK, I have a result, a negative one.

Some of the top lock nuts, one on each side, were not getting enough of a grab on the threads and were loosening up when I checked after 30 minutes on Munsel Lake.  I'm not sure if this is due to manufacturing variation in the nuts or differences in the cable ends, which only have short segments of threads on two sides due to the flats on each side.

Conclusion:  SS top lock nuts not going on my drive.

I have decided to go with my previous solution:  I installed brand new SS nyloc nuts, tightened to correctly 'tension' the drive cables, and backed them up with a normal SS nut that is tightened up against the nyloc nut and has some blue loctite applied to its threads.



Safety Glasses Off!  Fish On!   cheers, roger

 
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bb2fish

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Even though you had negative results, this information is very informative and useful.  Thanks Roger!


INSAYN

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Roger, I'm curious what your pedal strokes are like. Are you all shaky and vibrate while you pedal along?  You seem to have an issue with them backing off pretty frequently.

I've been rocking my 2010 Revo since new, and never had a drive nut loosen on me that I can remember.
I carry spare Nylocs in my first aid kit but never needed one yet. 
 

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rogerdodger

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Roger, I'm curious what your pedal strokes are like. Are you all shaky and vibrate while you pedal along?  You seem to have an issue with them backing off pretty frequently.

I've been rocking my 2010 Revo since new, and never had a drive nut loosen on me that I can remember.
I carry spare Nylocs in my first aid kit but never needed one yet.

no, I would say my pedal strokes are smooth, I'm not a high effort/work the drive hard guy, more of a 6 to 7 hour steady effort guy.  I put more than 100 outings on the V2 drive that came with my 2012 PA12, then no issues with lots of outings on the GT drive from my i11s, I am now over 20 outings on the 180 that came with the new Outback.  And I have never had any issues with nuts loosening on any of my drives until the outing on CoosBay on May 29, when just 1 of the nuts almost fell off, the other 5 had not moved.  I had definitely given several of the nuts a bit of a tighten before that outing, but I occasionally tightened the nuts on my earlier drives as need, never had one loosen up.

I have also never needed to take apart any of my drives (upgraded one from ST to Turbo fins, replaced one bent mast, and put the solid crank arms on my V2, that's it), so I have never replaced any of the nuts, just a slight tightening now and then to keep the cable tension correct.

my guess now is that one of the cable ends on my new 180 drive had a sharp edge that, when I tightened it like half a turn before the May 29 outing, cut the nyloc material enough that it just lost all it's locking ability.

cheers, roger   
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