Since the nut compression relies on deformation of the threads, these are single use nuts, right?
rogerdodger:
--- Quote from: bb2fish on July 11, 2019, 04:05:42 PM ---well isn't that snazzy.
Since the nut compression relies on deformation of the threads, these are single use nuts, right?
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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
[WR]:
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.
rogerdodger:
--- Quote from: [WR] on July 11, 2019, 07:10:12 PM ---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.
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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
rogerdodger:
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.