Recommendation for self locking nut with greatest removal resistance

[John2004]

Hi everyone,

I'm hoping someone having experience with self locking nuts can help with the following.

I need a self locking nut to be used on a 1/4-28 thread bolt. I'm not going to really torque the nut down, I'm just going to snug the nut down to take up any linear or axial play in the bolt.

The nut will actually "rotate with" the bolt as the bolt is rotated in order to adjust the position of a slider. There is a Delrin washer under the nut. The only thing that can really cause the nut to back-off would be if the friction between the nut and the Delrin washer during rotation, is greater than the torque required to loosen the lock nut.

Presently I'm using loc-tite and it works OK but I would like to see if I could just use a stock lock nut. The nut will never be reused or anything, basically just snugged down, set and forget. There are also no vibrations present.

I've listed the choices of lock nuts that I have from mcmaster carr below.

90566A210 (Nylon insert type Lock nut)
94830A515 (Expanding type lock nut)
91837A250 (Distorted thread type lock nut, top-lock style)
90040A120 (Distorted thread type lock nut, center-lock style)

Can anyone tell me which nut would provide the greatest resistance to removal with a standard wrench ?

Even if I have to keep using loc-tite, I might still use the lock nut since the locking feature of the nut could hold the nut in place while the loc-tite dries.

Loc-tite is good stuff but it just seemed that a self locking nut may be better from an assembly standpoint, and I won't have to wait for the loc-tite to dry.

Any feedback would be appreciated.

Thanks
John

 

[evelrod]

From the 'practical application' side of this...
I use four NAS 1/4-28 bolts to attach the mounting bracket assembly for my oil cooler. The mount is 'flexible' in that it has a white Delrin compression sleeve with Delrin washers under steel AN washers on each end of the bolt. I use a simple Nyloc nut on each 'snugged up' to allow some movement since this is a race car application with moderate to severe vibration potential. No failures in seven seasons.
Maintenance is frequent and although I re use the bolts, I always put on new nuts...That's cheap insurance.

Rod

 

[John2004]

Thanks for relating your application experience evelrod.

I will probably give the nyloc nuts a try first.

Just out of curiosity, regarding the jam nut technique, would I be better off to use a right hand threaded nut and a left hand threaded nut together ?

If only one right hand threaded nut were used, then rotating the bolt in one direction would tend to tighten the nut and rotating the bolt in the other direction would tend to loosen the nut. If I put a left hand threaded nut on top of the right hand threaded nut and tighten them against each other, when the bottom right hand threaded nut tries to back off and loosen, it would immediately cause the top left hand threaded nut to tighten down.

Unless I'm missing something it seems using one left and thread and one right hand thread jam nut would almost be fool proof ?

John

 

[KENAT]

I haven't fully read all responses but based on what sounds like similar situations, I've found the nyloc worked well. No type of 'sring' washer, be it wavy, split... seems to work that well so I'd be sceptical on that one.

I've had trouble with jam nuts in a similar situation but it maybe be because I wasn't using them correctly. There have been posts on hear before about jam nuts & how they work etc, worth looking for if you think it's a way to go.

KENAT, probably the least qualified checker you'll ever meet...

 

[handleman]

The left hand/right hand thing depends on which is harder - the nut or the shaft. If the shaft is harder, there won't be any threads left in the left-hand thread nut by the time it gets down to the other nut. If the nut is harder, it may act as a die to recut left-hand threads in the bolt, thereby preventing the right-hand threaded nut from backing off.

-handleman, CSWP (The new, easy test)

 

[Timelord]

Huh???

Unless I am misinterpreting something, I would like to see how you get a left hand and a right hand nut on a single threaded shaft. Right and left hand threads do not mix!!

Timelord

 

[KENAT]

Good point Timelord, both nuts have the same handedness, which tends to match the handedness of the shaft.

thread311-164764
thread725-188550
thread725-57042


KENAT, probably the least qualified checker you'll ever meet...

 

[MintJulep]

Putting a left-hand nut on a right-hand bolt pretty much guarantees that it won't come off by itself.

It is difficult to control the point at which the pair will lock up however.

 

[John2004]

Yes, Good point timelord, that's what I get for overthinking nuts & bolts

One last thing occurred to me, it would be kind of overkill for me but may work well if someone else has a similar situation.

The Delrin washers could be replaced with needle or ball thrust bearings with steel thrust washers. This would allow the nut to be torqued down pretty good, and the bolt would still rotate easy. Even a regular non-locking nut would probably stay on pretty good with this method and the bolt could support high axial loads as the delrin washer is presently the weak point. Also, any problem with wear on the Delrin washers causing axial play would be eliminated.

In any event I suspect the nyloc nuts will be the best alternative to loc-tite.

Thanks and take care guys,
John