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

 

[CoryPad]

There are a range of adhesives, from low strength to high. They could provide the highest resistance or the least.

The distorted thread types will provide much higher resistance than the nylon insert or expanding type.

I recommend adhesives since they are strong and don't damage the mating part.

Are you having problems with the present curing time?

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[John2004]

Hi Cory,

Thanks for your reply.

Regarding your question, I have no real problems, I guess curing time could be reduced by heat as long as it doesn't get hot enough to hurt the Delrin washer under the nut.

I like loc-tite and adhesives as well, but it's just a matter of making sure the nut and bolt are clean, applying primer, applying the loc-tite, then waiting for it too dry.

I just thought if I could get a loc-nut to do the same thing it might be a better way to go from an assembly standpoint. From a strength and reliability standpoint, I really like loc-tite as long as it's applied correctly.

If I use a regular non hardened hex nut (maybe a grade 2 or a brass nut) could I tap a hole through the side (through one of the nut flats to the center of the nut) that would allow me to use a cone point set screw to lock the nut in place after it's snugged down, or would tapping the nut in this way mess up the nut threads so that it would not thread onto the bolt ?

If it could work, tapping the nut would be easy and set screws are cheap. Plus I would save time cleaning the bolts, applying primer, and waiting for the loc-tite to dry.

Once the cone point set screw digs in, I don't think it would go anywhere. It's just a matter of whether it can be done without messing up the nut threads.

Do you think it would it likely work ?

Thanks
John

P.S. Regarding those distorted thread type locking nuts, does it matter if they are top lock or center lock style ?

 

[CoryPad]

Distorted thread nuts aren't very different from each other. The top lock style enjoys more market share in the automotive market. I recommend one of these nuts to the set screw idea you proposed.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[MintJulep]

It largely sounds like you are trying to solve a problem that you don't have.

If the adhesive is working, why change?

Any type of self-locking nut is intended to supplement the resistance to loosening developed by properly preloading the joint.

The resistance to rotation provided by the self-locking mechanism is typically only a few lb-inches for a 1/4-28 fastener. The actual value is readily available in the manufacturer's literature, or the controlling standard.

For maintaining a nut on a bolt used as a trunnion - as in your case - a castellated nut and cotter pin is generally the preferred method.

 

[unclesyd]

To stay with the thread locking approach here are two avenues that might solve a few problems for you. This approach uses preapplied thread locker that takes care of the cleaning and application of the thread lock. One of the links is to a Loctite Product and the other two are to a NyLok product.
I've used both with very good results.

http://www.longlok.com/products_vibraseal.htm

http://www.nylok.com/products_precote85.htm

http://www.forestcitytech.com/products/thread_coatings/precote/precote.html

 

[Compositepro]

You could use a jam nut which is a second nut tightened against the first. Nuts made for this purpose are thinner than standard nuts but, if you have room, just use two standard nuts.

 

[unclesyd]

Here is a listing of all thread lock materials that are applied by Forest City. This cover nearly all materials available.

http://www.forestcitytech.com/products/thread_coatings/index.html

 

[John2004]

Per Mint Julep I found some castle nuts at Mcmaster for a 1/4-28 thread. If I cut the cotter pin off close I should have room for this method.

I will just drill a hole in the bolt at the proper position to receive a 1/6" OD cotter pin, and try to use the castle nut.

I'm not sure If I will be able to drill the grade 8 bolts I'm presently using so I may have to go to a softer bolt.

Thanks again guys,
John

 

[John2004]

Actually, even with the castle nut I will probably have to drill the hole in the bolt after the unit is assembled.

This is because I can't have any axial play in the bolt and if I pre drill the hole in the bolt, then I may have to back off the castle nut a little to get the cotter pin to align with the hole.

If a distorted thread lock nut is not reliable enough, it looks like I will probably have to stick with loc-tite, go to a different faster drying adhesive, or tack weld it.

Using a lock nut and loc-tite together may be an option since the lock nut would just have to hold the nut in place while the loc-tite dries, then once the loc-tite dries it's not going anywhere.

 

[IceStationZebra]

I have to add a disclaimer to CoryPad's assertion that distorted thread types have the highest resistance to removal. They normally do, but I have found that the quality control is not that good. 90% will be good, 15% will be too tight, and 5% will be too loose.

I would also steer away from the double nut idea since your main issue is taking all the slop out of the joint. You can do this with two nuts, but it can take three hands.

I would recommend a standard nylock nut. I have never had one come off even in sever vibration applications. (of course your results may vary ;-) ) And if you want a belt AND suspenders approach you could double-nut it with a standard nut.

ISZ

 

[MikeHalloran]

I'd use a nylok. But don't use Loctite with it; Loctite doesn't get along with every plastic.

<historical note>
Before unit bearings came along, the automakers developed some fine- resolution variations on the castle nut, in larger sizes. If you had serious volume, maybe you could tool up something like that, say with a straight knurled nut and a castellated sleeve with an internal knurl.
</>

There are also some variations on the Push-Nut that work on unthreaded rod, commonly used to hold wheels on garbage can axles. They work exactly once, just long enough to get through a short warranty. I hate 'em, but they're cheap, if that's an issue.







Mike Halloran
Pembroke Pines, FL, USA

 

[berkshire]

Surely the application here would be better off with a shoulder bolt, or would that cost too much money?
B.E.

 

[John2004]

Actually, with the castle nut even if I have to back the nut off to align the cotter pin with the hole in the bolt, If I can just snug the nut back down, that should bend the 1/6" OD cotter pin and then I don't suppose it will go anywhere.

It's just a matter of how far off the misalignment between the hole and cotter pin will be but I think the cotter pin should have some give with a good wrench on the nut and bolt. A belleville washer under the nut would be added assurance.

I used some small 10-24 top-lock distorted thread lock nuts before and years ago I used some of the nylon insert lock nuts to hold a small engine down that had been vibrating loose.

One thing I remember is that the distorted thread top-lock nuts seemed to have some inconsistency as icestationzebra mentioned. The nylon insert nuts seemed more consistent with respect to back-off torque and much more re-usable although I'm not really concerned with re-usability.

This is not directly related to my problem but just out of curiosity, I have seen the comments from NASA which I think Mint Julep posted on split spring lock washer's, do you think that belleville washer's are better than split spring lock washers, or do they also (as NASA stated about the split spring lock washers ) basically have no locking ability once they are flattened by the nut ?

Berkshire, a shoulder bolt would certainly be cheap enough, but I'm not quite sure what you are proposing. The nut must rotate with the bolt as one unit as the bolt is rotated to adjust a slider.

A bolt is inserted through a clearance hole in a flat aluminum plate. The bolt head is on the bottom side of the .503" thick aluminum plate, the nut is on the top side of the aluminum plate. There is a .036" thick Delrin washer between the bolt head and the aluminum plate and the nut and the aluminum plate. The nut is snugged down just enough to take up any axial play in the bolt. There is 1/2" of thread protruding from the nut that is threaded into a slider. Rotating the bolt moves the slider. The bolt head and nut only serve to keep the bolt from translating axially as the bolt is rotated.

I'm currently using a # 91257A565 bolt from

http://www.mcmaster.com.

Are you proposing that I use a shoulder bolt instead and just tighten the nut on the shoulder bolt until it bottoms out and then torque it down real good ? If that would work I would need to find a shoulder bolt with a 1/2" long shoulder and a 3/4" long threaded portion. I don't think that method would give me enough control to take up all of the axial play in the bolt and be consistent. That's one reason I did not use a C clip on the bolt, because I have to have zero axial play and the nut works good for that, plus the nut is strong and will never change due to axial loads.

The people doing the assembly are not crazy about the loc-tite method so I was trying to find a purely mechanical solution. Personally I like loc-tite as long as it's done right but I guess they feel the prep work and drying time are drawbacks.

I will just have to experiment until I find something I'm confident in. The nylon insert nuts would be great if they can be trusted. Otherwise, the castle nuts with a Belleville washer as a back-up may work.

Thanks again guys,
John

 

[hydtools]

Go with the ESNA nut. It will stay put. It gives you infinite adjustability for your application. Set it and the work is done. Loctite is not necessary; it would be the belt to go with the suspenders.
The castle nut gives you discrete adjustability which may not take all the axial play out of the joint. The installer has to decide when to install the pin. Could be loose, could be tight.
The bellville washer will not lock, it only provides a tension preload depending on how much it is compressed. This will axially load the joint which you want to freely move.
The split lock washer will not effectively lock until it is loaded tight. Then it will not allow the bolt to be rotated to move the slider.

Ted

 

[John2004]

Ted, by "ESNA" nuts do you mean the standard nylon insert locking nuts ?

http://www.aboveboardelectronics.com/approved/esna.html

http://www.spstech.com/aero/prod_lit/esna_catalog.pdf

John

 

[hydtools]

Yes. ESNA is the acronym for Elastic Stop Nut Corporation of America the original porducer of the lock nut. It has come to mean any brand of lock nut that uses an elastic locking element.

Ted

 

[carnage1]

is there a reason not to use a pair of jam nuts here? this is the perfect application for them. They are completely permanent, but can be adjusted later. For instance if the Delrin wears down a bit. as for three hands you don't need extra hands if your technique is correct. put on the first nut till it is exactly where you want it, put on the second nut till it touches the first. Hold the first nut with one wrench and tighten the second nut against the first.
you don't have to worry about backing off slightly to fit a castle nut, you don't have to switch to a lower grade bolt, you don't have to wait for drying time and if after some wear it needs readjusted it could be readjusted without a reduction in holding force.

 

[John2004]

I could give the jam nuts a try, I would just need two that are together, about the same thickness as one standard nut.

If the nylon insert lock nuts work though, that would be the way to go.

I've never used two jam nuts for something like this and I was not sure if the technique would be reliable enough. I guess I kind of felt they might loosen up over time and I can't have that.

I used a jam nut technique a while back when I had to remove some threaded studs from an old water pump. The studs on the old pump had to be transferred to the new pump. These are the studs that hold the fan onto the pump and they have no head or anything to get a wrench on ( 4.3 V6 pickup engine).

I screwed two standard nuts on the stud, tightened them against each other, and then used the bottom nut to back the stud out.

 

[berkshire]

John2004
Yes I was proposing getting a shoulder bolt the correct length and just screwing the nut down to the shoulder.
that was before I realised that you were making fine adjustments with the nuts.
To do what you want two AN316-4 half nuts should work just fine.
B.E.