Request for recommendation for self locking nuts with highest resistance to removal

John

Even simpler. Get two jam nuts from your friendly hardware store and jam them together. Maybe a washer between them if you like.

Bob AZ

in aviation we use the first and third types. I find that the third type has a stronger hold than a nylock.

look up 'Nord-Lock' on google. this is a little double washer that sits under the nut. it has stepped faces that make the release force of the nut higher than the forced used to snug down the nut. it may be a way of achieveing what you want. you could use plain nuts or nylocks with them.

Stealth Pilot

Stealth Pilot missed the REAL thing we use in aviation when we don't want the nut to come off, it's called "saftey wire"

It's also pretty tough to get a castle nut to move when it's got a cotter key through it.

If you are serious about NEVER removing this nut try some "Locktite" and in a pinch "crazy glue" works well too... FTI "crazy glue" can be rendered useless by heating it.

--.- Dave (who takes the C-182 down this weekend for it's "annual")

If you want it NEVER to move again, use the permanent grade of Loctite. Much cheaper than messing with any sort of self-locking nut and lots easier to get on, too. Only way to get it off is to heat the nut with a torch till it smokes. Used a lot of it on VW air-cooled flywheel gland bolts.

Stan

Speaking of aviation. Where does one find the nuts that can be "wire nutted" to the bolt. A shop where I do work needs some.

Bob AZ

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 likely work ?

the term is "lockwired" I've never heard of 'wire nutted'.

what is more often used is a castellated nut with a split pin through a hole in the bolt. this is used on hinge bolts.

what I think you are referring to is a hexagon nut is drilled through the peak of the hex from flat to flat. I have no idea how they actually do it without breaking drills. it appears to me to be the most difficult drilling I could imagine although thinking about it all the nuts done this way are brass so maybe it is easy with a jig.

what is often done is not to bother changing the nut but to create a washer with a lobe. the lobe has a hole through it and is bent up clear of the underlying surface. the lobe is lockwired to something. on the washer you bend a section or two up onto the flat of the bolt. something like this is used on marvel schebler carburettor bodies.

there is also the method used on a glider I know. the counter weight is screwed on to a support. both pieces have opposite side flats. a washer is used between them. one side is bent up, the other side bent down.

if none of these work for you describe the application more fully and I'll try again.

Stealth Pilot

of course dave but the quoted part above is a description of what Nord-Locks do best.

a round nut with no flats could do this perfectly.

======== common on race vehicles. jigs are commercially available.

see

Unka' George [George McDuffee]

------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).

There are also castellated locks for standard nuts. They go over the existing nut and get pinned or wired in place. Used to see them a lot on front wheel bearings.

Of course if the OP actually means that once installed he will REALLY never need to remove it. Tack it with a welder.

Thanks for the additional replies guys, and thanks for the links to that nut fixture F. George Mcduffee.

Tacking with a welder may be an option at some point. I could drill through both the nut and bolt after assembly and put a roll or spring pin in there, but something about doing this after the unit is already assembled did not appeal to me.

If I use a set screw in the nut as mentioned above, can I drill and tap the nut for a set screw before it's threaded onto the bolt, or will I have no choice but to do it after assembly (I'm thinking the cris-crossed taps might cause a problem with threading the nut onto the bolt) ? If I have to do it after assembly then a roll pin would be better.

It could be that a standard locking nut will work. The nut and bolt rotate together as one unit as the bolt is rotated to adjust a slider. There is not much axial force on the bolt during adjustment but the loads increase when the device is in use. There is a Delrin washer under the nut so as long as the friction between whatever is locking the nut to the bolt is greater than the friction between the nut and the delrin washer due to bolt rotation, then the nut should never back off. It would only tend to back off in one direction of rotation anyway as the other direction would tend to tighten the nut. If I have to use a steel washer at some point, then I may need a stronger bond between the nut and bolt but even then it seems a locking nut may work.

It seems that the consensus is that the distorted thread type lock nuts have the greatest resistance to removal.

John

I agree.

in aviation practise a bolt which forms a pivot is always used with a castellated nut with a split pin. ...thats the mantra.

on my tailwheel is a link rod with two ball ends. since these pivot I used castellated nuts, drilled bolts and splitpins. ...and needed to replace them about 4 times a year. the threads were forever stripping out.

I replaced the bolts with undrilled bolts and used deformed thread nuts (they are an aviation nut for application in areas subject to heat that would melt the nylock). it turns out that these nuts have over twice the thread length in them in comparison to nylocks or castellated nuts. in 4 years I've never had to touch or replace them once.

the mantra isnt always correct.

btw you will get best results using them dry. Stealth Pilot

There are those of us in aviation design that feel saftey wire only holds the broken parts together. I can show pretty easily that the tangent load associated with the torque to remove a nut is much grater than the tensile strength of the wire. My feeling is that if there is enough energy in the system to make the nut back off (vibration, rotation frictions, etc.) then there is more than enough energy to break the wire.

The FARs require any bolt in flight control systems which is subject to rotation to be retained with at least two means of retention, one of which must not be friction. Practically, this usually means a castilated nut and cotter pin. The problem with this arrangement is that by definition you loose the primary retention method of the design - namely the tensioning of the bolt-nut assembly to near it's yeild strength.

If possible you are always better off revising the design to ensure the bolt is not subject to rotation and then use the deformed thread self locking nut for the secondary means of retention.

my $.02

For what you seem to want to do, best options (decreasing security, increasing ease)

Weld it.

Braze it.

Solder it.

Use the SERIOUS Loctite on it. Back in the 1980's that was "red" .vs. "blue" but they have many more products now - but they presumably still make several that are really, REALLY difficult to remove, requiring heat, etc. - use one of those.

Lock nuts don't compare favorably in effectiveness.

--Um, here's another approach:

On Thu, 24 Jul 2008 17:44:24 -0700 (PDT) in rec.crafts.metalworking, John2005 wrote,

Ordinary nut. Leave about 1/2 bolt diameter sticking out past the nut or cut it off at that length. Peen over the bolt end with a ball peen hammer to form a round rivet head. No wrench is gonna take that off.

On Thu, 24 Jul 2008 17:44:24 -0700 (PDT), with neither quill nor qualm, John2005 quickly quoth:

In my experience, the nylock nuts (#1 in your list) are destroyed by running them more than about one thread's worth past the nylon. They work fine on the far end of a thread only.

Top/center-distorted nuts (#3,4) provide some extra oomph, but also wear down if they're run very far down the thread.

Expanding head locknuts (#2) don't wear out as quickly as the top two but also don't hold as tightly.

None of the above put up any real resistance at _all_ to removal with a standard wrench. I won't use the top two at all in automotive work and am amazed that the aircraft industry allows them (expanding the thought behind Stealth Pilot's reply to you.)

If you want easy installation in addition to moderate resistance to wrench removal, use a blue Loctite like #246. (See McMaster catalog page 3326) It takes a concerted effort to remove or change a Loctited nut's position.

If you want easy installation in addition to severe resistance to wrench removal, use a red Loctite like #262. (same page) It takes _heat_ and tools to remove a nut.

IOW, if a wrench is involved, none of the four you discussed is worth a hoot.

If it were vibration you were worried about, a friend who owned and raced a Husky 400 motorcycle used Loctite on it. That bike was so powerful and vibratory, even the blue Loctite failed. Only the red worked for him. I rode that jet once and it scared the shit out of me. The throttle was damnear a toggle switch with a jet engine connected to it. I pinched several buttonholes in my skivvies before I got the reversed throttle turned the correct direction and got my feet back on the bike. It was some heavy metal, man.

-- Imagination is more important than knowledge... Albert Einstein (1879 - 1955)