Half nuts

[WolfieParticipant @wolfie]

[WolfieParticipant @wolfie]

OK as I understand it, half nuts are simply there to tighten up against a normal nut to stop it shifting. So whats special about a half nut? Can’t another normal nut do the job?

 

[_Paul_Participant @_paul_]

Normally half nuts are what is used to operate/move the carriage on a lathe when screwcutting they clamp around (depending on type) the leadscrew.

 

Do you mean “locknuts” like Nylock or it’s predecessor the Symonds nut?

 

Regards

 

Paul

[WolfieParticipant @wolfie]

I mean half nuts, a bog standard nut but a bit narrower

[KWILParticipant @kwil]

Yes, but we will now no doubt get into the argument whether the half nut (or additional full nut if you wish), should be over or under the main nut!

[Ramon WilsonParticipant @ramonwilson3]

Ah, Kwil, I was waiting for that.

 

When I read the original post I could only think of that movie ‘Pan’s Labyrinth’ and the scene where the girl eats the grape and ‘awakens the monster’

 

Well it’s not going to be me

 

You’ve done it now Wolfie

Ramon

 

 

 

 

[JonParticipant @jon]

Posted by Wolfie on 26/12/2011 23:08:11:

I mean half nuts, a bog standard nut but a bit narrower

 

They are called ‘thin nuts’ sole purpose is to act as a lock nut.

 

As above half nut is for engaging and diengaging lead screws used for threading.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Wolfie, yes another normal nut will do the job of locking a nut to stop it coming loose. The reasons for using half thickness nuts are varied, but basically, when buying several hundred they work out cheaper, add less wieght and of course you don;t have so much sticking out, so your stud/bolt can be a bit shorter.

 

The half thickness nut goes on top, this was mentioned in the “Metric Taps” thread.

 

Regards Nick.

Edited By Nicholas Farr on 27/12/2011 00:20:37

[John McNamaraParticipant @johnmcnamara74883]

Hi All

 

If a full size nut is used as a lock nut on top of a same size nut clamping a bolt or stud that uses the lower nut to clamp a member, the lower nut will most likely not be holding the load. the upper nut will press down on the lower nut disengaging the threads as the stud bolt or stretches, passing the load to the upper nut.

 

Not desirable as it increases the effective length of the fastening, allowing more spring.

 

If however a thin nut is used there will be less threads engaged in the thin nut. Provided the tolerances of both nuts are the same. the thin nut will expand more radially and be unable to disengage the lower nut (if it is properly tightened) from the bolt or stud; while firmly locking it in place.

 

Cheers

John McNamara.

Edited By John McNamara on 27/12/2011 05:10:53

[Gordon WParticipant @gordonw]

I agree with John above. They mostly seem to be used by scale modelers of steam stationary engines and the like, in the old days the two nuts might have different hex sizes.

[WolfieParticipant @wolfie]

OK I knew there had to be a reason for it cheers.

[Francis SykesParticipant @francissykes95134]

For what it’s worth, and I didn’t think it was clear to me reading the top posts, there are two meanings for half nut:

 

i) – the locknut that is spoken about above (effectively a half height nut)

 

ii) The split type nut found most often in a lathe saddle to clamp onto the leadscrew. It is two half threaded pieces. A quick google image search brings this up straight away for anyone trying to visualise.

 

I know the poster wanted the lock nut variety – I was surprised by the dual meanings of this word in the same subject – I can imagine a ‘fork handles’ type sketch with a storeman asking for a half nut…

[Nicholas FarrParticipant @nicholasfarr14254]

Posted by John McNamara on 27/12/2011 05:07:48:

Hi All

 

If a full size nut is used as a lock nut on top of a same size nut clamping a bolt or stud that uses the lower nut to clamp a member, the lower nut will most likely not be holding the load. the upper nut will press down on the lower nut disengaging the threads as the stud bolt or stretches, passing the load to the upper nut.

 

Not desirable as it increases the effective length of the fastening, allowing more spring.

 

If however a thin nut is used there will be less threads engaged in the thin nut. Provided the tolerances of both nuts are the same. the thin nut will expand more radially and be unable to disengage the lower nut (if it is properly tightened) from the bolt or stud; while firmly locking it in place.

 

Cheers

John McNamara.

Edited By John McNamara on 27/12/2011 05:10:53

Hi John, I’m sorry I can not agree with you. Firstly to achieve this you would have to tighten the lock-nut up to a greater torque than the load-nut, and secondly you would not do this, and further more in my life time of using nuts and bolts most every day in industry and the many hundreds of times I’ve used two nuts of the same thickness and rating, I have never experienced this situation.

 

It is worth reading Tubal Cains artical “Bolts, Nuts and Screws” in ME vol 140 issue 3500 pages 1069-1073.

 

Regards Nick.

Edited By Nicholas Farr on 27/12/2011 11:10:18

[John McNamaraParticipant @johnmcnamara74883]

Hi Nick

 

I have always placed the thin nut on top with good results; There is evedence here that it should be on the bottom.

 

There are two trains of thought. Good Wiki….

 

NASA reference see page 7….

 

Thin nut on the bottom watch the videos

Found Here….

 

From reading the text the tightening sequence is very important.

More homework is required.

 

From memory I read about it (Thin on top) in a text Fundamentals of Machine design by P Orlov (USSR translated to English 4 Vols) I will dig it out and read up.

 

Cheers

John

 

 

 

 

[Ian S CParticipant @iansc]

It’s not long since we had a discussion on this subject, I mentioned how Continental aero engines solved the problem of where the lock nut goes. The cylinder base is held to the crankcase by long through bolts(horizontaly opposed engine), with plain nuts, and PAL nuts on top, these nuts are made of sheet metal about .010″ thick (?) , the hex is folded up to take a spanner, these nuts are lightly tightened down after the cyl base nuts have been torqued. They don’t look much, but they seem to work. Ithink they have been around since before WW2. A similar/ same nut is often found, on its own holding switches and pots in radio gear. Ian S C

[Gordon WParticipant @gordonw]

If the top nut is torqued more than the first (bottom) nut and thus takes the load of the bottom nut, isn’t this the same as using a washer?

[KWILParticipant @kwil]

Even though the top nut is taking the load, they are still “jammed” together, the bottom nut is not free to turn like a washer.

[Ian S CParticipant @iansc]

Some times if something is required to swivel on a bolt, the nut can be screwed down lightly then the lock nut taken down, and the bottom nut bought up against the locknut.

You can also use that system to fit and remove studs. Ian S C

[Author]

Posts