Maximum torque for M24 nut onto hollow threaded shaft

[johnpearcey]

Someone already posted a similar question back in 2009 but there were no replies. I also need this information, i.e. how can I work out the maximum allowable torque for an M24x1.5 nut onto a threaded shaft. The shaft is hollow with an internal diameter of only 20mm.

[Kelly_Bramble]

Here's what I would do to estimate the maximum applied torque:

Determine which feature is going to yield first – the thread or the wall section of the threaded feature.

If the thread feature is going to yield first..

Determine the effective thread shear area of the case you're analyzing.

https://www.engineersedge.com/thread...s_area_iso.htm

Determine the thread material yield characteristics. -

Using thread shear stress equation – or whatever is most correct determine the applied perpendicular force at the yield strength.

https://www.engineersedge.com/materi...ear-stress.htm

Then, using the generic force vs torque equation, algebraically determine the maximum torque.

https://www.engineersedge.com/calcul...orque_calc.htm

Torque related equation and calculators:

https://www.engineersedge.com/fasten...ead_menu.shtml

[PinkertonD]

Hi John,
You don't state you technical knowledge and skill levels, so forgive me if this sounds like I am talking down to you a little.

As Kelly suggests, find which is the weakest part, the threaded tube or the nut.
To do that for the nut, calculate the distance from the root of the thread to the center of a nut-flat.
To do that for the tube, calculate the distance from the root of the thread to the perimeter of the 20mm inner.
If the two parts are the exact same material then the weakest will be the one with the shorter distance. Roughly, but near enough for this.
If not the same material, then find the relative tensile strength for each and calculate the failure point for both cross section area.

Once there, proceed as Kelly suggests, but also make sure that the tensile yield point (elongation) is not exceeded.

A 24mm anything is a pretty substantial "bolt/nut" combo so I am guessing working-loads could be high. There are other variables that may come into play like vibration, flexing loads when working, thrust-loads, rotational issues etc. Not a simple process and if it is for some important equipment, you may want to consider hiring an Engineer to do it for you. Tightening to max-torque is a risky approach and you may want to investigate alternative methods of locking the nut in place.