Thread Question

[st@rk]

I’ve got an engineering question for you guys; hopefully you or someone you know will have rule or an equation to calculate this!

There are five wheel studs on my car with M12x1.5mm pitch threads.

The nut shown in the attached image is 29mm deep, but you'll see that the thread stops before the end of the nut, so the actual thread depth is 26.5mm deep.

Once the wheel is on and the nut is fitted and torqued to 110Nm the contact depth of the nut thread on the stud is only 20mm / 13 threads as the stud then ends and the rest of the nut sits ‘off the end’ of the stud.

Without knowing the different grades of steel used, can you determine what the minimum number of threads the nuts need to be on by?

Hopefully this will be less than 20mm / 13 threads and definitely less than 26.5mm / 17 threads or the nuts aren’t right either!

 

[APEowner]

With an educated guess on the material of both the studs and the nut that can be calculated but best practice and every motorsports sanctioning body that I'm aware of calls for the threaded portion of the stud to extend past the nut.

 

[astroracer]

Basic rule of thumb is 1 1/2 x's the thread diameter to attain a viable thread engagement. 1 1/2 x 12 is 18 so your nut covers the basics. If you are still worried about it get longer studs but you are probably good to go here.
Mark

 

[rlitman]

Basic rule of thumb is 1 1/2 x's the thread diameter to attain a viable thread engagement. 1 1/2 x 12 is 18 so your nut covers the basics. If you are still worried about it get longer studs but you are probably good to go here.
Mark

That's a start. More thread engagement is required for die cut threads, less, for a rolled thread stud (what you have here).
Similar issues with percent of thread depth in a tapped hole. Again, this nut and stud are in pretty ideal conditions, and I'd think you have plenty of engagement.

Think of it this way, how much thread engagement would you have if that were just a hex nut? Basically, no more than the hex surface. And a hex nut has plenty of thread engagement with a rolled thread screw to snap a screw in tension. You're already going past that level of engagement.

 

[Raymond Fast]

I saw it calculated once by a guy with an MIT masters in mechanical engineering (a very long time ago) and couldn't possibly remember the formula now, but what he proved was that after the first five threads engage, the benefit of any additional thread engagement is practically negligible. That is regardless of materials, fastener diameter, or thread pitch or type.

 

[Raymond Fast]

... Yummy Cream filling keeps oreo halves from torquing off as required. ...

I would not recommend trying to mount a wheel onto a hub with yummy cream filling, however. Well, maybe if it came from a Hostess ******* ... but I don't think the middle of an Oreo cookie would be strong enough to hold.

 

[MoonRise]

Engineering answer: You are 'fine'.

Only the first 3-5 threads engaged do 90-95%+ of the 'work'.

However, it's usually considered 'good form' to have the male threads go 1-3 threads past the end of the female threads of the nut. Usually so that at a glance, one can see if the nut is actually 'tightened' or not (not technically 'tightened', just whether it was even 'mostly' installed onto the male threads or not).

Also, generally you want a blind threaded hole (not what you have here) to have a minimum threaded depth of 1.5x the thread diameter. Sometimes, for very large tensile strength differences between the hole's parent material and the fastener material (UTS of say 20 ksi for the hole, like some 'soft' aluminum, and a high strength steel bolt like maybe a 200 ksi Bowmalloy bolt, stronger than a Grade8 bolt) and a thread insert like a Helicoil, you might go up to 3x the thread diameter as the minimum threaded depth of the tapped/threaded hole.

A bit 'sloppy' to me having the stud end recessed in the lug nut, but 'ok' strength wise.

 

[st@rk]

Thanks everyone for your help; its much appreciated!

 

[kerrynzl]

I’ve got an engineering question for you guys; hopefully you or someone you know will have rule or an equation to calculate this!

There are five wheel studs on my car with M12x1.5mm pitch threads.

The nut shown in the attached image is 29mm deep, but you'll see that the thread stops before the end of the nut, so the actual thread depth is 26.5mm deep.

Once the wheel is on and the nut is fitted and torqued to 110Nm the contact depth of the nut thread on the stud is only 20mm / 13 threads as the stud then ends and the rest of the nut sits ‘off the end’ of the stud.

Without knowing the different grades of steel used, can you determine what the minimum number of threads the nuts need to be on by?

Hopefully this will be less than 20mm / 13 threads and definitely less than 26.5mm / 17 threads or the nuts aren’t right either!

For piece of mind, I just measured a normal tapered style lugnut that was metric 12mm x 1.5 pitch
The total height was 16.5mm plus you need to subtract about 1.5 x 2 for the countersunk on both outer edges

The lug nut you pictured should also be threaded in the shank [a common European practice]

 

[wingnut_1]

I agree with everyone that recommended 1-1/2 times the diameter. I was taught and all of my life used 1-1/2 to 2 times for maximum strength in my design and building of automation machines in manufacturing. Anything above that is negligible

 

[lakeroadster]

http://www.engineersedge.com/calculators/iso-minimum-thread-engagement.htm

 

[laser3kw]

Only the first 3-5 threads engaged do 90-95%+ of the 'work'.

most correct.
the 1-1/2 x yada yada is a farm rule of thumb. It works and keeps most applications out of trouble, sometimes by dumb luck.
There are many more variables that are formulated into the fastener equation.
Just take a look around your vehicle and see how close that rules is followed.

 

[gearhead1]

I've used 1xdiameter in steel, 1.5x in cast iron, and 2x in aluminum. I'm an engineer also, and as others mentioned, I fully agree that the first few threads 'do the work'.

Assuming it was designed right to begin with, if you have the stud flush with the end of the nut or past it, you should be fine.