Wheel nuts should be expensive!

[xpensive]

Interesting parameter this "K", care to elaborate on that one JT?

[safeaschuck]

If we are talking coatings I believe (although I haven't scrolled back to check, have a look JT) that it was Xpensive that earlier mentioned the use of silver/copper coat on the thread which would make excellent sense for anti gauling no matter what the nut material, as for external coloured coatings, it is surely anti corrosive (suggesting ally) or for show and to make it easy to see the laser etch 'rotation->' mark.

Be it Ti or ally, the coating won't do much for the strength or life expectancy of the nut, although a surface coating harder than the parent metal would in most circumstances be useful on driven parts like this, it is not experiencing constant wear and it would have to be pretty thick to give the nut any increase in torsional strength? About the only advantage I can see is it might make it slide in and out of the gun easier and possibly help disengage any radial teeth like it seems the Toyota nut would require, if not it wouldn't be the first time something had extra money spent on it for the sake of it.

I can't believe we don't have an current F1 mechanic/machinist/fitter/draughtsman on here who's going to step up and say, I hand finished one last week, they are Ti (or ally) and they are screwed on tight. Come on, give us a clue! No one will find out!

[Jersey Tom]

K is a correction factor. Mainly I believe a function of surface friction and if your fastener is bare, coated, lubricated, etc. It does also wrap up some other parameters. Again, this kinda stuff is covered in any MechEng handbook under fasteners.

Regarding that coating, yea you can coat stuff like Aluminum but it doesn't last forever, and sometimes doesn't even do much. Coatings like that are typically ~0.0005"-0.0015" thick (0.01 to 0.04 mm). If you were to take a tomato and coat it with something hard and that thin, it just doesn't make as much difference since its so soft underneath. There's nothing to support it, particularly from impact loads. I've had a decent amount of experience with aluminum parts with metallic and anodized coatings.

I have a Champ Car wheel nut, same style as one used in F1, same coating even, along with a full hub sitting in storage somewhere. It is most certainly steel.

[xpensive]

A correction factor now? Try again!

[Jersey Tom]

A correction factor now? Try again!

This is simple stuff, man... feel free to look it up in Machinery's Handbook, the CRC Handbook of Mechanical Engineering, or any other.

Your K value wraps up friction, some geometry factors, etc.

I'm not makin this stuff up...

Edit - Just to make sure I'm not nuts I even looked this up in a textbook.

Machine Design (Rob Norton) ISBN 0-13-148190-8

Chapter 14 - Screws and Fasteners
14.9 Controlling Preload

T ~= K*F*d (F ~= T/K/d)

"K is called the torque coefficient. [...] the value of K varies very little over the entire range of thread sizes, as shown in Table 14-11"

Has nothin to do with engineering in imperial units.

[PlatinumZealot]

Yeah you are right.. K is a factor determined from experimentation.

He is right. It is used so that the Formulas can fit to actual.

It can be surface finish, hardness, certain sizes etc. I use it sometimes and I work in metric.

But Imperial still sucks..

I use it for simple everyday purposes but never use it to calculate. It is just too weird.


So it seems that steel is suited to the abuse of the impact wrench then? It has high impact strength, and it's life cycle is somewhat predicable.

[xpensive]

If we take things from the beginning, the mechanics of a bolt is far more complicated than meets the eye.

In a perfect world, friction-free, it would be very simple: F = (Torque * 2*Pi)/pitch of thread.

The influence of friction is rather complicated why diffent empirical formulas, including a friction and geometry-factor "k" (Kellerman-Klein), Torque-tension factor "Kappa", distribution of Force "Sf" as well as a whole heap of simplifications are used.

All in all, I guess you could make it as simle as "T = K*F*d", but you won't find it in my engineering office.

[safeaschuck]

DFT is always a safe bet

[Jersey Tom]

Oh for cryin out loud. We're talkin order of magnitude here. And that's about as good as you're gonna get in the pit lane.

In any event. The preload isn't my concern. The tensile strength of the nut isn't my concern. The point is aluminum threads are not very durable. Magnesium I think would be absolutely mangled. Don't think they'd hold up to the abuse of being run on and off the car with those impact guns and the torque they deliver. If your thread coating wears or chips off in a spot and the nut galls or cross-threads, your wheel is gonna be stuck and your race is over. Steel is where it's at, and the one that I own is pretty plainly steel.

Ti probably work as well, but I haven't played at all with Ti threads. Small weight benefit, but surprisingly enough even the steel nuts are relatively light just since the thickness is so low.

The end.

[xpensive]

First thing I learned at University was to understand what you do and learn how to prove it, taking formulas from books or manuals at face value is for high-school.
But since working overseas for longer periods of time, I have learned that this is not a universal concept.

I think tensile-strength is a minor worry, unless you are planning on exceeding yield stress of the material, where 6082 T6 Aluminium is OK for 280 MPa, at level with regular steel at 35% of the density. Thread-galling is a concern however, but somehow racing teams ans well as aerospace industry seem to make it work.

[humble sabot]

I'd be shocked, full-on shocked if it was 'regular' steel as you put it.
Reasons not least of which being that tensile strength is hardly the concern, and with alloys like Aermet at well over a thousand MPa yield you could make our famous nut all sorts of hollow.

[humble sabot]

I'm doing a bit of Flickr roaming in search of other wheel nuts from f1, and there certainly is a great deal of variation.

here's one that i'm certain is more costly than the SAG earlier in the thread, three parts at the very least, probably a couple specially made springs in there too.

http://www.flickr.com/photos/emohawk/27 ... 0/sizes/l/

id feel comfortable saying that this one is the aluminum equivalent of the first one seen in this thread.

http://www.flickr.com/photos/8771659@N0 ... 1/sizes/l/

and that regardless of alloy this one isn't aluminium

http://www.flickr.com/photos/79551934@N ... 7/sizes/o/

[Jersey Tom]

I'd be shocked, full-on shocked if it was 'regular' steel as you put it.

Well, again.. I have one. And it is steel. Next time I dig it out I'll have to take a picture of a magnet hanging from it. Same geometry, same coating as well. Can't speak for all of them across racing, but this one is steel.

Don't see why it's shocking. Steel is great stuff, even on pro racecars.

Yes, aluminum fasteners and threads work in certain applications, particularly if it's a one-time installation. NOT the best call if there is high-torque, repeated on-and-off assembly. Having worked designing and fabricating spaceflight hardware previously, I will say that even then aluminum threads were hardly ever used.. in favor of stainless fasteners and steel thread inserts.

[xpensive]

"Durability", eh? Interesting parameter that, can't find it in my material's handbook though?

I am sure that the CART-series had a rule against pricey nuts, just like they outlawed several other things.

Anyway, thanks for the pic's Humble. To the best of my understanding, they confirm scarbs' word that F1 wheel-nuts are made from a lightweight-alloy, Al or Ti, those look precision-cast at that.

[humble sabot]

I'd be shocked, full-on shocked if it was 'regular' steel as you put it.

Well, again.. I have one. And it is steel. Next time I dig it out I'll have to take a picture of a magnet hanging from it. Same geometry, same coating as well. Can't speak for all of them across racing, but this one is steel.

Don't see why it's shocking. Steel is great stuff, even on pro racecars.

Yes, aluminum fasteners and threads work in certain applications, particularly if it's a one-time installation. NOT the best call if there is high-torque, repeated on-and-off assembly. Having worked designing and fabricating spaceflight hardware previously, I will say that even then aluminum threads were hardly ever used.. in favor of stainless fasteners and steel thread inserts.

I didn't say i'd be shocked if it was steel, just that if it were 'regular' steel. That implies to me a quality of material that any F1 engineer would likely turn their noses up at. High end steel alloys are far and away a different class of material from your basic mild steel.