I have been asked to modify some M16 stainless steel A4 caphead setscrews to be used as car wheelnuts. The plan is to drill and tap M12 fine in the plain (16mm diameter) portion of the bolt to create a 'sleeve' nut.
My concern is not knowing whether the aproximately 2mm wall thickness of material left will be sufficiently strong enough. The intended use is on a 'show' car but will be driven (carefully) on the road.
I would not know where to start calculating, and even if I could I would not know the values of whatever forces are involved.
I totally concur with your remarks. The car however is a nearly new £60K+ model which has been substantially modified (lowered, lightened etc (for aesthetic rather than perfomance purposes) to such an extent that the wheelnuts come a long way down the list!
Depends on whether you wish to be involved with failure and possible consequent responsibility. SS socket head nuts of those dimensions aren't going to be adequate on the road use.
Well I'll probably get flamed for daring to mention regulations 8-), but won't this car have to go through the Single Vehicle Approval before it can hit the road?, maybe he should be looking into the implications of that and what attitude their inspectors take to home made running gear. My gut feeling is also that there's no way you should tinker with the things that hold the wheels on!.
You really have a peculiar way justifying a dubious mechanical alteration.. Cars don't move without wheels, however if they are moving and the wheels fall off, there can be very dire consequences.
If the vehicle does not fall into the SVA category (I doubt whether this one would) then the owners responsibility is to inform the insurance company of any modifications from standard (which he does). The car is fitted with many after market 'modding' bits including commercially available adaptors that convert the wheel fixing bolts to a different PCD. These adaptors are (well) made in umpteen variations but the manufacturer has no control over what the customer uses them for but I would imagine that incorrect use of them would be more dangerous than 'home made' gear.
In this case the owner is a responsible and sensible person who wants a particular 'look' to a car that will do 100 miles a year.
Perhaps subbing this work out to a motorsports engineering workshop would acquire a guarantee that the nuts are safe to use?
They should have the necessary expertise to advise on this.
There must be many companies that do work for competition cars.
The sad incident yesterday on the news, where the car spun into 12 cyclists killing 8 of them comes to mind. May be wrong on the figures here but it was a terribly tragic accident.
2mm of wall thickness sounds to be too thin to me, if asked to do this I would advise passing the work onto someone who would normally make wheel nuts.
DON'T Reasons... bolts on the pasenger side tend to self lousen... there are tricks played with wheel fit and seat to prevent this...
If the nut is not the correct length.. short it alows a bending stress on the stud... Long and it tightens on the base and leaves the wheel louse.
If it's not a good fit in the hole in the wheel the wheel will move, ... My tube nuts are less than 0.02mm under the hole size in my alloy wheels.
Even if the nuts are right, if the vehicle has been modified with such an unusual set of wheels that proper nuts are not available are the studs O.K..... ( take a look at the rules for spacers on race cars.... ).
If the people asking for these nuts can't make them themselves they are not likley to know that what they are asking for is safe to use.
As the stud is probably high tensile steel and a rolled thread it will probably be 20 to 50% stronger than the stainless steel nut with a cut thread in tension.
Correct torque for a stainless nut with a cut thread assembled on a rolled steel thread stud would be a matter of gess work.
Please notify me when and whare this vehicle will be on the road... I want to give it ( and the wheel ) a wide berth :-)
Oh I misunderstood, I thought it was some completely custom job. It sounds as if it falls into the same category as me converting my Transit into a camper, all I had to do was find an insurer who would accept the changes and notify the DVLA of the swapped engine. I ended up using a kit-car insurance specialist in the end as they understood.
Peter is absolutely right here, it's a big can of worms to open. But - if you still decide you want to go ahead and do this you really need a frame of reference to start with. For instance, what was the UTS of the original wheelnuts (unmodified car) of the to start with? Closely followed by, what is the original UTS of the stainless hex bolts you propose to use? Followed again by what grade of stainless are they? Some stainless Steels have a low yield strength and will fracture easily, although this may be increased by the cold working in machining it, whilst others may have a greater elongation before they fracture. Both are failure modes which are not attractive for the application!
In my opinion you would need to at least match if not exceed the strength of the standard bolts/nuts. Normal structural carbon steel bolts in the ISO standard are designated 8.8 on the bolt and have a UTS of 785 n/mm2, although wheel nuts may well be specced higher, so the stainless grade would have to match this in both spec and cross section after machiningto be safe. I know you have said it is only a 'show' car, but as long as a bloke has bo*****s swinging between his legs there will come a time when he will floor it and maybe do an e-stop or two, and I would hate to be the one to make a bolt that may break in these circumstances.
FWIW I had 3 out of 5 wheel bolts break on one wheel of my Disco 2 years ago whilst traversing the Route Napoleon with the family, and this was a bit of an underpant-changing-moment. It happened after fitting a set of TUV tested and approved wheel spacers, so be careful!
You can buy plated wheel nuts and other fancy wheel fitting accessorie
at most custom wheel shops. I'd thumb through their catalogue befor risking it because you just know that if something unfortunate happen involving litigation, your clients will put you in the frame as quic as anything. Is it worth it for a forty quid pocket money job? The mai reason that the male threaded parts of the bolting system are hig tensile is not only because of the shear strength and impact resistenc of the stud but because the thread is liable to be peeled off away fro the core. Nuts by contrast can be regular steel because the threads ar in compression as the forces try to strip them. For that reason interna threads are stronger than male threads when made in like for lik materials. Sleeving up a thread in stainless steel introduces a mal thread into your equation made from inappropriate material and not eve attached to the core. The high tensile core might be adequate to resis any shearing forces via torque through the wheels but the risk o losing a wheel nut through thread stripping is a real possibility Apart from the aircraft industry, the car industry is subject to mor stringent rules and regulations regarding engineering safety than an other industry and that's for a reason
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