ALFAGTV6.COM

I spot cut threads!

Personally I would not use cut threads for any high load screws, certainly not the wheel studs.

Mats, in the wheel stud photo the stud of the left is cut, but the one on the right is rolled. Is that correct?

Yes.

Hi Mats,

you got me a bit puzzled...i just spoke with JK by the way and i would also like to know the difference between the two types of studs as far as possibility of fatigue failure is concerned....

By the way, this is an everyday car on street tyres (if that is of any importance...).

X

I just did a search on the cut/rolled thread issue...ok, I do know a lot more now, mainly from C.Smith's book on fasteners; great info. 'X's car is not a track car and never runs slicks, but still, a relative comparison of the two thread types regarding strength would be informative at this point, even if it would only help X feel more confident.
Jim K.

When you cut a thread you will create a groove around the circumference of the screw-to-be with a knife edge in the bottom. A rolled thread will have a small radius, it will also be "forged", the material will shape itself into the outer surface of the thread instead of a bar stock being cut to size. The transition between the round part end the tread is also less abrupt. Look at the picture above and see how the thread is gradually going from fully developed to round in a length of material instead of just suddenly appearing.

Motivation enough?

A rough estimate a cut thread is ~70-75% in strength of a rolled thread.

So i should start worrying i guess...

X

Maurizio wrote:A rough estimate a cut thread is ~70-75% in strength of a rolled thread.

Yield, once?

What about fatigue?

The shape of the bottom of the 'V' in threads can be changed by the machinist at will. Those threads may be cut with a die and most have a sharp "V" shape.

The biggest strength problem I see on the stud is that the thing is made with no heat treat=grade 3 or less. I thought wheel studs were supposed to be at least grade 5 and more commonly grade 8.

What is the reason for the longer studs? If its to run spacers I'd get different studs. If its to make a longer reach thru a thicker wheel and that wheel centers on the hub without an adapter ring I'd think it would be useable.

If necessary buy a longer stud without the flat on one side of the rim and grind that flat yourself. Also, if the unthreaded portion of the shank sticks out a bit too much its ok as long as the nut will tighten correctly.

hth,

Thanks for the info.

Reason for longer studs is to fit 8mm spacers for the 4x98 Ronal Turbo wheels with which it seems i have some kind of fetishism...

Any way, it rather turns out that the CNC machined studs idea was not the best one...

I should dig into that Demon Tweeks catalogue again.

X

Mats wrote:Yield, once?
What about fatigue?

Yep, a bit to short through the corner.
I'm talking fatigue here, have done some rough estimating fem calculations in the past.
That was a comparison of just geometries.
Material and grain restructuring from cold deforming even not taking into account .

Not on the topic of rolled threads but here are some classic auto delta double caliper hubs. that have lugs welded to for ap calipers.

There was a guy btw, who was selling these exact double caliber hubs (NOS) in E-bay a couple of days ago for about $2.000 if i remember well...

X

These are definately not for sale. I must measure the bottom balljoint to centre hub to see if they are same dims as SZ. These were brought into SA in 1982 for touring car champs.