corrado33

You've got a point.

If I have some time, I'll throw the problem into solidworks and see what bends first, threads or axle when a clamping force is applied. Although I don't know if I can run analysis on threads.

restlessswind

Every time I check the play on a brand new, pre-assembled bike, the front wheel bearings are too tight (uncompressed by skewer). This bugs me. I have to make the fine adjustment myself. However, what is the REAL consequence? I've bought may used bikes that have never been serviced, and after servicing tight hubs myself, the bearing balls and cups seem to mesh perfectly time and time again. So my conclusion is that the fine point of splitting hairs of engineering physics (perfectly adjusted vs slightly loose) is really not much of a concern on common bicycles. Just saying. Do as you will.

RubeRad

This is a very-commonly-reported experience. I guess the consequence is that when clamped the bearings are too tightly binding in the races, and there is unnecessary friction, and probably some grinding.

restlessswind

I agree, but my point is that a properly adjusted hub vs slightly loose for QR bow is nothing to really worry about as compared to most pre-assembled hubs.

Robert P

This guy was the bike store's head mechanic.

u235

Slop/play/tolerances in the threads on the nuts and axel. When the QR and associated spacers get force on them, it compresses the entire assembly and compesses the hub bearings. I've never tried it but if the 5mm spacers we're threaded or there was a nut on the inside of the dropout on the axle instead of a spacer, I bet that would not happen.

Doug64

+1

Look at Park Tools' website at "hub adjustment". That is essentially how they recommend adjusting the hubs. I use a 10 mm box end wrench instead of a nut, but it is the same technique.

Rowan

What a crappy comment to make. Actually, I haven't needed your help. I can strip, clean, and reassemble bicycle hubs very well, thank you, and have been doing so for around 20 years.

I AM, however, interested in the reasons why, and especially when a popular and seemingly knowledgeable source of bicycle information, the Park Tools website, alludes to the fact that flex in the axle is what causes the bearing surfaces to move closer together, not compression.

So far, only 79pmooney has provided some useful calculations. Thanks.

Maybe you should go away, and peform the experiment that I suggested earlier.

Tape2012

Think about it. The only difference between an axle compressing or bowing under load is whether the compression is uniform around the circumference of the axle. As a practical matter I am sure due to many factors that the compression is never perfectly uniform, so some small amount of bowing would be expected. But as stated before, there is plenty of play in the threads that any bowing would not affect the bearings.

Your example of squishing a straw is irrelevant, as that would simulate stressing the axle past elastic deformation and into plastic deformation. Of course if you stressed the axle that much it will buckle, the material has to go somewhere.

If you want a trained monkey, you got to at least feed me peanuts.

Rowan

OK. I am going to let this go. That will make you happy. Of course, I say this because the irrefutable Jobst Brandt said it's compression, although he regarded that as piffling when compared with the forces applied by the chain and rider. I wasn't a fan of Brandt's, but everyone else took his word as gospel, even Sheldon Brown. So there it is.

The essential thing I have got out of this thread is the method. The reason is almost irrelevant. I have a spare axle set downstairs. I might play with it. That way I don't have to pay anyone for my curiosity.

joejack951

You'll likely need a more powerful FEA suite than Solidworks for that. Do you have their full FEA package that works on assemblies? What do you do with Solidworks (asking as another curious SW user)?

Kopsis

One of the first things an engineer learns is how "imprecise" natural language is Does "compression" mean a change in dimension due to the application of force (spring compression) or a reduction in volume of the material (gas compression)? In this case it's the former and the mechanism is radial bowing of the unsupported hollow axle. This isn't linear bowing (i.e. bending, which is what most people think of when the term "bowing" is used) but bowing in the sense of the shape of an old wooden barrel (greater diameter in the middle than the ends).

Metaluna

You could also use fender washers where the I.D. is just barely large enough to pass the skewer through, so that they sit on the ends of the axle, rather than slipping over it and pressing against the locknuts. Then when you close the skewer you're only applying force to the axle itself.

My J. A. Stein Hub Axle Vise works this way on one side, but the other side still presses against the locknut. I have however observed some effects when using this device that might support your theory.

corrado33

In all honesty I don't use SW very often. I have access through my university and I've used it to design and test a few scientific apparatus here and there. I've also briefly worked at a machine shop that used SW.

I also used it for some rudimentary gas flow simulations to make sure the gasses didn't eddy anywhere. Of course, I can't say exactly that I "know what I'm doing." Although the program itself is easy enough to figure out.

skoda2

I agree, have been wrenching bikes for 40+ years, and always properly adjust hubs(no play), and don't worry about the QR compressing the axle. IMHO the thin QR will elongate before the hollow steel axles will compress. My two cents.

hueyhoolihan

spoken like a true engineer!

attacking the integrity of the question and clouding up everything with facts.

and BTW, when you say 'dimension' are you talking about heighth, width, depth or time?

Kopsis

Hmm ... hadn't considered the effect of compression in the time dimension. I'm not a strong enough rider to see relativistic effects

Now, a "seasoned" (i.e. old) engineer would skip the FEA software and take the problem now phrased in precise mathematical terms and see if it passes a sniff test. In other words, how much bowing would be needed to appreciably compress the axial dimension. If we use a 130mm OLD as the length and assume we need a 0.010" reduction to see much effect on the bearing, a simple arc length calculation shows that the axle would have to bow out by nearly 3.5mm in the middle to shorten the axle that much.

So my money is with the "thread slack" advocates.

u235

Put a wheel in a vise and tighten it down on the axel ends. The wheel will still spin freely (up to a point where you physically start to damage the axle which is well past the force any QR can apply). Now clamp down against the spacers instead if possible instead of the axle ends and the wheel bearings will tighten up and start to drag. A QR and/or axle nuts pushes in on the stays simulating the exact process of what happens on the later.

I don't have a vice that can hold a wheel that way but you can simulate this in other ways.

AndreyT

You misunderstood something.

QR never "compresses the axle" and no one ever said that neither here nor in any article. (Moreover, QR force actually works to stretch the axle, not to compress it.)

What QR "compresses" is the cone nuts. Regardless of how precise the axle/cone threads are, there will always be certain amount of play in these threads, allowing the cone nuts to "rattle" in and out a little bit when not loaded. As the cones are tightened on a free wheeel, the bearings push them outwards in their threads. The QR "compresses" them inwards. This play between the "outwards" and "inwards" positions of the cone nuts is what's taken out by the QR pressure.

This cone nut play is indeed what to be considered when adjusting the bearings. This is what's usually mentioned in various posts and articles, not some mythical "compression of the axle".

wphamilton

Well I'm saying it so it's not "no one". We put pressure against both ends of the axle, so it compresses. The shaft of the QR stretches. How much from a given force, depends on how much metal is pressed and a quality specific to metal.

Yes, there's got to be some "give" in the threads, and the cones are pushed in.

maddog34

like i said MUCH EARLIER in this hilarious thread... the THREADS are the weakest point, and they deform.

The force required to compress an axle is TREMENDOUS, and no quick release will do that enough to change the overall length of a bike axle, PERIOD.

Park said what they said to SIMPLIFY the concepts involved.... "dumb it down", so to speak...

look into thread contact sometime.... and also look at a threaded surface under extreme magnification....very little interface of material is realized. We bike wrenches are dealing with Deformation of THREADS, not AXLES.... and the "Engineers" responding are mostly book-learnt idiots with calculators, not wrenches and experience.

over-tighten a QR on an axle... examine where the failure occurs.

makes yet another batch of popcorn... bring on the clowns! make sure to use a dead language when describing your fallacies.

maddog34

ok, kids... schoolin' time... note the radius at the bottom of the thread valley? it's there for a reason.... it spreads out the shearing force that concentrates at the tighter radius areas of the materials involved.
https://gizmology.net/images/threadprofile.gif

NOW... what's "wrong" in this image, dimensionaly? the thread would not mate up well with a corresponding thread, unless the threads are cut to a too-loose tolerance, much like the cheap chinese axle sets are manufactured to...... Why?

look into "rolled threads", also... because MOST external threads we bike people deal with are ROLLED, not "cut with a die".

davidad

I just put an old style QR through a bare axle and it did not bend. It shortens due to compression and changes the bearing clearance.

Bike Gremlin

I've read, studied and practised bicycle mechanics, as a hobby and passion.
Have heard of Jobst Brandt relatively late in that process. Many of his conclusions have matched, or complemented mine, often backed by an (reasonably sounding and such that they can be tested and confirmed - not sure of the proper English word) explanation why it is so.

I find it hard to find (logical) flaws in his reasoning, while the little (mechanical) engineering knowledge I have leads me to believe many of his statements and opinions on bike mechanics are correct. "The Bicycle Wheel" being a book I'd recommend any bike mechanic, or engineer to read.

Tape2012

Wrong. If you don't believe elastic deformation occurs at relatively low pressures, step on your bathroom scale. If it reads your weight it is because metal is compressing and a variable resistor is measuring that tiny amount of deformation.

This is partially true. The contact area within the thread is relatively small and the initial elastic deformation will occur there first, but will eventually involve the axial dimension of the axle as forces equalize. I don't believe anyone here said that there wasn't some slop in the threads. But your assertion that all of the deformation occurs in the threads is just wrong.

The fillet at the bottom of the thread significantly improves the fatigue life of a bolt in applications such as engines. It does not significantly affect the strength of the threads, at least in the elastic zone that we are dealing with here. In a bike axle, the fillet has zero effect one way or the other.

Rolled threads are extensively used because they are much less expensive to manufacture and the cold working effect and the resulting grain structure of the rolling process produces a stronger thread.

I've spent a good part of my career teaching my maintenance guys the engineering involved in the equipment they are dealing with because it makes them better mechanics. The best are the ones who have a curiosity and want to understand why things are designed the way they are.