Another fastener question: why thru axles are used without nuts and washers?

[Maddie]

In that case just get a new derailleur hanger and add some middle strength loctite to the m4 bolts.

The stock nuts had a thread locker from the factory, unfortunately, it did not work.

You said the design of the derailleur hanger is questionable. That is rarely the case. But maybe share a picture or tell what bike we are talking about? I suspect something else is not right with your setup.

Also, m4 bolt with thread locker coming loose does sound strange. If unsure, take your derailleur hanger, degrease the threads properly and inspect for damage, get new bolts, degrease them too, let everything dry. Then add thread locker and assemble everything. The bolts won't come loose if done right. No need to add a second nut or anything. It doesn't add security but much rather increases the stress on the thread of the bolt itself as mentioned earlier.

[musiclover]

I was not able to find the pics quickly that were able to illustrate the problem explicitly. Here is roughly the dropout design. https://www.ebay.com.au/itm/322488097914

The dropout is put on top of the carbon frame and screwed onto the frame, rather than a design where a drop out is put inside a carbon "well" and is surronded by carbon.

Here is an example of a proper rear drop out design by the way https://www.lookcycle.com/au-en/product ... s-frameset

As opposed to poor design https://www.cyclingweekly.com/reviews/r ... -slr-9-2-2

[musiclover]

Also, don't know how common it is but the rear drop out is two in one with the derailleur hanger.

[tjvirden]

In that case just get a new derailleur hanger and add some middle strength loctite to the m4 bolts.

The stock nuts had a thread locker from the factory, unfortunately, it did not work.

Will the nut on a standard QR be improved by the addition of a second nut?

Isn't QR equipped with a preload lever? I thought it's design is different to a standard thru axle without the preload handle.

Addressing just the title first: "Why thru axles are used without nuts and washers?"

As has been mentioned, the threaded insert in the fork/frame is the nut. Tensioning the axle sufficiently (preload) prevents this system loosening, or moving excessively in normal use. There's no reason for an additional nut, nyloc, spring or otherwise; it's simply not necessary.

A washer at the lever/hex key end should be standard, to prevent any damage to the mating surfaces; every thru-axle I use has one, but that's because they all have a preload lever - the part that the lever acts against also acts as a washer.

Moving on to what seems to be your real complaint about a traditional 10mm rear dropout with a particular type of hanger.....

It has taken me a while to understand what you mean, but I think I do now.....

Also, don't know how common it is but the rear drop out is two in one with the derailleur hanger.

Is the hanger placed on the outside of the frame, or the inside? If it's on the inside, so that the hub axle sits directly on/in it then that will be the problem I suspect. Hanger on the outside is standard - a "two in one" hanger on the inside doesn't work as soon as you ride much (perhaps ok if you're really light). If your hanger is on the outside, then I think we'll need a picture to understand what's happening.....

Edit: I should make clear that this issue, for two-in-one hangers, affects traditional hubs (10mm dropout). As an example, Cervelo's thru-axle rear dropout/"nut"/hanger works well. It all depends on exactly how the dropout/"nut"/hanger is attached to the frame

[MikeD]

What is the difference of a normal bolt with two nuts and a thru axle with a spring washer and a nut?.. How do two nuts of the same thread pitch create a variable thread pitch?

It is putting excessive loads on the bolt threads. This is undesirable, especially in a system that sees lots of shock/impact/vibration.

How so? I don't see that. Double nutting is one way of providing thread locking. One example is the valve train of an automobile engine. Another is the bearing adjustment of my mountain SPD pedals, wheel bearings, headset lock nuts...

[ghostinthemachine]

What is the difference of a normal bolt with two nuts and a thru axle with a spring washer and a nut?.. How do two nuts of the same thread pitch create a variable thread pitch?

It is putting excessive loads on the bolt threads. This is undesirable, especially in a system that sees lots of shock/impact/vibration.

How so? I don't see that. Double nutting is one way of providing thread locking. One example is the valve train of an automobile engine. Another is the bearing adjustment of my mountain SPD pedals, wheel bearings, headset lock nuts...

Double nutting is useful on systems that rotate continuously and vibrate. A through axle doesn't. So sufficient end load/torque (think most are around the 8-10Nm level) on a 12mm thread should pretty much eliminate loosening through vibration, and precession isn't going to be an issue.

The boardman issue i've seen on two bikes, the thru axle nut seems to just "rest" against a face on the frame, held in place with two bolts. It looks like they've done a half arsed job of modifying a QR frame mould to take a through axle, and done it badly.

Every other frame i've seen, the through axle nut sits in a pocket and a flange/bolts are used to locate it.

All the through axles i have in the house right now have a retained washer/machined mating face on them, so no need for an extra washer.

And spring washers don't actually do what they are designed to do, they're a bit of a waste of time in a properly fastened joint (they might, possibly save you if you're terrible at following torque specs.)

[Cleaner]

All of this assumes that the bolted joint is correctly designed to carry the required loading from external forces.

The way that a bolted joint works is by placing the bolt under a tensile load (the bolt is stretched) when tightened to specification. This is preload on the bolt and it prevents the threads from unwinding while the preload is present. The torque spec is derived from operational external loads the joint is expected to see in service. The torque specification is a convienient way to ensure the correct preload is applied to the fastener.

Washers are typically used to distribute the compressive force under the head of the fastener thereby reducing the stress in the clamped material under the washer. If you are not plastically deforming the clamped material under compression by the head of the fastener then the washer will not increase the load capacity of the bolted joint.

If you are not familiar with the theory behind bolted joint design, the basics are addressed here.
https://www.boltscience.com/pages/basics1.htm

[musiclover]

The boardman issue i've seen on two bikes, the thru axle nut seems to just "rest" against a face on the frame, held in place with two bolts. It looks like they've done a half arsed job of modifying a QR frame mould to take a through axle, and done it badly.

Every other frame i've seen, the through axle nut sits in a pocket and a flange/bolts are used to locate it.

Yes, correct. What then happens is that m4 joint on the drop out becomes lose and the thread is being destroyed. Then there is no "nut" in the drop out and there is a need to use an external nut. (Or to replace a drop out).

[musiclover]

Some pics of the drop out design https://photos.app.goo.gl/Qn87EUFFgkPkeiFu7

[ghostinthemachine]

Yes, that's almost exactly the same as the ones I saw before. It's almost a perfect example of what not to do.

[musiclover]

Yes, that's almost exactly the same as the ones I saw before. It's almost a perfect example of what not to do.

Yes, terrible design.
Unfortunately, rear drop out design is not something most people look at when selecting their bike.

I wonder if this could be improved or fixed somehow (on this existing frame).

[ghostinthemachine]

All you can really do is rework the back end if the frame and bond in proper dropouts.

[musiclover]

All you can really do is rework the back end if the frame and bond in proper dropouts.

Well, I guess there is enough surface area there to just glue the drop outs in with epoxy...

[ghostinthemachine]

You'd need to remove paint, prep the surface and provide some sort of wrap to support the join.
Just gluing a block of aluminium to a carbon structure won't last.

[Karvalo]

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