RE: [CR]Track ENDS/Nutted Fasteners

(Example: Books)

In-Reply-To: <BMEMJFNOMJHPIMCCGHHOEEBKCEAA.ojv@earthlink.net>
References:
Date: Fri, 29 Mar 2002 10:58:57 -0500
To: "Don Ferris" <ojv@earthlink.net>, <classicrendezvous@bikelist.org>
From: "Sheldon Brown" <CaptBike@sheldonbrown.com>
Subject: RE: [CR]Track ENDS/Nutted Fasteners


Don Ferris wrote:
> As far as the strength
>of a bolted connection, as with anything else, the strength of the assembly
>is only as great as its weakest link. If the case of nuts and bolts, the
>strength of the nut's threads in shear could/would/should equal or exceed
>the the tensile strength of the bolt/axle. Whether or not this is the case
>in all nuts and axles as it applies to all nutted hubs, I can't comment,
>I've never tried to tighten one to failure. You can make the case that not
>all hub nuts are properly designed, but the same is true for skewers. A
>wash. Obviously an axle that has flats on it, ala Sturmey's, etc., the
>threads in the nuts have a reduced area to purchase and would be far weaker
>unless the nut was threaded deeply.

There are a couple of differences you're overlooking. The threads in a QR skewer are adjusted under no load, so there are no frictional heating issues weakening the threads. A thread can _hold_ a greater stress than it can generate by being tightened without damage.

A previous posting seemed to be trying to make the case that a nutted system could clamp more than 4 times as hard as a QR:
>>"that gives a potential of yield strength on a standard steel
>>skewer of around 1,610-pounds based on the root dimension of the
>>threads (4.2mm nom.)...If we assume the same properties for a 4130
>>track axle and nut of standard dimensions, 10mm, then the potential
>>clamping pressure is limited by the root dimension of the axle
>>threads (8.8mm) and its ability to resist tightening stresses,
>>preload, and external load. That'd be about 7,000-pounds...

This skips over the issue of thread engagement. Typical axle nuts are not tall enough to provide sufficient thread engagement to break an axle by overtightening. Instead, the threads will strip. This is not the case with a skewer.

To summarize, indeed, one needs to look at the "weak link".

In the case of a skewer, the skewer shaft is, as noted the weakest link.

In the case of a nutted axle, however, the _threads_ are the weakest link, not the axle shaft, so the comparison quoted above is not relevant, since it ignores this fact.
>>...and since each nut clamps each dropout between itself and the
>>face of the axle, that's 7,000-pounds per dropout.

Huh?

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