Wheel building

[Mark Pearson]

In article <[email protected]>,
[email protected] says...
>
> I must have built at least half a dozen, but, since that has been
> spread out over 30 years or so, it's like being a novice each time.
> Once I did it wrong, and found the spokes crossing over to obstruct
> the valve hole. I swore a bit, and moved all the spokes round by one
> spoke hole.

I did that once but I just live with it. It's awkward but not not
impossible to get to the valve.

--
Cheers,
the.Mark

 

[Ben C]

On 2007-07-11, Jeremy Parker <[email protected]> wrote:
>
> "Paul Boyd" <[email protected]> wrote
>
> [snip]
>
>> So, has anyone taken the plunge and built a wheel that was a
>> success first time round? Experienced wheel-builders seem to knock
>> them out for a past-time (but unless you're doing it professionally
>> why do you need to keep building wheels?), but I'd like to hear
>> from people who might have just built one or two without any
>> problems
>
[...]
> There is, or at least was, a book, "Sutherland's Handbook for Cycle
> Mechanics" which has tables of spoke lengths needed for different
> makes of hub and rim. The book has got thicker, and more expensive,
> over the years, but I imagine bike shops would have a copy, or some
> equivalent.

There are lots of online calculators (I think Simon Brooke just posted
links to several). The formula itself is not too complicated, it's on
Wikipedia.

[...]
> If you have to dish the wheel, as you will for a back wheel, then the
> spokes on the two sides will be of slightly different lengths, not
> enough to need to buy two kinds of spoke, but enough to get two
> different numbers for your spoke thread counts.

For my rear wheel (9 speed, 700c) there was a difference in 2mm between
the two sides. I think that's quite a lot and I did get 16 spokes each
of the two lengths.

Perhaps it would have been OK anyway, especially as the rim is
box-section so there's quite a way to go before the spokes are sticking
up into the inner tube zone.

[...]
> The reason for de-stressing is that when you screw a nipple onto a
> spoke, screwing the nipple twists the spoke rather, winding the spoke
> up like a spring. If you leave the spoke wound up, it will gradually
> try to unwind itself, thereby unscrewing itself from the spoke
> nipple, and messing up the trueness of the wheel, after some miles of
> riding.

I think that's probably most of what's going on. There's a lot of talk
on RBT about stress-relief however, based on the idea that the spokes
may contain residual stresses either from manufacture or from the slight
extra bend introduced in the elbow during the build, that may accelerate
fatigue as the spokes are used causing them to break. These stresses it
is said can be ironed out of the steel by the momentary overload caused
by leaning on the rim as you describe.

 

[Ian Smith]

On Thu, 12 Jul 2007 16:11:04 -0500, Ben C <[email protected]> wrote:
>
> I think that's probably most of what's going on. There's a lot of talk
> on RBT about stress-relief however, based on the idea that the spokes
> may contain residual stresses either from manufacture or from the slight
> extra bend introduced in the elbow during the build, that may accelerate
> fatigue as the spokes are used causing them to break. These stresses it
> is said can be ironed out of the steel by the momentary overload caused
> by leaning on the rim as you describe.

There's a lot of nonsense on RBT, yes.

Things like static stress accelerating fatigue, elastic loading cases
relieving stresses remaining from a plastic deformation, that sort of
thing.

regards, Ian SMith
--
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[Ben C]

On 2007-07-13, Ian Smith <[email protected]> wrote:
> On Thu, 12 Jul 2007 16:11:04 -0500, Ben C <[email protected]> wrote:
>>
>> I think that's probably most of what's going on. There's a lot of talk
>> on RBT about stress-relief however, based on the idea that the spokes
>> may contain residual stresses either from manufacture or from the slight
>> extra bend introduced in the elbow during the build, that may accelerate
>> fatigue as the spokes are used causing them to break. These stresses it
>> is said can be ironed out of the steel by the momentary overload caused
>> by leaning on the rim as you describe.
>
> There's a lot of nonsense on RBT, yes.

Don't tell them I said this but the real reason they keep breaking
spokes is just that they're overweight.

> Things like static stress accelerating fatigue, elastic loading cases
> relieving stresses remaining from a plastic deformation, that sort of
> thing.

So where were you during the great stress relief flame wars?

If you increase the mean stress in a stress cycle you do accelerate
fatigue. And "mechanical stress relief" is supposed to involve a small
amount of plastic deformation. I buy both of those things, certainly the
first one.

What there's not enough evidence of in my opinion:

1. That residual stress from manufacture is significant in spoke
fatigue.
2. That it's still there after normal spoke tensioning anyway.
3. That spoke-line correction is likely to leave the elbows close to
yield stress.
4. That it's really a significant factor in spoke breakages.

All of these of these things _could_ happen, but there's just no real
evidence for them that I've seen.