Re: I fixed a broken spoke!

12-30-2006, 11:11 AM

On Tue, 19 Dec 2006 08:18:44 -0600, Gary Young <[Only registered and activated users can see links. ]>
wrote:

>On Wed, 06 Dec 2006 21:09:48 -0800, jim beam wrote:
>
>> dvt wrote:
>>> jim beam wrote:
>>>> dvt wrote:
>>>>> jim beam wrote:
>>>>>> but given that the hub flanges are canted and that the angle which
>>>>>> the spoke manufacturer already provides is already appropriate,
>>>>>> there's no point in this exercise in the first place.
>>>
>>>>> You never answered this question the first time, so let's try again...
>>>
>>>> dave, some threads get too long and windy. if you want to /ensure/ i
>>>> read a question that's somehow important, post a new thread. and make
>>>> sure i'm not on vacation, traveling, otherwise busy or disinterested.
>>>
>>> Nice try, jim. Here's the record:
>>>
>>> <http://groups.google.com/group/rec.bicycles.tech/browse_frm/thread/1c072f5d8b7c8892/83a78e954c0f932d>
>>
>> is this the 'unanswered' question?
>> "I've been watching this thread, hoping that I wasn't the only one with
>> this question. How do you "cant and drill" a hole in the hub flange so
>> that both inbound *and* outbound spokes are "optimized?" If the hole was
>> so canted, would that mean that the hubs should not be deformed during
>> the build?"
>>
>> if so, i'd have thought the answers obvious. maybe that's why i didn't
>> bother answering.
>>
>>>
>>>
>>> Scroll down to messages 103-110. You responded to that exact subthread,
>>> so I know you were reading it. But you failed to answer the question.
>>>
>>>>> In bound vs. out bound, crossing pattern, and rim size all affect the
>>>>> angle in question. I don't see hubs marketed for each variation, and
>>>>> I don't see holes labeled for inbound and outbound spokes. Do small
>>>>> wheels (think recumbent) usually use the same hubs as diamond frame
>>>>> bikes? If so, do they have a much higher incidence of spoke breakage?
>>>
>>>> if you want to demonstrate something dave, do the math for the spoke
>>>> angle given that a hub hole may be larger diameter than the spoke and
>>>> seated in a flange of given thickness. then compare that to the stock
>>>> spoke angle of ~95°.
>>>
>>> You made the claim. It's your job to prove it. Here's the claim you
>>> made, in case you've forgotten:
>>>
>>> "the spoke elbow comes pre-formed with the best resultant angle and the
>>> hub flange is canted and drilled also to give the best resultant angle."
>>>
>>> You made no reservations about wheel size, lacing pattern, or any of the
>>> other things you tried to add in later when questioned. And what about
>>> dished wheels? Or rims with offset spoke beds?
>>>
>>> I'm looking forward to your response.
>>>
>> unless you want a full custom hub, the economics don't support
>> accommodating non-standard configurations.
>>
>> two hub pics for consideration:
>> [Only registered and activated users can see links. ]
>> [Only registered and activated users can see links. ]
>>
>> for the cynics, i didn't happen to have any 2.4mm rod about for the hub
>> hole pic, but if you don't believe the hub holes are perpendicular to
>> the flange, do this experiment yourself.
>
>On my XT rear hub, the outer faces of the flanges are canted, but the
>inner faces are perpendicular to the hub axle or very nearly so. (The same
>may be true of my LX front hub, but I'm much less sure; on the rear
>hub, the difference in canting between the inner and outer faces is
>unmistakable even when eyeballing it.)
>
>I can't find a picture of an XT hub that shows this, but if you go to the
>end of this pdf where there are a series of drawings of hubs, they all
>appear to have one canted face and one perpendicular face:
>
>[Only registered and activated users can see links. ]
>
>If the spoke holes were drilled perpendicular to the canted outer face, I
>would expect them to exit the 90-degree inner face at a point further from
>the edge of the flange. But both the outer and inner exit points appear to
>be the same distance from the edge. That leads me to believe that the
>holes are drilled parallel to the hub axle, contrary to the caption on the
>second photo you link to above.
>
>There may be a difference in the way the holes are beveled (if that's the
>right term) on the inside versus the outside, but not that I can see.
>
>The effect of the difference in canting is that the inbound spokes exit at
>what appears to be an optimized angle when their heads are seated squarely
>in the canted outer face (that is, when the heads lie flat against the
>face, with no lifting of any part of the circumference).
>
>However, when the outbound spokes are seated squarely against the
>90-degree inner face, they exit perpendicular to the hub axle, or nearly
>so.
>
>I'm not sure why the hub is designed that way. Is there a reason inbound
>spokes need to have their seating optimized more than outbound spokes?
>Maybe because the elbow angle tends to open up as they are pulled, whereas
>the angle of outbound spokes becomes more acute?
>
>In any event, this does seem to fly in the face of your argument that the
>spoke/hub combination results in an optimized spoke line.
>
>
>
>>
>> for dave, no, there's nothing sinister about this hub being black or
>> large flange. it just happened to be a virgin hub at the top of my
>> parts box.

Dear Jim,

Here's a link to an archery physics page that others may be able to
untangle and apply to bicycle wheels:

[Only registered and activated users can see links. ]

Of course, things are complicated by the springiness of a round-curve
pre-tensioned bicycle wheel versus the much straighter curve of the
pre-tensioned bow, the different angles of a pair of spokes versus a
bow-string, and the spoke crossing that's missing from a bow.

But it looks like something to do with storing energy in a complicated
springy structure. When the rim deforms sideways, it's bending like a
bow. When the squeezed spoke bends the unsqueezed spoke at the
crossing, it's doing the same thing in another plane.

The result, for those like me who get lost in the calculations on the
archery page, is that it's useless to try to calculate spoke tension
increases according to absolute spoke deflection between the two
springy points of the hub and the rim. A bicycle wheel is worthless as
a makeshift tension gauge.

You have to use a tension gauge, which isolates a short, straight span
of spoke with two massively braced posts that reduce this unexpected
behavior, much like a pipe-clamp, to very low levels. The tension
gauge gives either a reading, either Park-style spring-needle mark or
DT-style measured absolute deflection. Then you look up what the
reading means in a calibration/conversion table for a spoke of that
material, shape, and thickness.

So far, no wheel measured with a tension gauge has shown more than
about 55~65 pounds of tension increase for a 60-pound squeeze force.

A spoke in a much more rigid pipe-clamp does a little better, with the
tension increase measured at about ~90 pounds for a 60-lb squeeze
force.

At low squeeze forces created by adding 5-pound weights, the Park
gauge repeatedly shows that the spoke tension in a bicycle wheel drops
at first and returns to its original level only after the spoke has
bent under 20 pounds of weights. The bicycle wheel acts so much like a
springy archer's bow that the simple Park tool reveals the odd
behavior.

When the same weights are added to the same spoke in the rigid
pipe-clamp rig, the Park gauge shows that the spoke tension rises
(instead of dropping and returning to the original level). The pipe
clamp is so rigid that the Park tool is probably not sensitive enough
to reveal the initial drop in tension as the spoke bends.

These details are worth repeating, since they've developed over many
threads and posts.

Cheers,

Carl Fogel

12-30-2006, 11:21 AM

On Sat, 30 Dec 2006 13:11:27 -0700, [Only registered and activated users can see links. ] wrote:

Dear Gary,

Whoops!

Sorry, I wrote that reply not to your post, but to a post from Jim
Beam post way off somewhere else in this thread.

My reply ended up mistakenly attached to your post, probably because
of my careless clicking.

I tacked a copy onto Jim's post.

Cheers,

Carl Fogel