Carl,[email protected] said:On 24 Apr 2007 12:47:48 -0700, Ron Ruff <[email protected]> wrote:
>On Apr 23, 10:28 pm, daveornee <daveornee.2pj...@no-
>mx.forums.cyclingforums.com> wrote:
>> I demonstrated a 5% lateral stiffness difference in changing from 14 g
>> to 14/15 DB spokes in an otherwise identical build. In that particular
>> comparison the lateral deflection difference was .07 mm at a 25 pound
>> lateral deflection load.
>
>I'm interested in more details about this. I've tested a few wheels,
>but not with spoke gauge as the only variable. Also, my rig isn't very
>stiff... but it seems like the spokes should have a greater effect
>than that. In the FE model I made, spoke stiffness mattered more than
>the rim stiffness.
Dear Ron,
Dave may be getting the kind of precision needed to measure 0.07 mm
differences in lateral rim deflection with his 25-lb rig.
But the top of Damon Rinard's table mentions that his values are
"average lateral deflection +/- 0.05mm" for what sounds like the same
~25 lb weight hanging from a rim:
http://www.sheldonbrown.com/rinard/wheel/data.htm
Similarly, Damon Rinard's table for deflection in inches (not mm) for
1/4 turns looser shows deflection changing ~0.004 inches (~0.10 mm)
for the first few 1/4 turns looser:
http://www.sheldonbrown.com/rinard/wheel/index.htm
(Page down to Questions 1. Does stiffness vary with spoke tension?)
That suggests that very small tension changes can affect the very
small deflection.
Weirdly, Rinard's deflection _decreased_ according to the measurements
for the first eight 1/4 turns that the nipples were loosened.
Cheers,
Carl Fogel
You discussion reminds me of part of the challenge I/we had in making precise and repeatable measurments: truly smooth, true, and flat rims that stay smooth, true, and flat to within 0.01 mm (or better). From my days in Metrology and with my uncle's guidance he/we decided that to get what I was trying to do .... and seeing such small changes we really needed 0.001 mm smoothness/flatness/trueness. We also needed repeatability in that range. Challenges like this were at first interesting to my uncle, but his interest diminished when I asked him to machine away the "errors" in wheels that I built.
I suppose that I could have a better discussion with Chalo regarding these and other issues revolving around how to do this practically without loosing significant accuracy, but my uncle didn't have the patience and I didn't have the time to persist or make it into a paying proposition.
David Ornee, Western Springs, IL