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Spoke Tension Calibration Curves



 
 
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  #1  
Old October 15th 06, 11:49 PM posted to rec.bicycles.tech
Andy Froncioni
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Posts: 27
Default Spoke Tension Calibration Curves

I recently bought a fancy DT-Swiss Tensio tensiometer. Yup, the
expensive kind.

Ok, so now I have this nice tool that only comes with calibration
curves for ... wait for it... only DT-Swiss spokes. My wheels are
bladed Shimano WH-R550's, so all the provided curves are useless.

Unless anyone has created their own calibration curves, I'm going to
attempt to do it myself. I'll make a jig and start measuring the
deflection on the dial gauge with known weights on the spoke. I guess
it's that simple.

Questions:

1) Has anyone ever tried this themselves?
2) Is anyone interested in my results? If so, I'll post them.
3) Does anyone need any calibrations? Send me the spokes and I'll do
the calibration curves, once I'm set up.

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  #2  
Old October 16th 06, 02:35 AM posted to rec.bicycles.tech
Leo Lichtman
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Posts: 767
Default Spoke Tension Calibration Curves


"Andy Froncioni" wrote: (clip) I'll make a jig and start measuring the
deflection on the dial gauge with known weights on the spoke. I guess it's
that simple. (clip)
^^^^^^^^^^^^^^^^
If this is too obvious, forgive me: Align the tensiometer across the thin
dimension of the spoke--that will give you the greatest sensitivity, and
will be the easiest position to achieve consistently. If it is hard to tell
physically when the alignment is perfect, it will be the position which
gives the maximum reading on the tensiometer.


  #3  
Old October 16th 06, 02:45 AM posted to rec.bicycles.tech
Andy Froncioni
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Posts: 27
Default Spoke Tension Calibration Curves


Leo Lichtman wrote:
Align the tensiometer across the thin
dimension of the spoke--that will give you the greatest sensitivity, and
will be the easiest position to achieve consistently. If it is hard to tell
physically when the alignment is perfect, it will be the position which
gives the maximum reading on the tensiometer.


Yes, I've noticed it's the most "stable" position. But there's still
a little play in the
dal gauge readings. I have to jiggle the tensiometer a bit to get the
reading to stabilise
further. I'm assuming that this happens when the tensiometer is
reading the smallest
axis.

  #4  
Old October 16th 06, 05:17 AM posted to rec.bicycles.tech
Joe Riel
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Posts: 129
Default Spoke Tension Calibration Curves

"Andy Froncioni" writes:

I recently bought a fancy DT-Swiss Tensio tensiometer. Yup, the
expensive kind.

Ok, so now I have this nice tool that only comes with calibration
curves for ... wait for it... only DT-Swiss spokes. My wheels are
bladed Shimano WH-R550's, so all the provided curves are useless.

Unless anyone has created their own calibration curves, I'm going to
attempt to do it myself. I'll make a jig and start measuring the
deflection on the dial gauge with known weights on the spoke. I guess
it's that simple.

Questions:

1) Has anyone ever tried this themselves?
2) Is anyone interested in my results? If so, I'll post them.
3) Does anyone need any calibrations? Send me the spokes and I'll do
the calibration curves, once I'm set up.


I'm interested in the results. I'm in the process of finishing up a
theoretical analysis of the performanance of tenisometers and would
like to see how its predictions compare to actual performance.

--
Joe Riel
  #5  
Old October 16th 06, 05:36 AM posted to rec.bicycles.tech
Dan
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Posts: 195
Default Spoke Tension Calibration Curves

Andy Froncioni wrote:
I'll make a jig and start measuring the
deflection on the dial gauge with known weights on the spoke.


Might not work very well since the ends of the spoke won't be held in
position like they would when assembled in a wheel. The wheel keeps the
ends aligned and parallel.

For round spokes, the reading should be about the same for the same
cross-sectional area. The area is proportional to the diameter squared:

From their charts:
http://www.dtswiss.com/data/files/MA...1202133804.pdf
A 1.8 spoke at 1000N is 1.77, 1.77/(1.8^2) = .546
A 2.0 spoke at 1000N is 2.19, 2.19/(2.0^2) = .547
a 2.34 spoke at 1000N is 3.00, 3.00/(2.34^2) = .548

Seems to increase slightly with spoke diameter so the bending stiffness
has something to do with it.

a flat spoke (or smaller diameter spoke) will have a lower bending
stiffness (moment of inertia) and therefore a lower reading. By
calculating cross sectional area and moment of inertia for various
spokes in their table it might be possible to empirically solve for any
spoke moment of inertia, area and tension.

Moment of inertia for a round: I = (pi)(diam^4)/64
For a rectangle: I = (width)(thickness^3)/12

I have not investigated this before so I am interested to hear what
others say.

Dan
  #6  
Old October 16th 06, 06:41 AM posted to rec.bicycles.tech
[email protected]
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Posts: 7,934
Default Spoke Tension Calibration Curves

On Sun, 15 Oct 2006 21:36:22 -0700, Dan
wrote:

Andy Froncioni wrote:
I'll make a jig and start measuring the
deflection on the dial gauge with known weights on the spoke.


Might not work very well since the ends of the spoke won't be held in
position like they would when assembled in a wheel. The wheel keeps the
ends aligned and parallel.

For round spokes, the reading should be about the same for the same
cross-sectional area. The area is proportional to the diameter squared:

From their charts:
http://www.dtswiss.com/data/files/MA...1202133804.pdf
A 1.8 spoke at 1000N is 1.77, 1.77/(1.8^2) = .546
A 2.0 spoke at 1000N is 2.19, 2.19/(2.0^2) = .547
a 2.34 spoke at 1000N is 3.00, 3.00/(2.34^2) = .548

Seems to increase slightly with spoke diameter so the bending stiffness
has something to do with it.

a flat spoke (or smaller diameter spoke) will have a lower bending
stiffness (moment of inertia) and therefore a lower reading. By
calculating cross sectional area and moment of inertia for various
spokes in their table it might be possible to empirically solve for any
spoke moment of inertia, area and tension.

Moment of inertia for a round: I = (pi)(diam^4)/64
For a rectangle: I = (width)(thickness^3)/12

I have not investigated this before so I am interested to hear what
others say.

Dan


Dear Dan,

You can investigate the effect of cross-section on a bicycle spoke
tension gauge by visiting a motorcycle shop.

Here's a picture of a bicycle spoke and a motorcycle spoke:

http://home.comcast.net/~carlfogel/download/spokes.jpg

The bicycle spoke is a typical 2 mm.

The motorcycle spoke is considered flimsy and is single-butted at the
hub end, 4.0 mm x 3.5 mm.

It gives an impressive tension reading when stuck loose in the jaws of
a tension gauge whose post-width and spring-force are designed for
bicycle spokes--the tension gauge's spring will be held back by the
bending resistance of the untensioned motorcycle spoke.

Cheers,

Carl Fogel
  #7  
Old October 16th 06, 01:10 PM posted to rec.bicycles.tech
Andy Froncioni
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Posts: 27
Default Spoke Tension Calibration Curves


Dan wrote:
Andy Froncioni wrote:
I'll make a jig and start measuring the
deflection on the dial gauge with known weights on the spoke.


Might not work very well since the ends of the spoke won't be held in
position like they would when assembled in a wheel. The wheel keeps the
ends aligned and parallel.


I'll pin one end and use the Shimano rim piece to float the other end.
That should
align the forces properly.

I figure if I put 100, 200, 300, ..., 800 N of tension on the spoke and
measure the
Tensio deflection each time, that should give me a pretty good graph.

Easy as this is, I wonder why a tensiometer manufacturer would not
perform these tests
themselves, for goodness sake. There oughta be a website...

Cheers!

Andy

  #8  
Old October 16th 06, 01:31 PM posted to rec.bicycles.tech
Qui si parla Campagnolo Qui si parla Campagnolo is offline
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First recorded activity by CycleBanter: Jul 2006
Posts: 3,259
Default Spoke Tension Calibration Curves


Andy Froncioni wrote:
I recently bought a fancy DT-Swiss Tensio tensiometer. Yup, the
expensive kind.

Ok, so now I have this nice tool that only comes with calibration
curves for ... wait for it... only DT-Swiss spokes. My wheels are
bladed Shimano WH-R550's, so all the provided curves are useless.


Not really. Just measure the thickness of the shimano spoke center
section and use the corrresponding spoke thickness that matches a DT
one, like the new bladed one. Or extrapolate.

Unless anyone has created their own calibration curves, I'm going to
attempt to do it myself. I'll make a jig and start measuring the
deflection on the dial gauge with known weights on the spoke. I guess
it's that simple.

Questions:

1) Has anyone ever tried this themselves?
2) Is anyone interested in my results? If so, I'll post them.
3) Does anyone need any calibrations? Send me the spokes and I'll do
the calibration curves, once I'm set up.


  #9  
Old October 16th 06, 02:30 PM posted to rec.bicycles.tech
Andy Froncioni
external usenet poster
 
Posts: 27
Default Spoke Tension Calibration Curves


Qui si parla Campagnolo wrote:
Andy Froncioni wrote:
I recently bought a fancy DT-Swiss Tensio tensiometer. Yup, the
expensive kind.

Ok, so now I have this nice tool that only comes with calibration
curves for ... wait for it... only DT-Swiss spokes. My wheels are
bladed Shimano WH-R550's, so all the provided curves are useless.


Not really. Just measure the thickness of the shimano spoke center
section and use the corrresponding spoke thickness that matches a DT
one, like the new bladed one. Or extrapolate.


No, you can't do that. The bending moment of a non-circular
cross-section
rod is highly dependent on its shape. A rectangular cross-section vs.
an elliptical
cross-section will yield vastly different bending behaviours.

  #10  
Old October 16th 06, 02:34 PM posted to rec.bicycles.tech
amakyonin
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Posts: 101
Default Spoke Tension Calibration Curves


Andy Froncioni wrote:

Unless anyone has created their own calibration curves, I'm going to
attempt to do it myself. I'll make a jig and start measuring the
deflection on the dial gauge with known weights on the spoke. I guess
it's that simple.


A better way would be to get a copy of the conversion table for the
Park tensiometer. It covers a veiety of spokes. With a litle analysis,
you can then correlate the readings of the DT gauge with the Park gauge
using matching spokes from each table. This will give you a way to
convert from DT units into Park units. You can then reverse the
conversion to get the proper DT reading for the bladed spokes listed on
the Park table.

 




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