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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
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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
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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
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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
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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
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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
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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
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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
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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
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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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