25 Sep Spoke tension meter calibration tool
Recently I bought two Park Tool tension meters more. I had got a Park Tool and a SuperB tension meter at this time. I checked the calibration of all 4 tension meters. The result was shocking. The SuperB and the Park Tool tension meters showed the same result. But the others were different. So I decided to build a calibration tool for these which I had intended for a long time.
The concept of this tool is simple. The unit for tension measurement is kgf (kilogram-force). If a 10kg barbel is hung at the end of a spoke and the other end is hung on a spoke hole of a hub flange, this is 10 kgf tension on the spoke.
Usually, 100 kgf is standard tension on a spoke in a wheel. So using a digital weight gauge, a spoke and some aluminum structures build a calibration tool. A Sapim 2mm round spoke is hooked at the one end of the gauge, And the other end of the gauge, a hook bolt is attached.
The threaded spoke end goes through a hole in a support then fasten a nipple at the outside of the support. For the hook, make a hole with little bit larger diameter than the hook in the opposite side support. The hook also goes through this hole and attach the bolt.
It’s ready. Turn on the gauge then set zero first. After that slowly fasten the bolt until the gauge shows 70kg.
For 2mm round spokes, 70kgf is 17 deflection reading on the TM-1 Park Tool tension meter. If the measurement of the tension on the spoke in the calibration tool is 17, calibration of the tension meter is good. My two TM-1 showed the wrong value.
For tuning calibration, flipped back TM-1 and released the spring then turned the bolt. Replaced back the spring and measured the spoke again. Until it showed 17, adjusted the bolt a few times.
Finally done all the calibration.