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I want to calibrate my Park Tool TM-1 for my weird spokes. I want to build a box with some kind of weight mesuring device where a spoke can be put under 1600N of tension.

Rummers on other boards say that using a spring scale would yield wrong results, because the spring would move while messuring. I don't quite know if that is true or not?

Because I want a cheap solution, I don't want to spend 50 euros on a digital scale. Now I found a "butcher's scale" on ebay here. Can I use that for my purpose, or will it also yield wrong tensiometer reults? I don't really understand the rational behind a spring scale messing up the results. Can someone shed some light on this?

Edit: Here is a picture and the discussion from some other board: enter link description here

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Hang the spoke (from something very strong) and apply 1600N of weight (359.7 pounds/163Kg). –  Daniel R Hicks Aug 24 '12 at 13:41
    
That was my first idea, but I can't think of any place to mount the spoke, and I can't think of anything that weighs 160kg and is mountable to a spoke... :-( –  Franz Kafka Aug 24 '12 at 13:49
    
Have you contacted Park Tool to see if they have the conversion table you need. If your spokes are unusual they may not have published the results –  mikes Aug 24 '12 at 17:10
    
Did so now. See if they still answer today. But I still want to build this tool, just for the sake of it. –  Franz Kafka Aug 24 '12 at 18:14
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Well, you of course need brackets of some sort to grip the spoke ends. One end would be a metal plate with a hole drilled the same size as a hub flange hole. The other end would be a metal plate with a hole to accept a nipple, the plate bent in an L or U shape. Hang it from a joist in your garage/basement/wherever. (A swing set at a park would work.) As for the weight, you're on your own. (But there's no reason why a spring balance wouldn't work as well, if it's accurate enough for you.) –  Daniel R Hicks Aug 25 '12 at 12:11
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1 Answer 1

I'm not sure what you're after here. Is your spoke type not available on Park's TM-1 Tension Meter Conversion Table? You're after relative spoke tension when you're measuring your tension as it's going to be different at different points from the hub to the rim. 1600N is well within the range of measurement for the TM-1 on almost all spoke types

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Thanks, yes my spoke type is not listen. The aero spokes are only 1mm thick. Park Tool has only listen aero spokes starting from 1,5mm thickness. I want to know if I can use the scale from the link, or if that will somehow give my wrong results. Furthermore I would like to know why the results from spring based scales in combination with tensionmeters would give me a wrong result. –  Franz Kafka Aug 24 '12 at 14:20
    
A spring based scale will be affected by the weight and/or tension added/subtracted by the tool itself. You need some method of applying a fixed amount of tension like a static weight or known force that is connected to a fixed object like a bench. Since a scale is variable when you apply the tension meter you'll not only be measuring the spoke's tension, you'll be measuring partial force applied and measured by the springs in the scale. –  Tha Riddla Aug 24 '12 at 14:31
    
Yeah that makes sense, but the added tension to my spoke through the measuring tool should be neglectable compared to initial tension of 1600N. I don't think the bending of the spoke will have an great impact. I want to build something like discussed on the other board. Please click the link in my edited inital post (right at the bottom) and just quickly scroll through the thread to see the pictures. Then we might have the same understanding of what I want to do :-) –  Franz Kafka Aug 24 '12 at 14:39
    
Yes, the goal is understood. The rig that has the digital meter is what you need to account for. There seems to be some way of measuring the tension with a scale and then locking it off, which takes any force yielded by the scale out of the equation for accurate calibration. What you're after is calibrating a measurement tool (TM-1) to a fixed standard. Having an additional variable (a scale) contained in the setup will yield an inaccurate calibration, which defeats the purpose of the measurement rig you are building. Does that make sense? –  Tha Riddla Aug 24 '12 at 14:55
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Evey (non-exotic) scale made is either a spring scale or a balance scale. Virtually all digital scales are spring scales. It's just a question of how far the spring moves for a given weight. In a way the simple (non-digital) spring scale is apt to be MORE accurate, since the applied force will increase less with a slight change in spoke length (due to the sideways deflection). But in any event the change in spoke length is going to be negligible, relative to the accuracy of the gauge. –  Daniel R Hicks Aug 25 '12 at 12:18
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