Bicycle digital spoke tension meter based on Jobst Brandt design

Note: This thing hasn't been updated in years and it's not going to be.

This is a spoke tension meter which uses a spring to create a deflection in a bicycle spoke and a digital gauge to read the deflection. This deflection corresponds to the tension in the spoke. Knowing the tension allows a wheel builder to build to the recommended maximum tension dictated by the rim, and also allows the spoke tension to be balanced, avoiding excessively tight or excessively loose spokes.

This design is based heavily on the original Jobst Brandt design which dates back to 1975. While there are other spoke tension meters out there, I like the Brandt design as it uses a fairly light spring to not add too much deflection to the spoke, and it measures on the same side as the reference points, so is less affected by spoke geometry.

Huge credit goes to Modellaner for his Tensiometer which got me started on this whole thing. It's been such a fun project and I'm nowhere near done yet. Big thanks also go to Quang Vuong who had the idea long before we did and shared everything he had with us. Thanks also to Modellaner for converting the DXF drawings from Quang Vuong to PDF as my efforts in that weren't going so well. I've included that PDF for reference.

This was designed in Fusion 360. In lieu of including the F3D files, which would be static, you can use this link to view the latest version of the design: https://a360.co/2PcaNK6

Note: If you use the gauge I specify, I suggest removing the ball point at the end of the indicator. This doesn't serve any purpose and might make getting a good reading harder as a ball against the side of a cylinder won't be very stable. Plus, it makes the indicator longer and might not give you enough room to insert a spoke when you open the tool. So, before you install the gauge in the tool body, remove the ball point indicator end. This may take some doing as it was installed quite tight on mine. Just use a pair of pliers and unthread it as you would any right-hand screw. You can leave the end of the indicator shaft as it is without anything threaded into the end, the flat end will work nicely with the side of a spoke.

Note on other gauges: Yes, you can swap in any other gauge that fits, but this design is based on certain key dimensions of the gauge that I listed. Another gauge will likely have a different length for the clamp area, and also have a different overall length. None of these things are standardized on linear indicator gauges, and changing any of them changes the function of the tool, so it probably won't work as well for you.

Note on lack of bearings: The idea of this design was to have as few parts that needed to be purchased as possible. To that end, I decided to use smooth posts instead of sealed bearings as are found in the Brandt drawings and on the FSA tensionmeter. Once I have a calibration rig set up, I plan on testing this design against a design with bearings to see if there is a difference in accuracy. Smooth PLA is pretty low friction to begin with, so I'm not expecting a problem.