Bicycle digital spoke tension meter based on Jobst Brandt design

A bicycle spoke tension meter based on the original Jobst Brandt design, my personal favorite. Once calibrated, the tension meter is less affected by spoke geometry than others because the deflection is measured from the same side as the fixed points, unlike most others which measure across the spoke.

Read this! This original design dates back to 2018. I have done very little with it since then, and a bunch of the info in here is going to be a bit dated. Links have likely changed and might not work anymore.

Also read this! The description is long but this is the most important part. The original design specified a spring which can be hard to source, but if you swap in whatever spring you've got on hand, the odds are good it will be far too strong and cause not only too much deflection in the spoke (affecting the spoke's tension) it will likely cause this design to flex. If this happens, it's not the fault of the design, but the fault of swapping in a spring that is far too heavy. When configured with the right spring, the deflection of the spoke should be under a millimeter which keeps it from changing the tension in the spoke. Jobst Brandt knew what he was doing when he designed this, and if you can't be bothered to source the right spring, any shortcomings in your results are your decision.

Note: I've made this and tested it against my FSA and it matched the trends very closely, but it can only give relative readings, which would be useful for tension balancing. Without calibration it can't give useful info as to the actual spoke tension. A calibration rig could solve this problem, and I've got the parts to make one, but have not yet built it because I just use my already calibrated FSA.

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, even if I haven't touched this in years. 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.

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 tension meter. I don't expect that this will make a notable difference in the reading, but if I ever set up a calibration rig, I'll be able to test.

Note on the spring: Jobst Brandt specified a spring in his original design, (Lee LC-032E-15) and that spring is pretty tough to source, but I managed it. Other folks who have printed this have ignored that and swapped in any old spring they had on hand which fit, and those were often too firm and caused issues, which they attributed to shortcomings in my design. If you use the proper specified spring, it works as designed. If you don't, that's on you, not the design.

Print Settings

All the stuff below is how I printed it back in the day. How I would print it now is pretty straightforward. I would likely do 0.2mm layer height with a 0.4mm nozzle, at least four shells, and maybe up the top and bottom layers a couple. At least 20% infill, grid or cubic -- gyroid if you wanna be fancy. (* don't believe the youtubers who $#!+ on grid infill - if you have a good slicer and a good printer it is a perfectly cromulent infill pattern) These basic settings would very likely be more than sufficient for all of the. parts. The one possible exception is the 0.05mm layer height on the spring seat since I was trying to get good results on the M8x0.5 thread which is ridiculously fine. No doubt by now if you can still get this gauge, the thread may have changed, so that might not be necessary.

Notes:

This is archaic, and how I originally sliced it back in 2018, I'm only leaving it here for historical reference.

I used different settings for the different parts. All were sliced in PrusaSlicer

• Main body - 0.15mm layer height, 20% infill, two shells

• Handle - 0.15mm layer height, 20% infill, two shells

• Gauge clamp - 0.15mm layer height, 70% infill, two shells

• Bar with anvil - 0.15mm layer height, 50% infill, two shells

Spring seat - 0.05mm layer height, 50% infill, two shells
The 0.05mm layer height on the spring seat wasn't absolutely necessary, I was just trying to get better results on the fine M8x0.5mm thread. Considering the M3 threads printed into the main body and handle are the same 0.5mm pitch and printed just fine at the higher 0.15mm layer height, I don't see why this wouldn't work for the spring seat - I just haven't tried it yet.

I've also carefully designed all the parts so that they don't need any supports when printed as-is. You may choose to add them, but if your printer is pretty well calibrated and you use the settings I list above, you should be able to print with no supports and still get really good results.

I also have had a Monoprice Select Mini printer with a 120mm build volume - and I have managed to keep all of the partsjust inside that volume. The bar with anvil needs to be rotated 45 degrees, and you'll have to turn off any skirt, brim, or raft, but itjust fits. If you are still running a Monoprice Mini, goddamn -- bravo.

Design details

Design history

Original design: Jobst Brandt, 5 November 1975 (wow!)
First 3D printed version: Quang Vuong
Another 3D printed version: Modellaner

3D printed version of the DT Swiss tension meter by WheresWaldo

Original comment thread on the Modellaner design.
Follow-up discussion on the Bike group

Required hardware

I designed this to need as few non-printable parts as possible. I've got the list down to only three different types of parts:

1. 12.7mm digital indicator
   I found this version from Clockwise Tools on Amazon but this looks to be a generally available gauge from many vendors.
   
   I should also mention that after using the digital gauge version, I actually prefer using the dial gauge version that I have on my FSA tensionmeter. It's a personal thing but I feel like I get a better idea of the deflection by seeing the needle move.
    

2. M3x16mm screws
   A total of 8 are needed, but a pack of them is cheap enough. Alternatively, you can find these at most hardware stores. You may wish to add M3 washers, but it's not absolutely necessary.
    

3. A Lee LC-032E-15 spring
   which has the following specifications:

   • 0.36" OD

   • 0.032" wire diameter (music wire, not stainless)

   • 2" free length

   • 4 lbs/in spring rate
     I found [this one on Amazon](http://a.co/d/3mUUVHh) but it's currently unavailable.