Wheel spoking and truing.

[tonyfoale]

A recent post about truing bicycle wheels
Truing a bicycle wheel - GIF
reminded me of a spoking and truing setup that I made and use.

I was told by wheel building professionals that no fixtures could replace the need for manual wheel truing after spoking. Not being a skilled a wheel builder I needed all the help that i could get and I was sure that using physics and an appropriate fixture and spoking technique could replace the skilled manual truing.
Here is a photo description of the tool that I built to sit on a flat optical table.

The most common bearing sizes in the wheels likely to be of interest to me were/are 15, 17 and 20mm, so I decided to use a 15 mm spindle with sleeves to take care of the larger sizes.

Click for full size

The 15mm spindle was a press fit into an old lathe handwheel which gets bolted to the optical table. This gave a rigid and accurate alignment of the wheel centre. After pressing the axle to the handwheel, the axle was mounted in a lathe and the base of the handwheel was machined to ensure truth.

To locate the rim true to the spindle I made three Delrin locating and alignment pieces which were attached to the table via slotted adjustable mounts, so as to cater for 18" and 19" rims.



Adjustable mounts are fine but you need some way to ensure correct alignment, For that purpose I made a setting tool. It pivotted about the 15 mm axle. and a piece at right angles was used to ensure that all three mounts were radially aligned. The far edge of the spindle sleeve was machined flat to sit on a surface plate for setting.



Setting the length of the setting tool.



Using the setting tool to position the rim clamps.



Here are the rim and hub mounted ready for spoking.



That seems to be the limit of the photos that I have, so to continue verbally.
If the wheel was to come off the fixture true, then the spokes had to have near equal tension in all. You can get small torque wrenches for tightening spokes but I know that tightening torque is affected by so many factors that prevent torque being an exact guide to spoke tension. A better guide is its frequency response to an impact. So I set up a microphone to sample the sound when the spoke is given a tap with a small bar. The sound is then passed through a Fourier transform to put the sound into the frequency domain and plot a spectrum. I then tightened the spokes such that fundamental frequency of each spoke had the same amplitude. In general various spokes did not have the same overall spectrum due to numerous factors, but I was confident that equalising the fundamentals was about as good as possible. So it proved, the wheels that I spoke using this technique come off the fixture needing no further alignment. That is the wonder of physics.