For my crossover linkage, I needed to create a rotating shaft with splined ends. This is not as easy as it seems, because cutting splines is obviously beyond my abilities. I’d purchased a Yamaha YZF600R shift shaft, so I had a proper splined shaft to fit my shift pedal linkage, but it was neither the proper diameter nor the right length for the crossover shaft. Simply cutting off the splined end to the end of the shaft and bolting it to the end of my 10mm shaft would not provide a positive coupling, allowing the end to rotate on the shaft and thus negating the whole point of the splines.

As for welding it, I do have both a MIG and TIG welder, but 1) I truly suck using either, 2) once you weld two parts together, it’s pretty hard to re-think/revise/temporarily disassemble. Since I’ve had to come up with at least two iterations of most of the fabricated parts on this bike, bolting things together whenever possible is the more attractive and flexible option.

Finally, after some extended mental gymnastics, I came up with this arrangement:

The idea is that center of the splined end is threaded, not just drilled. The 6mm stud is firmly seated in the shaft, and the splined end is threaded onto the stud. In this way, the splined section can only rotate on the shaft by crawling up the threads, backing away from the end of the shaft. This is prevented by the lock nut, effectively locking everything together. A bit of red Loctite can be added for extra assurance.

I bought some M6 threaded rod, firmly bottomed it out in the shaft’s threaded end hole, and cut it to length. I then hacked off the splined section from the Yamaha shaft. On the lathe, I bored it, tapped it to match, and faced the end square.

I then bolted everything up to see how it went together.

I actually had the shaft bearing mounted inboard of the frame at first, but only way to keep the linkage rod from fouling the pedal was to flip the forward rod end, so the spherical bearing sits inboard of the pivot clamp. I initially made a spacer sleeve for the shaft, but then realized I could simply switch the shaft bearing to the outside of the alloy mounting bracket. At that point, it all went together properly, if not elegantly.

The result is somewhere between clunky and hideous. But “Bultakenstein” isn’t just a clever name. Like Dr. Frankenstein, I am willing to pursue whatever path will result in a functional whole from random dead parts…even if it’s grotesque.

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