With the choice of using motorcycle wheels (for aesthetic purposes) instead of smaller go-kart wheels, manufacturing a suitable wheel hub was a real challenge. I needed to use a go-kart wheel hub as that was pre-manufactured to fit perfectly on my axle. I  then needed to create a 'middle piece' that would connect the wheel hub to the larger wheels. What was needed was a perfect circle with a series of holes for bolts to run through. To make matters worse, these holes needed to align perfectly with holes in the wheels which had to be drilled on a chamfered edge of the wheel. That then had to align with the holes in the bolts from the wheel hub. I had multiple attempts to finally get a working design on the third. Initially, I created a 'contraption' to cut the perfect circle by using a square sheet of metal revolving around a threaded bar so it could slowly be rotated towards a fixed angle cutter. This required multiple manufacturing attempts however due to the limit in thickness of metal I could cut with an angle cutter, the forces exerted on the wheel resulting in this adapter bending under the pressure. I tried again by making a circle that instead of resting on top, would sit within thus spreading the overall pressure. In the end, this started to bend as well, so I used fusion 360 to design the perfect adapters and then sent it off to a manufacturer to CNC out of significantly thicker metal. After this 3rd attempt, it finally worked. The rest of the rear axle was simply a case of wrench's and allen keys to attach the sprocket and brake disc to the axle as they were store bought.
Another issue was the lack of custom spacers for the disc brake, so again using fusion 360 I designed custom spacers which were then 3D printed as they didn't need to be strong just lightweight.