Unicycle

This is a project I worked on last semester and finished sometime around April 2010. I can’t actually ride a unicycle yet, but at least now I have one to practice with. I machined the fork structure, hub, and cranks.

homemade unicycle

The two round plates holding the spokes were cut from sheet metal and are screwed into the center cylinder. This cylinder along with both cranks are fixed to a half inch stainless steel axle ( no particular reason for stainless steel, I just happen to have it lying around). The two hex bolts in the center of the hub served as the set screws to the central axle. If I were to do this again, I would definitely pick another way of securing everything to this axle. There is simply too much torque involved. At this point, I have tightened the set screws down so much that the end of their threads are slightly mangled, so I would damage the threads in the hub if I ever took the screws out.

unicycle hub and cranks

The cranks are keyed and clamped to the axle. The key does not extend the full width of the crank, so it is not visible from the sides. Overall, this has been a very effective method in securing the cranks. For added aesthetics I machined some grooves with a ball-end mill. The corners were also rounded on a sander.

closeup of crank arm

The bearings are held in a block of metal between the crank and the hub. The bearing is barely pressed in, which is fine because there is not much force trying to push it out. To make it I started with a rectangular chunk, then turned the necessary features on a 4-jaw chuck.

crank attachment, bearing block, and hub

The brackets that hold the frame tubes together were cut out on a water jet. The holes that hold the tube were then bored out, and the middle was slit with a slitting saw. There used to be posts sticking out on the rounded edges that made it easy to clamp and locate the part, but those were sanded off in the finishing process. Overall, this is an effective way of holding the tubes without welding.

brackets that hold the tubes together

The seatpost is a 1/8 inch piece of sheet metal attached to a tube using that aluminum solder stuff from McMaster. I even machined a step for the tube to sit in. But I think the surfaces weren’t clean enough, and so this joint eventually failed. Hopefully the next version will be welded together. ‘I need to learn to weld aluminum’ is becoming quite a recurring theme in my projects.

aluminum soldered seat post

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