SAE is about learning so I wanted to share an experience I recently had.
In order to transmit torque from the hub to the wheel, we are using drive pins. Drive pins are simply a cylinder that is press fit into holes on the hub. When the wheel is bolted onto the hub, the pins slide into the holes on the wheel and help transmit torque.
See picture below.
In order for a press fit to work correctly, the two mating parts must be precisely the correct diameter to allow a few thousands of an inch of overlapping material (this is called interference).
Since the pin with be slightly larger than the hole, it must be forced in using a hydraulic press, or cooled down to the point where it has shrunk enough to fit inside the hole.
Rather than pressing our pins in, we decided to cool them with liquid nitrogen, place them in the hole, and allow them to expand in room temperature. Once fully expanded they will be literally stuck in the hole.
The next step was to determine “how much” the pin would shrink when it was dipped into the liquid nitrogen.
Attached is the computer program (PDF) I wrote to help crunch the numbers. It was a very rewarding process!