Very small torsion axles

[Forhire]

Our design this season called for some small torsion axles. It turned out to be a fairly involved project to manufacture them. I figured I'd share the build method in the event anyone else needs something similar. One of the challenges we encountered was the figuring out how to put the rubber rods (quarter inch o-ring stock) into the corner of the square tubes. While we were brain storming how to stuff the rubber into the housing I flippantly suggested freezing the rubber rods with liquid nitrogen. After some further research that is exactly how they make trailer torsion axles. Crazy.

It took some preparation and a lot of trial and error. When we started the whole team turned up for the liquid nitrogen portion. After a few failed attempts we got side tracked freezing apples and carrots along with a few other tricks. Pretty soon it was just a couple students and after a couple more hours we finally figured it out.

Step one: Freeze all the components including the dies. This give you a lot more working time.


Step two: Stretch each o-ring section and place it in the V die and quickly press it. It will then freeze into the deformed triangle shape. Work fast otherwise the o-ring may freeze round preventing it from being deformed properly without cracking. This was a three person job, one to stretch, one to close the die, and one to operate the press. Wood was used to help insulate the aluminum dies.


Step three:
Trim one end off the frozen rods with dikes. Then insert the 4 rods into the housing with the axle. Use the thawed end to hold onto the frozen rod. Without the extra end the heat from your fingers will thaw the rod.


Step four:
Thaw the assembly in warm water. The rubber rods will contract back into their original size and shape.


Step five:
Trim the excess rubber with a razor knife.


The rubber holds the axle in place. The axle has about 30 degrees of travel in each direction. The stiffness is controlled by the durometer of the rubber o-ring material used.