Making an Axle for a Gear Assembly
The side length calculations are in the PDF below.
(When cutting out 110 lb card stock, I discovered that you need to cut the design with two passes.)
Here is the PDF. I used 65 lb card stock for the gears and 110 lb. card stock for the base.
Glue all of the axles into a tube and glue them to the round axle bases.
Glue the corresponding gear pieces together. Make sure that the interior axle shape is exactly the same when sandwiched together. I used different color paper to differentiate the types of axles.
Thread the axle assembly through the base. Bottom of the base shown above.
Thread the corresponding gear onto the axle.
Fold and apply glue as shown above.
Apply more glue as shown.
Bend into the improved axle with internal structure.
The improved axle design is very sturdy. I can think of other internal structures for the other shapes. Maybe you can too. See if you can design an internal structure. I have already many of the calculations for you in the PDF.