Lots of iterations to get it right, but with a little Gorilla glue, these wheels are a great savings over buying wheels. My cost per wheel is less than $4 ... so a set of four mecanum wheels only cost me about $15 v. $400+ for off the shelf wheels.
I used a 4" table saw from Harbor-Freight to cut the 3/16" x 3' (4.7625mm x 914.4mm) steel rods to 75mm lengths. I couldn't find aluminum rods which would be easier to cut and smooth out the ends.
Gluing the two spinner halves onto the center of the 75mm axel rods using Gorilla glue and a small clamp to hold them tight onto the axel. After 24 hours the glue is pretty dry and holds strong. I made twelve spinners for two wheels in green and another twelve spinners for two more wheels in purple. You can see how they shift the spinners from left to right for the two types of mecanum wheels needed to provide full x,y control of a robot platform.
I am still looking for a platform frame material. I'd like to get extruded aluminum, but may end up with house trim or similar from my local hardware store. The platform base will probably be cardboard ... I'm too poor to go buy a sheet of plywood or metal plate. If I can, I'll make the lower platform for the RoboGuts circuit board, batteries, motor controllers, radio receiver etc., then have another platform on top of that to host whatever other project may live atop the platform. My 3D CAD model sketch includes Actobotics rails ... not sure if they're the best solution though. I've never worked with Actobotics parts before.