Add the urethane chemical groups to a metering machine. This machine will heat the chemicals and mix them, creating polyurethane.
Add pigment to the polyurethane when it's in a liquid state. Keep in mind that adding color could make the wheels weak since the dye will take up some space in the wheel, making it less resilient overall. Without pigment, the wheel will be a white color and slightly clear; this type of wheel is considered the most high performance you can get.
Pour the polyurethane into the aluminum wheel molds.
Remove the wheel molds from the aluminum when the polyurethane has hardened. Place the "wheels" on a flat surface.
Use a lathe machine to cut the wheel down to the exact size and shape that you want it. This machine will turn the wheel as it's cutting and remove any extra polyurethane. Make sure that each wheel matches each other, so that all of the skateboard wheels are even.