Mix a batch of polyurethane. Combine the chemical components of the polyurethane in the appropriate proportions in a metering machine. A metering machine is a machine that heats, mixes and dispenses polyurethane.
Add color. When the polyurethane in the metering machine is a liquid, add dye or some other type of pigment to the batch. This is only necessary if you want your skateboard wheels to have a color.
Pour polyurethane into molds. The molds should be made of aluminum and reflect the shape and size you want your wheels to be.
Remove the polyurethane "slugs" from the mold after the polyurethane has solidified. Slugs are the basic, unfinished form of your polyurethane skateboard wheels. Place the slugs on a flat surface to fully cure.
Shape the wheel. Use a lathe to cut the slug into shape. The sides and riding surface of the wheels should be cut to match each other exactly. A lathe is a piece of machinery that turns an object as it shapes it. In this case the lathe turns the slug as it cuts away excess polyurethane.