Pictures of my sons BB8 car!

[Crash Enburn]

You want all the running surfaces to be smooth. Your wheels should be running on their edges...

 

[derbydentist]

You want all the running surfaces to be smooth. Your wheels should be running on their edges...

Good point haha

 

[Richard C. Moeur]

The car was indeed fast.

I agree with Crash Enburn's axle method - thin strips of progressively-finer wet sandpaper, then polish - after carefully filing off the flashing and burrs. We use a drill press set on low speed for this work.