Some of the parts in a pinball machine need more than just a good cleaning with a rag and cleaning solution.  Metal parts can start to get a dull finish over the years and need a good polishing. This is when the vibrating bowl comes into play.

Vibrating bowls work by adding some form of abrasive media to the bowl.  You then add in your parts and turn it on.  It will vibrate the bowl very rapidly forcing the media to rub up against the parts you put inside.

You can get different results using different types of media.  Some stuff is more abrasive than others. I don’t generally use highly abrasive media, that is for things like rust removal.

I use crushed corncob or walnut shells.  The corncob media will give the parts a nice finish after about 8 hours in the bowl.  If the media is getting old from lots of use it can take 24 hours to get the same results.

You could also get similar results using a buffing wheel and compound.  That requires you to manually move the part and stand in front of the machine for hours. With a vibrating bowl I am free to work on other things while it does the work.