Whether you found your Underwood typewriter in a hidden corner of your attic or at an antique store, it's probably decades old and due for a thorough cleaning. Rust is particularly stubborn. Besides being unattractive, it can interfere with a typewriter's functioning by causing keys to stick and making your beloved machine impossible to use. Fortunately, you can banish rust from your typewriter with a few key products and some determined cleaning actions.
Buy aluminium polish from an auto supply store and rub it into your Underwood typewriter with a cloth. Be gentle on the fragile sections of the typewriter; you don't want to bend any keys.
Rub away the rust with superfine sandpaper using gentle motions. If sandpaper doesn't work, try superfine steel wool instead, as philosophy professor and typewriter collector Richard Polt from Xavier University recommends on "The Classic Typewriter Page".
Try an electric eraser, or "architect's eraser," to get rid of minor rust. Its spinning tip brushes away rust -- and you can use it for other projects later. Polt recommends the grey ink erasers for tougher jobs.
Scrape away the most stubborn bits of rust with a miniature power drill. Wear safety glasses and drill very slowly, with a gentle touch.
Try a chemical rust-remover product -- available from some home supply stores -- if you know how to take your typewriter apart and don't mind damaging the paint job. Immerse the rusty parts of the typewriter in a bowl of the rust-remover for 30 minutes. The rust should vanish.
Wipe down rusty parts with an oil-moistened cloth, as R. M. Kasten suggests in his Popular Science article "First Aid for Typewriters," from 1941. This will help prevent rust build-up in the future.