that sells complete kits for home plating. They go from simple, cheap kits for small parts, all the way to your basement lab for professional plating. (You can also check the Caswell site for a very handy, downloadable instruction booklet on buffing wheels and compounds.)
Since with typewriters, we usually deal with small parts (and because I didn't want to spend a fortune on an experiment) I invested a full 23 dollars in a small copper and nickel plating brush set, consisting of two bottles of nickel sulphate solution and copper sulphate solution, plus matching electrodes and brushes. (You could also look for nickel sulphate and copper sulphate powder and produce your own solutions and electrodes. That's even cheaper, IF you have access to the chemicals.)
Next, what you need is some hydrochloric acid solution for the final cleanup of your polished piece, some de-mineralized water to rinse it, and an adjustable 3 to 9 Volts power source for the actual plating. You can use a dry cell battery, a battery charger (connect the electrodes to the poles that normally touch the batteries) or get yourself a regular AC/DC converter and DC power supply like the one in the picture. (Don't forget to wear gloves and protective glasses and to work outside or in a well ventilated room. You're fooling around with some nasty materials!)
Before you attack your first typewriter part, it's a good idea to invest a quarter in a cheap steel tea spoon. You'll have something that is well polished to practice on and you'll see that the result can be astonishing. Keep this piece at hand when you start working on old parts. If they don't shine like your spoon, you didn't polish it enough.
First copper, then nickel
The Caswell instruction claim that the nickel plating will work on steel. Forget it. It may work, but not very well. The best way to go is to first put a copper plating on the part and then add the nickel plating.