I spent a lot of time looking at, and experimenting with, rust removal methods - posted a lot of it in an A.S. thread:
http://www.arboristsite.com/community/threads/philberts-chain-salvage-challenge.245369/
EvapoRust works well on surface rust, in my experience, but not so good on deep, pitted, rust. Keep the solution covered, as is does not work as well if some of the water evaporates, and use it until it does not work anymore (keep it in a separate container from the un-used stuff) to get your money's worth. A similar product is
WD-40 Rust Soak Remover http://wd40specialist.com/products/rust-remover/ There are a few other brand names now - some may be available at a lower cost through different vendors.
Acids work well too, but have their own issues: sulfuric acid and hydrochloric acid (including
muriatic acid) can be nasty to work with, put out hydrogen fumes, and can attack the underlying metal. I don't encourage using them, unless used outside, diluted, and when you have few other choices. Wear gloves and goggles.
'Naval Jelly'
http://www.loctiteproducts.com/p/s_trmt_naval/overview/Loctite-Naval-Jelly-Rust-Dissolver.htm is primarily phosphoric acid, which works well, and is thickened to keep from running off if painted onto a rusty object (instead of dipping). But it attacks chrome and aluminum, so you have to be careful with saw chains, some tools, parts, etc.
I also played around with inorganic acids:
acetic (vinegar),
oxalic, and
citric. Each of these work, and are not as nasty as the organic acids mentioned above, and even available in food grade on Amazon or eBay. They are fairly inexpensive. But each of these can stain the metal black or green, if left in too long. That may or may not be an issue, depending on what you are working on. Root around the Internet for details on each.
One of my favorite methods is
electrolysis, which uses electricity and water, to transfer rust from the item to a sacrificial electrode (old file, graphite, etc.). Again, root around the Internet and look at a few different articles - some explain it better than others, and some offer less elaborate set ups. Follow the safety recommendations. I picked up a few battery chargers at garage sales for $5 or $10 each to use just for this purpose.
And, of course, removing rust does not replace the lost metal!
Philbert