Light oil. coarse cloth, such as burlap or canvas. Let oil soak in, wet cloth w oil, rub. Change to clean spot on cloth, rub. Repeat until arm falls off, then change arms. Heavier rust, oil soak, COPPER Chore Boy pot scrubber.
Remember that bluing IS rust (black iron oxide) chemical removers, such as Naval Jelly or hydrochloric acid, will remove bluing.