Grant Erwin wrote:

For sure I'd try electrolytic derusting first. 5 gallon bucket, 1/4 cup
washing soda or baking soda, clean water, 1 or 2 steel electrodes (I use
railroad track tie plates with copper wire soft soldered to them) and a
wire to your part. Use a car battery charger and hook your part to the
BLACK (-) wire, and the electrodes to the RED (+) wire and let it run
for 1-3 days, then take it out and scrub it with a stiff brush under hot
water and see how you're doing. Might need to disassemble it at that
point and try again. It works real well. I've got a bucket sizzling
downstairs right now cleaning old pipe threading die heads.

This reminds me of an idea I had ages ago. I wanted to make a metal
sphere for a Van de Graaff generator and electroplate it with copper. I
was going to make it from two propane cylinder bases cut off and welded
together. My welding set has a 75 amp battery charger incorporated into
it, and I wondered if this would be good for electroplating? Anyone ever
tried it? By the way, the Van de Graaff project is "on hold" for the
time being, so I'm just asking out of curiousity.

Chris