Remove Anything from Metal

By John Todd
Category: Workshop, Machining
Difficulty: Moderate

I love using old machine parts for my projects; often their workmanship surpasses that of anything new, and you can get them cheap or even free. Find a junkyard full of ancient, rusty industrial equipment, and you can build almost anything — or at least be inspired to, which is half the battle!

But many older machine parts, especially cheap ones, have rust, paint, or other coverings that make them ugly and difficult to work with. Over the years, my salvage habit has turned me into something of an expert in amateur metal restoration. I am by no means a metalsmith, but I have collected a library of easy techniques that can enable any moderately equipped hobbyist to turn neglected lumps of metal into shiny, working components.

Rust, the oxidation of iron, takes up far more volume than the metal it grows from, so the parts underneath look surprisingly undamaged after treatment. The same goes for old paint, which protects the surfaces underneath it.

There are 3 basic ways to remove oxidation or paint from metal in a home shop: mechanical, chemical, and electrochemical. (Thermal methods, and exotic techniques like dry ice blasting, molten salt dips, and bacterial siderophores, require specialized equipment.) Here I describe some home methods, and how to construct one of the most effective rust-removal tools of all: an electrolytic conversion tank.

Steps

Step #1: Use mechanical methods.

These work well for smooth surfaces with paint or other coatings, and some light rust. For surfaces with cracks, pits, or fine texture, the only effective mechanical method is abrasive blasting (aka sandblasting). But to get into the cracks, you can also follow other mechanical methods with chemical methods.
Safety first: In the shop, I almost always wear leather gloves. A minor slip with a 12,000rpm wire brush will lead to a discouragingly wasted day at the emergency room.
I wear goggles 100% of the time that I’m working with any type of tool or liquid. It’s easier to just leave them on rather than trying to remember, do I have them/where are they/do I need them for this task?
Some of the chemicals used here have nasty fumes, so don’t use more than you need, and use chemicals outdoors, where there is less risk of fume buildup.
Keep a fire extinguisher handy, in case sparks or other heat sources cause flames. A related hint: Do not grind surfaces that are still wet with flammable cleaning liquid. Learn from my mistakes!
Wear respiratory protection when using mechanical methods.

Conclusion

Hints and Notes

The electrolytic bath is basic (caustic), like lye, so wear goggles and rubber gloves and keep a bucket of water or a hose nearby in case you spill or splash some on yourself.

Alligator clip cables work well for suspending small parts like nuts and bolts from the hook.

Painted rusty objects can take much longer because paint impedes electricity. For better results, scratch up the paint first, or use a paint remover before treatment.

Ordinarily, you can dispose of the used bath liquid down the drain. But if you removed lead paint or you suspect that heavy metals (chrome in particular) have leached from your items, let the water evaporate to form a sludge (not a dust!) and bring it to a local toxic materials processor.

Resources

Metals Handbook, Volume 5: Surface Cleaning, Finishing, and Coating, American Society for Metals, various editions and years — an excellent general reference