I can hardly describe how wonderful the electric 4.5" disk grinder that Bo loaned me (Thanks, man!) is for taking the rust and corrosion off the underside of the clawfoot tub. It's truly miraculous the difference POWER makes over my original "wire-brush-by-hand" technique. Here's a shot where you can see what we're dealing with: on the right is the untouched rust, and on the left you can see what a difference just 10 minutes with the grinder makes. (This would have taken AT LEAST 2 hours with the hand brush - probably more.)
Safety glasses, a dust mask, gloves and earplugs are all essential for this job. The little wires come shooting off the brush pretty frequently, and while they only sting a bit hitting arm or leg skin, they'd really do a number on an eyeball.
Cary took a turn with the grinder as well. In just an hour or so we were able to do about 1/3 of the tub! We'll have to figure out something else for the area under the curved rail of the tub though, because the grinder doesn't really fit. I'm planning to swing by Hardware sales this evening to look for some other shape of brush attachment, because I desperately don't want to resort to the wire brush again. I guess once you've tasted power you just can't go back!