I broke off the tip of a 0.038" uncoated HSS drill bit in the 1/32" orifice of a solenoid valve and decided to test the recommendation made several times on rec.crafts.metalworking that alum would dissolve steel from aluminum. This was in stainless steel but I figured that was sufficiently less reactive than steel that it might work. I added about
1.5 teaspoons of McCormick brand "Alum" from the spice isle at a local grocery store (WEIS, Laurel, MD) to about 4 tablespoons of hot water (between 160 and 200 F). Almost all dissolved. I rinsed the valve body in hot tap water to preheat it, then put it in a small plastic bowl and poured the alum solution in until the orifice was covered and liquid was present in both elbows (see the picture). After a few minutes a small black film was visible around the orifice. I put the bowl in a ziploc bag and put that in an oven at 150 F overnight. In the morning the inside of the valve body was covered with a black film and the drill bit tip was complete gone. I removed the film by soaking in a strong warm trisodium phosphate solution for several minutes, with rubbing with my fingertip. Overall a complete success. I whipped up my very first web site so if you want to see a picture of the valve body go to
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Oh, at a guess the piece of drill bit was 0.03 to 0.05" long so the total amount of steel dissolved wasn't great, but since it was down at the bottom of a hole the access was pretty bad too.
-- Regards, Carl Ijames carl.ijames at verizon.net