I was trying to lay out the paint lines on my 4 gallon round badge tank.
My biggest problem is I am as artistic as a mud puddle. I burned through an entire roll of thin-line tape just trying to get a decent looking panel. BTW, if anyone has a few measures of the 4 gallon round badge from an original tank, I would really appreciate it.
Anyway, I decided that if I mounted the badges and knee grips, I would magically be able to do this.
I was trying to put the screws into the knee grip holes, but they were plugged tight with chrome and crap. So I tapped out the holes, and yes on the last hole the tap snapped off.

So there I was with a brand new, freshly chromed tank with a tap broken off below flush.
Some years ago I bought an auction lot full off odd-ball junk, and in this lot was a bunch of tiny boxes with little bitty carbide dentist burs that were never used. Maybe the stuff came from a dentist who passed on, or who knows where this kind of stuff comes from.
I tried it, and I will be damned if it didnt work. It was incredibly slow, I spent over 6 hours working on that tap. The burs just kind of slowly make dust, there are no actual chips involved. Of course I put many, many layers of tape around the hole to protect may tank in case I slipped.
I had a zero production day, but I am awfully happy to be back to where I started.

Lee