Nick Leone wrote:
Looking around, there are several hacked-together EDM based tap removal
techniques on the web. Here are two that I found interesting:

http://www.pico-systems.com/edm.html
This will work, it is extremely slow. If you can use a hollow electrode
it should help immensely by flushing out the crud. You know it is
working when a lot of black crud develops - that's atomized metal.
You need a method to move the electrode up and down in incredibly small
movements. I actually leaned on the head of my Bridgeport as the fine
feed, and used CNC feed at .01 IPM or so as the coarse feed. When you
get it working right, the electrode makes a sizzling sound, but it is
very hard to keep the gap just where that happens.

I have burned out a couple 4-40 taps this way, but it is very slow
going. An electronic pulser for this is on my "to do" list, but I don't
know when I'll get to it.

Jon