How about a welder for edm power source?

Unfortunately nowhere near. I tried the welder. Made a cylindrical back cap out of delrin and brass, chucked in the drill press with the test piece well insulated and the chuck grounded to the column. It didn't do much. I tried ac, dc, varied frequency, pulser, etc. Interesting, but I'm not going to live long enough to get anything useful done.

Oh, tried welding the tap too. finally got some ss welded on the tiny tap, but it broke off deep in the hole when I tried it. Then even with a sharp .040" tungsten, the arc just raced around the cast iron in a little circle.

By the way, +2.5 diopter cheaters in the hood plus my 18" focal length safety glasses gave me a good close view of the arc and work area.

Looks like Ed was right. Langlois' book talks about switching in capacitors for more spark, up to 700 microfarads. So I'm going to start that way, putting together a list of stuff the surplus place in town has available.

--Did you submerge the operation in a dielectric like mineral oil? It doesn't really work unless the arc is constrained by some sort of goo.

I didn't, based on Huntress' suggestion that the tap burners he used were run in air. Might try that sometime, but found a commercial edm shop nearby with a $75 hourly rate that said they could do it in under an hour, so we'll see. Definitely cheaper than all those caps, transformers, etc., even surplus.

I am going to invest in a hand tapping machine, though. Well worth it.

Pete Keillor

Yeah, the basic tap busters were just run in air. An oil dielectric allows the electrode to get closer for more precise sparking, but it requires a really good touch (or a decent servo mechanism) to keep the spark distance in the right range.

Sometimes you can get a used one cheap, I think it's more trouble and expense to make your own than it's worth.

'Too bad the welder didn't work. I had a feeling that it would be difficult, but it was worth a try.