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Oh, yes, one other thing mentioned that I did recently --

I had some broken off taps in parts I was making, and decided one
weekend to see what I could do about that. I threw together a low
power EDM system from a large assortment of miscellaneous
parts. I made an electrode from a piece of 1/16" brazing rod
with one end brazed into a socket head cap screw. I threaded
the screw into a big nylon spacer I had, and mounted that in my
milling machine's Jacobs chuck. I was able to use the CNC
mill's positioning system to move the electrode just where I
wanted it. For EDM fluid, I first tried tap water, but that foamed
and sputtered away quickly. I then went to alum-tap tapping
fluid, which worked fantastically as an EDM fluid. I set up
for about 30 V open circuit, and started the mill in the slowest
backgear range (80 RPM). With the brazing rod almost perfectly
straight, it orbited about .010 - .015", clearing out a bigger hole
in the tap than the diameter of the rd, itself.

I programmed the CNC to advance the spindle at about .006
to .01" per minute, and used the feed override to keep EDM
current between .25 and .5 Amp. I replenished the fluid as needed,
and raised the electrode and cleaned out the hole when progress
stopped (about every .020"). I got rid of each tap in about 10
to 25 minutes, depending on how much of the tap was left down
in the hole. Mostly, after the EDM operation, all that was left of
the tap was the very tip of the flutes, and they could be picked
out with a fine needle. All the holes were later tapped and
the parts used. An earlier attempt to burn the taps out with
Nitric Acid was not very successful, and left the aluminum
slightly stained, but the EDM did no damage to the workpiece
at all.

I plan to put all this, including diagrams and photos on my
web pages.

Jon

Looking forward to seeing your web pages on this. I just gor a brochure for a small tap remover from Taiwan but havn't got a
price on it yet. take a look at

I worked in a mold shop that had a Camman tap buster, it used molybdenum tubing for the electrode and a milky colored dialectric
coolant fluid. I had used it to remove everything from a 2-56 tap to stuck 2" shcs.
These things can save a lot of parts and I wouldn't mind making one for myself .
Jon Elson wrote:

From: Jon Elson <jmelson@...>

Oh, yes, one other thing mentioned that I did recently --

I had some broken off taps in parts I was making, and decided one
weekend to see what I could do about that. I threw together a low
power EDM system from a large assortment of miscellaneous
parts. I made an electrode from a piece of 1/16" brazing rod
with one end brazed into a socket head cap screw. I threaded
the screw into a big nylon spacer I had, and mounted that in my
milling machine's Jacobs chuck. I was able to use the CNC
mill's positioning system to move the electrode just where I
wanted it. For EDM fluid, I first tried tap water, but that foamed
and sputtered away quickly. I then went to alum-tap tapping
fluid, which worked fantastically as an EDM fluid. I set up
for about 30 V open circuit, and started the mill in the slowest
backgear range (80 RPM). With the brazing rod almost perfectly
straight, it orbited about .010 - .015", clearing out a bigger hole
in the tap than the diameter of the rd, itself.

I programmed the CNC to advance the spindle at about .006
to .01" per minute, and used the feed override to keep EDM
current between .25 and .5 Amp. I replenished the fluid as needed,
and raised the electrode and cleaned out the hole when progress
stopped (about every .020"). I got rid of each tap in about 10
to 25 minutes, depending on how much of the tap was left down
in the hole. Mostly, after the EDM operation, all that was left of
the tap was the very tip of the flutes, and they could be picked
out with a fine needle. All the holes were later tapped and
the parts used. An earlier attempt to burn the taps out with
Nitric Acid was not very successful, and left the aluminum
slightly stained, but the EDM did no damage to the workpiece
at all.

I plan to put all this, including diagrams and photos on my
web pages.

Jon

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James P Crombie
Summerside PEI Canada

My Astronomy stuff
RhinoCad 3D Stuff

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