Re: Burning out taps in a milling machine

Hi Jon,

There is one part of your description that is, I think, missing and it is
the part I would like more info on please. How did you route the electric
current from it's source to the brazing rod electrode, and how many amps are
we talking about here please.

I would think that you did not pass the current through the machine bearings
and your alternative path is of real interest to me.

Kind regards,
Russell Dunn
near Newman,
Western Australia

> ----------
> From: Jon Elson[SMTP:jmelson@...]
> Sent: Saturday, 8 May 1999 12:58
> To: CAD_CAM_EDM_DRO@onelist.com; jmelson@...
> Subject: [CAD_CAM_EDM_DRO] intro update
>
> 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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