Re: Burning out taps in a milling machine

Russell Dunn wrote:

> From: Russell Dunn <russelld@...>
>
> 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.

First, I started with the spindle not rotating, and just hooked an alligator
clip to the electrode. When I decided to make the electrode rotate, I took
sone strands of stranded wire and wrapped them 3 times around the electrode,
and held that in the clip. This worked fine, with no sparking.

Current was about .25 to .5 amp, but would go up to 1 to 1.5 Amp if the
electrode shorted out to the work. that meant that the fluid was gunked up
with burned metal, and the hole needed to be cleaned out and refilled with
fluid.

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

Oh, that would be a bad idea, especialy with what bridgeport bearings cost!

From my original post :

> 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.

Note the Nylon Spacer - that was a 1/2" OD cylinder of nylon with an
axial threaded hole in it. The nylon is the insulator, and the EDM power is
applied to the electrode, below this insulator. The workpiece is held
plainly in the vise, and thereby grounded to the machine. Another clip
is attached to any convenient place on the work - or the vise, if there's
no place to grab on to the work.

I took pictures of this with my digital camera, but the darn thing has a
separate viewfinder, and the parallax is so bad at close distances that
I got a picture of nothing, with just a tiny bit of the electrode in the
image. I will set up a reenactment and take better pictures, and post that
with circuit diagrams on my web pages.

Jon