"Brian Lawson" wrote in message
...
On Tue, 13 Dec 2005 23:17:01 -0500, "Ed Huntress"
wrote:

SNIP
They do catch on fire if you get a little loose with your
shop hygiene. They also catch on fire sometimes, anyway. And don't put
one
in a basement shop. Your whole house will stink of hydrocarbon fumes.

Not sure what you mean by "shop hygiene", but poorly filtered dirty
EDM fluid does seem more prone, but maybe that's because the currents
are higher?

I don't know what, specifically, makes dirty dielectric more prone to fires.
But I was talking more about spills and films of dielectric oil on the
machine. They spread the fire quickly.


Commercial EDM oils don't instantly "catch fire", but rather start
with little puffs of wispy flames of hot vapours bubbling up in a
flooded tank operation, or surface flames-ups for a few seconds in
surface flooding burns. Left long enough, there will be a fire, but
not instantly. That's why most EDM's have a "flame sensor" in the
safety circuit, providing some bozo hasn't jumped it out or turned it
to face away from the work area.

Two caveats: First, most EDM fires appear to start when the work is NOT
properly flooded and submerged -- something that neophytes are prone to do.
Second, a lot of small-time EDMers have used kerosene for EDM fluid, and
some probably still do. Someone who doesn't know the story, told that
kerosene is an effective EDM dielectric (it is), might be inclined to try
it. It also makes a great fire starter and a fast ride to burning your shop
down.

Here's something a European EDM sales exec once told me, that I'll never
forget. He was in charge of his company's business in developing countries
in Asia. "I never have trouble finding the EDM shops in a city in that part
of the world," he told me. "Just before the plane lands, I look for the
columns of smoke..."

They may have a completely fireproof oil-based EDM dielectric now (I have no
idea), but the ones I have experience with were flame *retardant*, and not
flameproof. They're hard to get started but they will burn.

Kerosene is a greater real hazard, and it "stinks".

The commercial dielectrics doubtless have improved since I was involved in
EDM, but we used the best stuff that money could buy. Running our machines
'round the clock, the kerosene or related smell built up, despite the
deodorizing and odor-masking stuff they put in it.


Water as a dielectric won't catch fire, but doesn't carry heat and
swarf as well either.

Well, actually it does conduct heat much better than oil. But you need a
power supply designed for it, and it has its limitations in sinker-type EDM
work. I doubt if you could run a D10 with water...at least, for very long.

--
Ed Huntress