Subject: EDM machine

From: [email-masked] (Paul Amaranth)
Date: 14 Sep 1994 12:11:16 GMT

I have an opportunity to buy a small edm machine from a local shop.  It
was used to remove broken taps, but they decided it wasn't cost effective
to tie up a worker burning them out.  It comes with a power supply and a head
that mounts in a drill press, comes in a nice blue 'Do-All' box and
they want $300 for it.  I didn't get the model number though.  I did
notice that the power meter was 30 A full scale.

I can think of a number of uses for this, but I'm still waffling.  If
you had this chance, would you buy it?
-- 
Paul Amaranth  Manager User Services - office: (810) 370 4541 (also voicemail)
               (e-mail)     [email-masked]         
   Mosaic page: http://www.acs.oakland.edu/links/amaranth/amaranth.html

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From: [email-masked] (Ken Toews)
Date: Wed, 14 Sep 1994 15:28:51 GMT

If you have to ask you probably dont need it. But on the other hand
if you take one broken tap out of a peice that you spent 10 hours on
a year, it will pay for itself.

No one can answer that one for you.

--
Ken Toews    *       You can rent this space for as little as $25/day
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
.....Stay Hungry, Stay Foolish...Otherwise you'll end up fat and boring.....

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From: [email-masked] (Tim Kirby)
Date: 14 Sep 94 16:11:07 CDT

Paul Amaranth ([email-masked]) wrote:
: I have an opportunity to buy a small edm machine from a local shop...
: ... I can think of a number of uses for this, but I'm still waffling.
: If you had this chance, would you buy it?

Like a shot (assuming my better half didn't get to the cheque book first...)
EDM is the "in thing" these days and you can do a lot of neat stuff other than
burning out taps...

Tim
--
Tim Kirby _________ Cray Research Inc., Eagan, MN, USA __________ [email-masked]
Software Division              System Support                +1-(612)-683-5390
__________________________ Consider it disclaimed ____________________________
If all else fails, Immortality may always be assured by spectacular error(JKG)

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From: [email-masked] (James Kirkpatrick)
Date: 14 Sep 94 17:18:41 MDT

In article <[email-masked]>, 
[email-masked] (Paul Amaranth) writes:

......

|>I can think of a number of uses for this, but I'm still waffling.  If
|>you had this chance, would you buy it?

Hmm, if you had included the phone number of the folks selling this, it
may have immediately turned into a moot point, since I would have grabbed
it.  (just kidding) (or am I :-)  Of course budgetary constraints can
squash even a bargain.

I browsed your Mosaic page; nice machines, especially the Bridgeport.
You might post your results re the interferometer.  My very vague
recollection is that it would measure distance but not direction;
am I wrong?

Jim

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From: [email-masked] (Carl F. Ijames)
Date: Thu, 15 Sep 1994 02:13:29 GMT

In article <[email-masked]>, [email-masked] (James
> recollection is that it would measure distance but not direction;

What I know about interferometers came from learning how Fourier transform
infrared spectrometers work (several years ago), not mills, so if there are
standard tricks in using them on machine tools I don't know them :-). 
Anyway, passing a laser beam through a Michelson interferometer with one
mirror fixed and the other moving results in a sinusoidal variation in
light intensity.  The frequency of this variation is determined by the
wavelength of the laser and the mirror velocity.  Stopping the mirror
yields a constant intensity.  The mirror direction cannot be determined
from this single signal.  In FTIR's, a white light source was passed
through its own interferometer.  This gives a strong signal burst at the
mirror position corresponding to no optical path difference between the two
mirrors and virtually no signal away from this position.  This was used to
set the "mirror zero" on each scan of the moving mirror, and the control
electronics knew which direction it was scanning.  To minimize mechanical
problems the mirror velociy (and thus laser signal frequency) was held
constant with a phase-locked loop.  The problem was at the turn around
points, since the signal frequency fell to zero and it was possible for the
system to miss one or two zero crossings.  That was why the white light
source was necessary to re-sync each scan.

On a mill the frequency would be very low and variable, so detecting zero
crossings would be difficult.  One FTIR solution to the low frequencies
(probably patented :-)) was to attach a piezoelectric crystal to the fixed
mirror and vibrate it.  This superimposed a high frequency signal on the
laser signal, and by detecting whether the laser signal was shifted up or
down in frequency the mirror direction could be determined.  Again, this
would have problems at very low mirror velocities.  One manufacturer wound
a solenoidal magnetic coil around the HeNe laser to cause Zeeman splitting,
giving two laser lines 250 kHz apart.  These give a continuous beat signal
even with no mirror motion, and as before the mirror direction could be
determined by the direction of frequency shift.  Besides giving the mirror
direction, both of these schemes increased the frequency of the signal used
to control mirror velocity, allowing more stable mirror control.

There has been a lot of development in step-scan FTIR in the last few
years, so there are probably better schemes for determining the mirror
position that would be directly usable on a mill.  Unfortunately, I've been
doing mass spectrometry (and no FTIR) the last several years.  Anyway, this
is too long, so I'll stop here and listen for a while :-).

Carl Ijames     [email-masked]

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From: [email-masked] (James Kirkpatrick)
Date: 15 Sep 94 08:20:12 MDT

Well, interferometers have come a long way since I was in high school!
My main concern, regarding direction, was the possibility that the
interferometer might consider certain non-motions to be motion and
therefore indicate a larger distance than was actually traversed.
For example, if a mirror was not perfectly rigid, it might vibrate
due to (say) vibrations conducted through the floor from an unrelated
machine (air conditioner, mill, etc).  Without good direction sensing,
this back-and-forth vibration could result in an idle machine while
the interferometer indicates constant travel.  Another example might
be a sticky cross-slide, that sticks-and-jumps along in very small
steps; this could cause the mirror to vibrate in both directions,
and a simple interferometer would add up the total travel and indicate
a distance larger than the actual distance traversed.

Sounds like this can be avoided, but is it worth the extra electronics?
It certainly sounds interesting, though!

Jim

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From: [email-masked]
Date: 15 Sep 1994 14:16:04 GMT

In article <[email-masked]>, [email-masked] (Carl F. Ijames) writes:...

>standard tricks in using them on machine tools I don't know them :-). 
...
>Carl Ijames     [email-masked]

The interferometers usually used on machine tools generate two colinear beams
which are polarized perpendicular to each other and which have slightly
different frequencies. Hewlett-Packard generates the frequency difference by
Zeemann splitting in a magnetic field, as you describe. Zygo generates the
frequency differenced by passing the laser output through an acousto-optic
transducer, then re-combining the output beams from this. Either method
allows unambiguous determination of direction as well as distance.

The Zygo unit I use allows determination of distance to about 2.49 nanometer
and angle to about 0.01 arcsecond (depends on exactly how they're set up).

                                                    ...when I sit down to write
Don Holly                  my intentions are always blameless however deplorable
                           the ultimate effect of the act may turn out to be.
                                                --Joseph Conrad

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From: [email-masked] (Jack Coats)
Date: Thu, 15 Sep 1994 10:36:14 CDT

I rember building a home-made EDM machine some 20+ years ago with my dad
in our garage.  I think we used plans that were published in Mechanics Ilustrated,
Popular Science, or one of those kind of magazines.

It was a kick to use back then.  It wasn't industrial strength or anything,
just good for learning the principals.

Does anyone know where I could find those plans again?

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From: [email-masked] (James Kirkpatrick)
Date: 16 Sep 94 08:11:40 MDT

In article <[email-masked]>,
[email-masked] (Jack Coats) writes:

|>I rember building a home-made EDM machine some 20+ years ago with my dad
|>in our garage.  I think we used plans that were published in Mechanics Ilustrated,
|>Popular Science, or one of those kind of magazines.
...
|>Does anyone know where I could find those plans again?

That was March 1968 Popular Science, pages 149-153.

It was re-worked in Home Shop Machinist, January 1991, with several
follow-up letters and articles.

See also February and May 1993 Electronics Now.

Note that this machine is very dangerous, electrcially, and also presents
a severe fire hazard if kerosene is used as originally described.  You
have to be careful, and today there are commercial dielectrics that
should be used in place of the kerosene.

Jim

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From: [email-masked] (Bruce Holder)
Date: Fri, 16 Sep 1994 15:54:30 GMT

Paul Amaranth ([email-masked]) wrote:
: I can think of a number of uses for this, but I'm still waffling.  If
: you had this chance, would you buy it?
Instantly!
--
Bruce Holder		[email-masked]
			(303)530-8739