Originally Posted by
claya
I just bought an Eltee Pulsitron from a retired friend who had an EDM
shop for 30 yrs. Sadly he died last week, before I had a chance to have
him help me with it. I have been around EDM for a decade, but never paid
close enough attention to the setup. So could use all the info/advice
that is available. I own a precision prototype CNC shop, so am pretty
familiar with tool/die work. And have the Eltee running, but not good
enough to add EDM to my shingle yet. I have the book, and a bunch of
spare graphite, electrodes, and 3R holders.
So a whole bunch of basic questions about the Eltee and general sinker EDM:
1. Is there a decent textbook on Sinker EDM? The Eltee book is pretty
good, but it is a little disjointed on the process. Like, set the gap
and gain settings to steady voltage... with a bunch of theory as to
how all the settings are somewhat dynamic... Sometimes the gap/gain
settings make little difference, other-times they make a LOT. Like
to understand why.
2. How do I get it to plunge/retract/plunge? Right now it just plunges
into the material till it gets to the stop depth.
3. How do I determine when the electrode is worn, and time for a new
one? This seems pretty subjective.
4. How can I tell the difference between copper and copper/tungsten? I
have several packs of copper electrode tube. They all look like
copper to me.
5. The book talks about overcut a lot. Is that generally on the ID of
the part?
6. How do I determine spark gap, and how to undersize the electrode? Is
there a rule of thumb, or formula based on amperage/on time?
7. Do all electrode materials use the same spark gap rule?
8. I have the 6-7 pages of electrode/material combinations. Why are
there 7-8 test cuts? Am I supposed to interpolate the settings based
on the test cut parameters?
9. Do any of you have a notebook of material/electrode combinations you
can share? We do a-lot of stainless, and also copper/nickel alloys.
10. What would be a good electrode material for copper/nickel?
11. I called Freedom Tech, and the phone just rings and rings. Since
Frank B. died, is anyone still running the place?
12. How critical is flushing pressure? I am replacing the pressure gauge
with a much narrower range so I can control down to 0.5psi. Do you
normally just set the flushing flow to where you can tell by eye it
is enough?
13. I have the Vectoring head. is it better to just use orbiting to
control fine finishing of ID surfaces? We have a project where we
need to get to 16uin surface finish.
14. How do we determine the best graphite grades to use? I understand
grain size, etc.. but This seems like black magic along with most of
the Sinker process.
15. How do we use the capacitor bank switches to improve finishes?
16. Do you have a fume hood above the sinker to capture the smoke/fumes?
I have never been there during heavy roughing jobs, so no idea if
lots of smoke is normal, or we just had the tank/fluid level too
low. We were aggressively roughing some aluminum and there was
copious smoke.
17. We need to cut a very small 90° tapered seat (In copper/nickel).
Also with a 16uin finish. Is it best to orbit that cut, and use the
slurry to get us that finish? Or are we better off machining that
feature conventionally using a chamfering tool on a VMC?
18. How do I know when dielectric is going bad?
19. On the Eltee, the fill valve never closes off the tank flow
completely. Is that normal, or is there a bad seal (O-ring) in the
valve manifold? \
20. The Vacuum line seems to always pull a low vacuum. Is that a bad
seal? Or Normal? We have the vacuum ball valve in the tank set to
halfway like the book says.
21. The tank catch tray does not drain very well. Is that normal? Should
I plumb the catch tray into the vacuum line?
22. Does the Futaba DRO have decent battery backup? I'd like to leave
the origin sets in the DRO, so I don't have to re-indicate at each
power-on.
23. Lastly, we have a very challenging internal o-ring undercut project
that comes back once a year or so, in Inconel 718. For a -004 o-ring
groove. So the electrodes are VERY fragile. Could use some sage
advice for that. We currently use a great EDM shop for that feature,
but hope to bring the operation in-house to help pay for this machine.
Eltee Pulsitron and general sinker EDM questions.
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