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Graphite question

Robert Learned

Plastic
Joined
Aug 2, 2017
looking for a graphite that has the least amount of flex. Working with tight tolerances the thickness is .050 x .360 and the depth is 1.400. The readings vary from the bottom start at .000 to the top of electrode.006 currently using CP3000 graphite. Any help would be appreciated.
 
Hi Robert:
All graphite is pretty rigid and 0.050" thick is not particularly skinny, so I'm not quite sure where you're having your problem.
Is it in fabricating the electrode?
Is it in deflection of the trode during use?

In any event, the finest grade of graphite I know of is POCO Angstrofine...very wear resistant, capable of holding very fine detail and super expensive to buy.

The other graphite grade often used by moldmakers for burns like deep ribs is POCO C3 copper impregnated graphite.
It's heavier than straight graphite and seems to have been the Go-To choice before Angstrofine came along.

I haven't used graphite for trodes for many years, however I remember that grinding C3 was a special pain in the ass; not because it was hard to grind but because it left a really nasty aftertaste if you breathed it in, and you'd get an unpleasant whiff even if you wore a respirator but forgot to blow yourself down with an air hose before you took the respirator off.
Even the vacuum system we had where I worked was not enough to keep that damned smell at bay.

Others didn't bitch and whine as much as I did, so maybe I was hypersensitive to it, but I sure hated that shit!!

It did however, make great electrodes!
Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com
 
For grinding thin electrodes, I sometimes use a Finger fixture, with a variable weight, same one I use to kill vibration in thin round parts when grinding in a spin fixture. A little experimenting with the finger fixture and a tenth DTI will usually get better results.
If the deflection is happening during the burn, you may have to really cut back the pressure, or pulse the flush on the retract.
I agree on the AF5 Angstrofine graphite... Good stuff... I also agree about the nasty taste of C3, it cannot be healthy to breathe.

On edit, .050 X 1.4 long is really going to be tough, I do not envy you.. Any chance of splitting/inserting this detail?
 
Stay away from C3, the copper gives it flexibility on thinner ribs.

How are you manufacturing your electrode and what type of edm are you using?? A rib .050" x .350" should be simple at only 1.4" deep.
 
This rib should not be a problem, but care must be taken when both machining the electrode and the detail. Are you milling or grinding the electrode?
Poco EDM-3 or EDM-4 will work for this application. When it comes to EDMing the detail you are seeing the results from the hydraulic pressures of the oil when orbiting to get your finish and size.Try slowing down your servo speed and jump cycle speed. If you can also change the type of orbit from a circular to a square or vector pattern. You can always contact Poco to talk to one of their EDM Applications Specialist.
 
looking for a graphite that has the least amount of flex. Working with tight tolerances the thickness is .050 x .360 and the depth is 1.400. The readings vary from the bottom start at .000 to the top of electrode.006 currently using CP3000 graphite. Any help would be appreciated.

Are you describing the electrode you have manufactured or a cavity you have burned?

I ask because if you are describing a cavity, you may be experiencing a bit of secondary discharge as debris leaves the cavity. There are a lot of ways to approach this, such as grinding back-taper on the electrode, or alternate flushing arrangements. I think a little more information would help folks here help you more.
 
I haven't used graphite for trodes for many years...

Marcus,

A little off topic, but I am interested in what you typically use for electrodes, is it all copper or copper tungsten materials? Your work is similar scale to some of the stuff I am looking to do, so I am a bit curious.
 
Hi newtonsapple:
I use mostly tellurium copper (Telco).
I use copper tungsten too but it's so damned expensive it gets used only where I really need it.
I don't use graphite because I'm not set up to cut it without making a huge mess.
I miss its performance sometimes, but I don't miss the black crap up my noseholes at all!!

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com
 
Hi newtonsapple:
I use mostly tellurium copper (Telco).
I use copper tungsten too but it's so damned expensive it gets used only where I really need it.
I don't use graphite because I'm not set up to cut it without making a huge mess.
I miss its performance sometimes, but I don't miss the black crap up my noseholes at all!!

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com

Thanks, still working out my plans, but pretty scared of the graphite mess.

NOOB question, but besides machining speed and burrs, what are the "performance benefits" graphite might have with your work?

Fortunately from a cost standpoint, most of my work can be done with sub .25" x .75" rod as the starting electrode material.
 
Hi again newtonsapple:
Graphite sublimates at high temperature; much higher than copper melts at.
That allows you to put more energy into the electrode without trashing it, and that translates to faster burn times; twice as fast or more.
So if you have good housekeeping (and it has to be VERY good) your performance gains are huge when you have to make money at your sinker work and are competing with others for that work.

For the work I do, just having the equipment sets me apart from my competitors, and the time I invest in a job is almost never all about sinker time; it's about soup to nuts service, or design ingenuity, or exotic processes like laser welding, or specialist expertise like my clinical background (I was a dentist once upon a time and much of what I do is dental product development)
So I don't have to care like an EDM shop has to care; maybe you won't have to either.

Having said that; what I do is hopelessly inefficient when compared to a proper EDM shop using modern, state of the art gear and graphite electrodes.
That's why they put up with the dust, and the cost of special graphite milling machines, and the enormous cost in diamond coated cutters and on and on.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com
 








 
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