Hi Luke:
Here is my take on copper and its uses in EDM:
There are two principal reasons to use it; one is to avoid the mess of cutting graphite and the second is in certain small, low power burns where super fine surface finishes are needed.
If you are doing any volume of burning, the benefits of graphite are hard to overstate, and the things needed to solve the messiness problem are worth doing.
Better wear, better electrode stability, better burn speed...the list goes on.
But for the occasional use like mine, there's a benefit to copper that makes it worth while to accept its limitations, and many shops like mine with a sinker in the corner have made the same calculation with the same result.
The arguments for and against Telco versus C101:
I have come across them before and I checked them out for my own satisfaction years ago. (to the best of my knowledge HDHC copper is C101 but hard drawn)
In my opinion, C101 can be profiled and surfaced without too much pain, but as soon as it comes to drilling flushing holes that are tiny, the difficulties grow alarmingly and it becomes a non-starter because of the unacceptable loss rate of trodes due to drill breakage.
I have not found a process control plan that reduces that risk acceptably; no magic tools, no magic coolant, no magic speeds and feeds, but I confess I didn't try all that hard either.
Telco by contrast is drop dead easy to drill; even small diameter, deep holes are a doddle.
Other benefits are that Telco does not raise the same number or size of burrs and is easier to finish mill to an acceptable standard (but is shitty to turn to a nice finish).
Telco can also be surface and cylindrical ground more easily then C101 and I find it easier to polish as well.
So if you are serious about your EDM efficiency you will use graphite and reserve your copper use for very specific applications.
If you can stomach the cost of POCO Angstrofine graphite for the fine detailed high precision burns with fine finish requirements, the need for copper will be almost non-existent.
You can also use POCO C3 (copper impregnated graphite) if you can stand the taste of it when it permeates the air and makes you feel ill. (at least it does me)
If you are an occasional EDM jockey, you can pick your poison depending on whether you plan to drill flushing holes or not.
If you have a linear motor sinker, you rarely drill them anyway.
If you have a ball screw sinker or a hydraulic ram sinker, you may drill quite a few flushing holes and in that case I would choose Telco.
I found not enough difference in EDM performance to justify the pain of C101, even though the pain was not all THAT much more (except for flushing holes).
The performance differences are not discernable to me... if you want to do noticeably better with your EDM process, graphite is the proper choice, not some marginally better grade of copper.
Cheers
Marcus
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