When I was just getting started in moldmaking, one of the jobs that I was tasked to do was to cut gates into S-7 steel hardened to 52-54 rockwell C. We made the single lip sutters with the Deckel grinder and then we would set up in a Bridgeport mill, kicking the core block up to 45 degrees, and then locating the gate location and lock the table down. Then crank the speed up to 2500 rpm and take a 0.001-0.002" cut per peck of the quill. After about 2 holes anyone can do it. The bad part about this is that when you break the tip of a cutter off in the bottom of a gate, you have a hard time getting it out, but this is still quicker than EDM, and it doesn't tie up an EDM, just a mill and a warm body. We would typically do this for the 16, 32, 64, and 128 cavity molds. Either way there are problems, usually when trying to EDM a tunnel gate, or subgate as we called them, you couldn't get the flush to work just right to flush the tip of the electrode so it slowed the burn.
These days I usually try to mill my gates first and only burn them if I have to.
Jim
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