Hi Mazo:
I definitely agree with Zaki that suction flushing will be a huge help for keeping all the debris from arcing , shorting and taper cutting the pocket.
However, I'd use a different strategy for flushing.
I'd make a rougher that's substantially undersized (say 0.25 mm per side, and blast it into the job with high power, low frequency settings to minimize electrode wear and hack out most of the material quickly.
Put a single decent sized flushing hole into that trode; minimum 3mm diameter and 2 hole diameters off the center of the trode; use it to suction flush as Zaki recommends.
Put the hole at a 45 degree angle for the first 10 mm or so, then connect it with a vertical hole from the back of the electrode.
This is so you don't end up with a long spike at the bottom of the hole.
Once you've roughed to depth with it, dress off the end, index it 180 degrees and go down again to wipe out the residual spike, (that's why you put the hole in off center...the index will present an undrilled part of the trode face for your second burn). flatten the floor, pick out the corners and rough in the walls to within 25 microns or so.
Use a normal orbit for the roughing burn; if you get too crazy with your orbit, the suction flushing will not be even, and you'll have more problems with debris piling up on the electrode.
Your second trode needs no flushing holes; make it substantially smaller than the pocket and vector it into the corners; don't orbit it.
Direct the flow from a flushing wand down each face of the electrode, so make the trode long enough that you can point the wands where you need to to keep the faces washed clean.
If you jump flush and vector diagonally into each corner, you can pick the corners out easily with no problems at all because you have lots of room around the sides of the burn and you're not going very deep...only a few hundred microns (you're mostly burning SIDEWAYS now, not down in Z so the depth of the pocket no longer matters).
That's it; two electrodes and a fairly simple burning strategy, and you should be able to get your pockets as parallel as your electrodes were ground.
You can easily adjust for size and get them perfectly dimensioned too.
Keep your finishes as coarse as you can get away with, to make it easier to hold size and to minimize arcing, and you're good to go.
Cheers
Marcus
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