[CAD_CAM_EDM_DRO] Drilling out taps (was Simple EDM schematics)

Greg Nuspel wrote:

>
> I have found that some times a broken carbide end mill can be ground
> with a pointed chisel point on the end.

Long shot here for most list members, but if you happen to know a mold
maker with a single lip cutter grinder, bribe him into helping you make
up some tap drills. I'm sure there's different configurations, but I was
taught to grind to a few thou under tap drill dia, split the cutter only
part way (that is, grind the cutting portion to a half circle) leaving a
stout solid shank. Only want a few degrees side clearance.
Grind bottom flat with maybe 5 degrees clearance, and relieve the
non-cutting side of the bottom.
Start with fractional size carbide shanks for which you have collets, or
silver solder them into steel shanks that you can hold in a collet.
Don't try this will a drill chuck.

I virtually always tap in the mill, so when I break a tap I'm already
over the hole. If you broke the tap hand tapping, you will need to setup
in the mill directly over the hole.
Either use the quill stop to control depth, or the knee, and peck a
couple thou at a time. I've drilled out #4 through #10 taps this way.
It works real slick and doesn't damage the hole at all.
If your carbide shanks are long enough, try to grind each end the same
so you'll have an extra.

Jon