Thanks guys!

Mauser...what i did was we have a local furniture mill, one of my buddies works there. He got me the piece of wood (cherry) and rounded it for me...but for the most part i took my piece of slate, traced it, and then found a 3" circle (on duck tape or something) and proceeded to drill (yes drill) it out as much as possible, going about 1" down. I got out all the big pieces and then my nieghbor has a little dremel tool. I took that with some 80 grit paper on a round thing and sanded it out as much as i could...(see pic below for final) as then it was all open in the 3" circle so i guesstimated 1/8" deep and sanded out the lip for the slate. I drilled the holes as shown and then took it to my nieghbor for acceptance (bunch of turkey hunters were there too, they all liked it and the sound) so i just clear coated it and glued the slate in.

Tools involved :
19V Drill and bits of your choice
Dremel Tool with Sanding Bits
Chisel for breaking off big pieces
Tape measure
5.5 hours of a beginner's time

Here's the pic:
(It shows the inside of the finished call.)