Need Help!- Gibbs machining problem, solutions?

[houdini]

Ok here is the setup, I am using a Milltronics 3 axis VM17.
1-part is 1/8" vacuformed ABS
2-The part has a large pocket 6"L 4" W4"D
3-Walls are tapered about 7-10 degrees.
4-One wall has/needs a square cutout in it.
5-trying to cut it out with a ket cutter 1.25 Dia. .1875 blade thickness. neck is relieved to .5 for 4".

I have tried just setting up a contour entering in the final z depth for bottom of square cutout, top height of the cutout in the top of part parameter location.
problem, I noticed that as I vary the z steps tried .03 per pass from .1875 per pass, it raised the top cut of the square. also because the walls are tapered when I try to cut it I end up with a tapered square. can any one give me a solution to this machining problem.

Thanks CHEERS!

[houdini]

OK Ill answer myself
In setting the top of part param as the top of the square cut out, I had to add the cutters width of the blade(or depth of the blade in this case).1875.
Also the depth of the z steps needs to be subtracted from that depth, to end up with the top of the key cutter ending up at the correct top cut of the square cutout.

then due to the 5 degree on the walls causing the cutout to taper smaller at the top,
I used the angled walls option, since this not only pushed the cutter in deeper at the top, it also made the cutter cut wider at the top this cut compounded the angle needed so a smaller 2+ degree angle was used. I know that that could have been avoided by just cutting a line instead of a in line geo and out line geo, and just setting the 90 line by the amount needed. but too late.

Thanks anyway.