More progress this morning. I put the piece that mounts onto the section that holds the cube in my larger machinist vise. I squared it to the vise using a small machinist square. Then I milled the rectangular section down to approx. .200" thick.
Next I had to indicate the center of the 1" hole that is bored into it. I trammed the mill in the Y axis from center location .500" (half the hole diameter), then an additional .250" (half the mill cutter diameter), then .136" more (the distance from the edge of the cube to the edge of the cylindrical part holding the cube). I have said before I am not a machinist. I don't have a DRO yet on my mill, and my CNC portion is not functioning. I have to indicate/locate everything manually using indicators. (Several times I've gotten lost in the math, adding/subtracting radius's, etc..) I milled the top edge, doing climb milling, and going very slowly. I knew that the part was not very secure in the machinist vice.
I went back to center, trammed over to machine the right-hand side. Again, I wanted to use climb milling for a better finish and less burrs. As Joe Pie says on his YT machining channel, "If the chip exceeds the grip, then the part will slip." I had milled maybe .200" and the part jumped in the vise. Luckily nothing was damaged, I just had to go through the aggravation of another setup and indicating everything back in.
Lesson learned, next time do conventional milling to a few thousandths of size and clean up with a climb milling pass. Especially if you have a minimum grip on the part.
I finished up the other 3 sides without incident. The photo is of only the chips from cutting the last side down to size.