Do you have trouble setting the exact corner of your square material? Here is a neat little jig I just made. You can also use it as a Z zero indicator as long as you know the thickness off your material, as used with Mach 3. This one is made of plastic as a test.
First setup your machine to use the jig and the bit as shown in the Troubleshooting Tips - viewtopic.php?f=11&t=1968#p5038 for your Auto Zero
Once you have this made of aluminum, you can slide the jig over the corner of your material to cut, move the bit down into the hole just far enough so the bit will touch the sides of the hole then run the routine in Mach 3 to find the center of the corner. This will center the bit over the exact corner of the material so you can then use this as your 0,0 home position.
I also included the cad file as a zip file since we can't upload the dwg file.
If you use a 1" piece of material and flip the piece over, you can cut out the inverse of the design and also use for inside corner location.