Cutting objects apart

 From:  mickelsen
Hi Michael,

In the drawing, you can see a flat plate-like object with a middle piece cut out of it. At least, it's supposed to be cut out. But when I try to select the middle piece to delete it, the whole thing always is selected. I tried to find where they were still connected, and create some cutting surfaces to disconnect them. You can see the cutting surfaces. They are there solely for this trimming/cutting operation. But they don't do the trick either. I suspect that I've done something squirrelly in creating the plate, or with the initial boolean diff that I used to cut the middle piece out. Please note that the sides of the hole that's supposed to be left, are at a non-right angle to the plate itself. This is important.

In any event, can you help me to get that middle piece out of there? I hope that I've explained everything well enough, and that the elements of the drawing are easy to understant.