I hadn't used this thing in awhile. I was making something out of the 'junk wood' that LOML brings me from work. Not only is it odd-sized but, I didn't want to use my better cutters on this stuff.
I have a trashed spiral bit and this "Auto-Adjust" jig from days gone by. Just clamp it on, aligning the fixed edge with your desired dado location:
Put a piece of your odd-sized material in; you don't even care what the thickness really is. Lock down the movable jaw:
Run the router back and forth:
Perfect fit on some imperfect material:
I knew I had that jig stashed in the cut-off bin for something .