Disclaimer: This works well enough, but it is not perfect. It served the purpose that I needed it for which was cutting small circles out of lexan. I included an (untested) v2 version of the base with a larger center hole because the collet on my router ate through the top of the original base.
This is a replacement sub base for the Dewalt DW618 that will allow circles to be cut that are smaller than the diameter of the base, without the need for a pin hole in the center of the work. I was inspired by the following video, which also shows the basic mechanics of how this works: https://www.youtube.com/watch?v=PsV-84kjnVY
The mounting holes are made to fit the plunge base on a Dewalt DW618.
You will need the following hardware:
1x 5mm shelf pin
1x 3/8" bolt
1x 3/8" wingnut
I wanted to route circles out of plexi so I left the liner paper on and used hot glue to attach the block to the liner paper.