Self-Centering Plunge Router Base

A plunge router is great for cutting mortises on the edge of a workpiece. The only trick is getting it centered. Here's a handy auxiliary base that will center the bit automatically, and it works with workpieces of just about any thickness.

The key is a couple of pins. These are nothing more than common bolts with their heads cut off. I fastened them to the base with T-nuts and hex nuts, but for the base to work, these pins have to be positioned carefully. The centerpoint of the bolts and the router bit must form a straight line. Plus, the pins must be the same distance away from the bit. 

To use the base, simply attach your router and set the base on the edge of the work-piece. Twisting the base so the pins contact each face of the piece automatically centers the bit, as you can see in the details at bottom right. Then just plunge and rout the mortise.