A Simple Finger Joint Jig for the Router Table

This simple jig makes cutting finger joints on box corners fairly simple to set up on a router table.  Variations can be made quickly for fingers of different sizes. 

It uses a piece of 3/8" x 3/8" x 12" long steel key stock, embedded 1/8" deep in a piece of 12mm birch plywood. This provides a guide rail for making the repeated stepped cuts for finger joints.  

Backboard Sled

The backboard sled has a slot cut in the bottom which sets over and slides on the key stock rail.  The center flange of this sled helps keep the sled square and face vertical. Join it to the bottom and face with French dovetails.  It can have a hand hold cut in it and the shape rounded for a more comfortable hold. 

Center Flange with Handle

A 3/8" spiral end mill peeks through a hole in the base which is slightly larger and 3/8" away from the rail.  Clamp the base down to the router table top on two opposite corners. Adjust the bit height to match the thickness of the boards above the base.  To adjust bit spacing from key stock loosen one clamp and bump the base slightly. 

Base with Key Stock Rail. 

To help the jig work smoothly apply some paste wax to the sliding surfaces.

Jigs for smaller or larger fingers can be made using key stock to match the router bit diameter. 1/4" key stock for 1/4" fingers.  1/2" key stock for 1/2" fingers. 

Amazon.com: 3/8" x 3/8" x 12" keystock.