I got an inquiry from woodworker Kent in Canada about the unusual barbed hinge used in the center of my walnut and hickory jewelry box for sale on Etsy.com. This spring hinge, like the other barbed hinges I use on small boxes comes from Craft, Inc. I added the center hinge for additional strength, but it also serves to hold the lid open and stiffens the feel of its operation. It requires additional routing to provide clearance for the spring. I had purchased thousands of these hinges quite a few years ago, then left them in the box as I tried to conceive an easy technique that would allow me to put them to use.
But for Kent, the photo below will help as it illustrates the culmination of years of idle head scratching. He is reading my books and now knows the technique of using stops on the router table fence to control the length and position of a routed slot. The small recess to accommodate the hinge is cut with 3/16" straight cut router bit, raised about 3/16" high above the surface of the router table. This results in a combined 3/8" deep recess in the lid and base of the box, providing clearance for the spring.