Greetings All,
I used slip tenon joinery for my last furniture project and thought that this technique has some advantages over dowels, which I have been using for a while. Even using a Dowelmax, which is a very well made product, and being as precise as possible, I would still have some slight misalignment of pieces sometimes. Maybe 1/32”, just enough to be problematic, particularly when working with plywood which may not be able to be sanded flush. And the problem with dowels is that there is no room for tweaking to achieve a perfect fit. Once the holes are drilled, that’s it.
I achieved nice results with slip tenons on my last project using a router with a spiral bit in my Moxon vise and an edge guide and stop blocks, but the setup was a bit tedious and not easy to duplicate once broken down. I had to be very careful to make sure that the edge guide was set perfectly square to the work piece. After some research, I decided to make a jig based on the design by Philip Morley, who has an instructional YouTube video and an article in Fine Woodworking:
https://youtu.be/eHIOTXABu60?si=EYu0a0QY4rMx1R1vThe basic concept is using a 5/8” bushing in a matching slot on a sled which rides perfectly square to the slot. The 5/8” bushing allows for 1/4, 3/8, or 1/2” mortises which should be sufficient for every project that I will build. The system is based on marking center lines on your work pieces, which align to center lines on the jig. Stop blocks limit the router travel to define the length of the mortise. The tenons are made by milling stock to length and width, and then rounding the edges with the appropriate round over bit at the router table. The stock is held in place with Microjig dovetail clamps after a grid pattern has been made in the face board. I was on the fence for a long time about buying into this system, but it is fantastic.
This jig is quick to set up, easy to return to previous settings, and most importantly very accurate. I made mine slightly smaller than Morley’s design to conserve valuable wall space in my garage shop. I also made the top from 1/2” plywood instead of 3/4” to make sure that I can make mortises as deep as I like. I highly recommend this jig.