*** This post is courtesy of Tom Iovino of Tom’s Workbench ***
The mortise and tenon joint is timeless. Classic. Functional. And, not as difficult to cut as you might imagine.
Oh, sure, if you have never cut one before, you might be scared senseless to start. I mean, don’t you need a shop full of fancy, expensive jigs and unitasking machines? Think about Norm Abram of the New Yankee Workshop. He cut mortises with special fixtures for his drill press or his dedicated hollow chisel mortiser. And, he had his special table saw jig that cut tenons on boards standing on their ends. If you build a lot of projects with numerous mortises and tenons, this is a good way to go. These tools offer a great deal of flexibility and convenience when cranking out these joints all day. But, I would contest that you have one of the best mortise AND tenon cutting systems in your plunge router. Equipped with the right kind of bit, these babies can crank out tight-fitting joinery with little effort.
For mortising, I like to equip my router with an up-spiral bit. Those bits resemble drill bits, with flutes that can eject sawdust from the joint you are excavating, giving you smooth walled mortises of a consistent width and depth. There are many ways you can go about guiding your router to give you the desired results. Here are just a few:
With a template. If you rout a slot in a piece of MDF or plywood at a width that can accept a router bushing, it will guide your router as you cut away. I usually cut a 3/4″ slot to accept a like-sized bushing, then use a 1/2″, 3/8” or 1/4″ bit to cut the appropriately sized mortise.
With a center-finding guide. Special base plates with carefully aligned bearings automatically center your bit on the work piece, locating the mortise in the ideal location for maximum strength.
With your edge guide. By using your edge guide, you can carefully place the bit anywhere along the piece, giving maximum adjustability.
With a table mounted router. Flip your router into a router table, adjust the fence to place the mortise where you want it and lower the work onto the bit and using stop blocks to control the final length of the mortise.
The tenon can be made just as easily with your router. You could cut it on a router table by pushing your work past a straight cutting bit, which is certainly a viable option. However, once I tried a four-faced tenon cutting jig – WOW. That has become my favorite way to cut tenons. Fast, accurate and repeatable.
The jig is very simple to build – it has a flat top piece with a window cut into the top for the router to plunge through. There is also a vertical fin that gets dadoed into the bottom of this top piece. And, finally, there’s a fence that the board you are routing sits against.
Set the depth on a rabbeting bit, and start the router. The length of the tenon is set by the plunge depth of the router, and the depth of cut is set by the guide bearing at the bottom of the bit. Jim McCleary of Proven Woodworking has an outstanding page featuring plans for the jig and videos of how it works.
Yes, the mortise and tenon is a great joint. And, now that you know how to cut both parts with your plunge router, what are you waiting for? Get out there and build!
*** Specials thanks to Tom Iovino, a true Shop Monkey, for this post. He will be providing posts on a monthly basis for Eagle America, check back again soon. ***