Cutting mortises and tenons with a router has a lot in common with cutting dovetails or box joints. The b;isic process is to cut a cavity in one piece of wood that will accept a projection that you've cut on another piece. Joining the pieccs is the primary motivation. The big difference is that in mortise-and-tenon joiner)', most of the joint is invisible. That means that as long as the joint is Structurally sound, you don't have to worry too much about cosmetic fit. In fact, with many of today's glues, you're better off to "leave room for the glue." In other words, don't make your joints too tight.
Obviously, that doesn't mean you should be careless. The big requirement of mortise-and-tcnon joinery is stnictural integrity, but a very close second is location during assembly. If your joints are properly cut. you should be able to assemble the unit without glue and have everything fit. You don't want to have to overcome ill-placed parts when you're gluing and clamping. That means that your mortises and tenons not only have to be in the right places but they also have to be cut perpendicular to the same faces.
That's where the router really shines. Given a jig or template to place the cut. the router will make clean, true cuts perpendicular to the surfacc you're working from. So we'll talk about some of the jigs that will let you make joints accurately.
Most mortising jigs are set up to guide the cutting of mortises. You can cut the tenons on the router table, regular or horizontal. The thing is that they'll have square corners, while any mortise you cut with a
This cutaway shows the difference in Jinish between a routed mortise (left) and a chiseled one (right). The differences are immaterial cosmetically, since the insides of the mortises are hidden. But a smooth surface yields a superior glue joint.
An open mortise is a slot through the end of the workpiece. To cut one. use the tenoning sled on the horizontal router table. Set the bit for the final depth of cut, and keep the sled tight against the tahlctop edge for each pass. But for the first pass, hold the work hack from the mounting board so the bit only cuts about '/■» inch deep. After each pass, advance the work toward the router, cutting deeper and deeper.
ing that's possible. The handwork can be minimized—you don't need to clean out the mortises with a chisel, as you do with those roughly formed with a drill bit. And you don't need specialized, single-purpose accessories—like a hollow-chisel mortising attachment—that are so involved to mount and remove. A plunge router, a spiral bit. and an edge guide (or two) will handle most of the monising you'll ever want to do.
The only disadvantage that comes to mind is the limited reach of the router bit. A narrow, deep monise— V4 inch wide by IY* inches or more deep, for example, or Y* inch wide by lYi inches deep—is problematic for a router but relatively easy for a hollow-chisel moriiscr. Willi savvy project design, you can get around this limitation.
Once you try doing some mortise-and-tenon joiner)* using the router, you'll realize how easy it is. And your joiner)' universe will explode!
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