The mortise and tenon joint has enjoyed a long, illustrious reign as the hallmark of fine craftsmanship in just about any area of furniture making you can name. There just isn’t a better, more reliable way to join chair legs to rails, table legs to aprons, or for that matter, the members of any frame construction. Given that, and the fact that traditional mortise and tenon joinery techniques are on the difficult and time consuming end of the scale, it’s no surprise that efforts to design tools and jigs that make the joint faster continue to this day.
And some great solutions have come along. For traditional mortise and tenon joinery, it’s pretty tough to beat a tricked out router jig like the Leigh FMT Frame Mortise and Tenon Jig and a plunge router. With a relatively fast set up, easy calibration of the mortise-to-tenon fit and an impressive library of joint guide templates, the Leigh jig has made a name for itself among woodworkers who take mortise and tenon joinery seriously.
Then there’s Festool’s revolutionary Domino Joinery System. If you’ve thumbed through a woodworking magazine in recent history, you’ve almost certainly seen at least one picture of the Domino joiner. But in case you haven’t, the tool bears a striking resemblance to a biscuit joiner, and operates in a similar way. That’s really its claim to fame: The Domino is as quick and easy to use as a biscuit joiner, but instead cuts mortises that are perfectly matched to Festool’s proprietary “Domino” loose tenons. The result is a joint that’s arguably every bit as strong as a traditional mortise and tenon joint in the time that it takes to pop in a biscuit or two.
If there’s a problem with these two solutions, though, it has to do with cost. Not every woodworker can justify the investment in a $700-plus gadget that doesn’t do anything other than make really great mortise and tenon joints. Woodworkers who are still building a collection of the basic equipment, along with those who only occasionally need to cut a mortise and tenon, will undoubtedly be in the market for a more affordable solution. And for them, we think we have just the thing. Recently, Rockler teamed up with Incra Tools, to develop the STS Slot Mortiser Kit, a router table jig that brings accurate, repeatable mortise and tenon joinery in reach of the most budget-conscious woodworker.
Like the Domino, the STS produces a loose tenon joint, a joint type that continues to gain on the traditional mortise and tenon because of its relative ease and comparable joint strength. The loose tenon method essentially cuts that joiner’s work in half. All of the tenon stock for an entire project can be made in a couple of table saw rips, a quick (essentially optional) pass through a planer and a little rounding off of the edges. After that, the challenge is simply to cut one identical mortise after another, cut the tenon stock to length, and fit the parts together.
Cutting mortises on a router table is nothing new, but it’s never been an extremely poplar choice. That’s because the usual router table method – using the fence as a guide and dropping the stock into the cut from above the bit - comes with a couple of serious problems: First, getting the mortise in the right spot can be a surprising challenge. In many cases, set up involves multiple fence and stop block positions each of which can be nearly impossible to repeat. When you consider the fact that an average furniture making project can easily require a couple dozen mortises, constant set up problems are more than a minor nuisance.
The STS Slot Mortiser solves this by providing positioning scales for both the mortise length stop blocks, and for the distance of the integrated fence from that bit. Setting the width and depth of cut takes only a few seconds, and you can return to a position for repeat cuts reliably and just as fast.
Another problem with router table mortising has to do with starting the cut. Typically, the procedure for cutting long-grain mortises on a router table is to butt one end of the stock up against a stop block, and move the stock down slowly onto the spinning bit from above. Doing this, however, can be a little unnerving, even if you follow the safety rules and make the cut in a number passes. Cutting corresponding mortises in the end of a board is another matter – Cutting an end-mortise on a router table, in most situations, is virtually impossible without a special jig.
The STS system’s answer to this problem is to take advantage of the recent boom in the popularity of the router lifts. Instead of bringing the stock to the bit, you bring the bit upwards into the stock while it is securely clamped into the stable and substantial STS Mortiser. The procedure still requires several passes to complete a mortise, but the difference is that it takes only a couple of seconds to raise the bit each time. Also, since the jig is guided by the by the router table’s miter slot - instead of relying on your steady hand maintain firm between the stock and the fence – each successive pass is guaranteed to repeat the exact same cut width and length.
The catch to all of this is, of course, that you have to have a router table equipped with a router that allows depth adjustments from the top of the table. Still, if you had to start from scratch, you could put together a router table package, add a suitable router, and get the STS Slot Mortiser Kit for virtually the same investment as one of the premium mortise and tenon solutions. Given the woodworking versatility a router table adds to a shop, it should be pretty easy for anyone who’s still building a collection of basic tools to decide which makes more sense.
NOTE: The STS Slot Mortiser is no longer available.