An FMT and a 1/2" plunge router (not included) can turn your shop into a mortise & tenon factory!

Leigh FMT: Frame Mortise & Tenon Jig

If you're not already using mortise and tenon joinery in everything you build, this amazing jig from Leigh Industries might well change the way you do woodworking, just because it's so interesting to use. On the other hand, if you're already committed to sound solid wood joinery, Leigh's FMT jig can not only turbocharge the process but almost certainly will produce tighter, stronger joints into the bargain.

In some ways the Leigh FMT jig is similar to Leigh's hugely successful D-4 Dovetail Jig. In your first five-second glance at the Leigh FMT, it can seem bewilderingly complex and surely difficult to use -- but it's not. The Leigh FMT jig itself is a remarkable feat of design and engineering, but operation is just plain simple. Understanding basic operation, one step at a time, takes anywhere from five to ten minutes; it's easier than learning to use a wristwatch. Both mortising and tenoning are fully template guided, and the system lets the tweak of a knob adjust the fit of your joints in increments as small as you can measure (with a micrometer, that is). Setup is so quick and operation so easy that the Leigh FMT jig is just as practical for making one-of-a-kind joints as it is for high volume production.

Mount Your Router
Mounting your router on the extended subbase that comes with the Leigh FMT jig might take thirty minutes the first time out, but thereafter you'll spend no more than thirty seconds switching from hand held to jig mode or back again. Most router models are secured with rods clamped through the edge guide holes in the base -- no disassembly of the machine, no screw holes to drill. A centering mandrel makes very accurate concentric alignment virtually foolproof.

Mortises
Routing mortises is stunningly easy. Start by marking the center of each mortise to be cut on one workpiece. Identical workpieces can be set to stops or reference marks on shop-made outriggers, with no further marking required. Clamp the stock under the Leigh FMT jig's 3" x 5" work opening, then move the table surface to center a crossline sight over the mortise's center mark. Snap a joint guide into the work table and install the matching spiral end mill bit in your plunge router. Set two guide pins in the subbase into a track on the right and the joint guide on the left, and dial the tapered pins up or down as needed for easy movement with no loose play. Set depth of cut and  plunge rout the mortise. You are done! That really is all there is to it.

Tenons
To cut a tenon, or a hundred alike, mark the center of the tenon on one end of one workpiece, then secure the workpiece against the Leigh FMT jig's vertical clamp plate with built-in cam clamps. Move the work table to center the crossline sight over the tenon. Put the router on the work table and set depth of cut. Rout the tenon. Check the fit, and adjust as needed by turning a guide pin knob. Two or three trials produces a perfect fit, and you're done. Once again, that's all there is to it. The Leigh FMT jig's clamp plate tilts up to 30°, and the tenon side stop fence can be angled left or right up to 45°, so angled and compound joints can be set up and cut as easily as straight ones. As soon as you're familiar with the basics, you can move quickly onward to multiples: side by side or tandem mortises & tenons, triples or quads, whatever a joint design calls for, cutting all of them as easily and precisely as a single joint.

Capacities
Since the work table can be moved both side to side and in & out, with precisely adjustable stops controlling both dimensions, you can work on an area as large as 3" x 5" without unclamping and repositioning the workpiece.
The Leigh FMT jig comes with five 5/16" joint guides and a 5/16" HSS up-cut spiral end mill bit, so you're ready to cut 5/16" mortises and tenons in lengths of 1/2", 3/4", 1", 1-1/4" or 1-1/2".
By using the side-to-side stops on the work table, you can make joints up to nearly twice the length of whichever Joint Guide you're using. The longest 5/16" joint, for instance, is almost 3"; 3/8" and 1/2" joints can be up to nearly 5" long. Furthermore, you can expand the Leigh FMT jig's range considerably by using smaller bits for the mortises and larger bits for the tenons with any given Joint Guide set. Up to 47 custom joints can be produced just as accurately and repeatably as the standard sizes, down to a tiny 1/16" x 1/8". Maximum mortise depth depends on the cutting length of the bit you're using, and (with 1/2" bits) your router's plunge range.

Options
Joint Guides for other tenon sizes are sold in sets for 1/4", 3/8" and 1/2" joints. Given the flexibility afforded by varying the bit sizes and moving the work table, the complete array of joint guides for the Leigh FMT jig can cut a total of 68 different joint sizes (using 8 sizes of spiral bits, 1/16" to 1/2"), from an incredible 1/16" x 1/8" to 1/2" x 5". Each guide set comes with a storage stand.

Additional Information