Leigh Mortise-and-Tenon Jig

The FMT system consists of the tablelike fixture that holds the workpiece; a set of #20-biscuit-size interchangeable router guides; and a subbase that mounts to virtually any plunge router. (It took me about 30 minutes to install the subbase on my old Ryobi 1-hp router. But with that done, it takes only seconds to remove or reinstall it, so I still can use my router for other chores.) That subbase has two guide pins on the bottom. One rides in a permanent slot on top of the fixture; the other runs either in the slot of the router guide (when routing the mortise) or around the perimeter of the guide (when routing the tenon). You use the same upcut spiral bit and cutting depth to machine both parts of the joint. I like the slide-away centering sight that perfectly aligns the mortise or tenon. The first joint I made with the FMT fit so well that when I pulled it apart, it made a “pop!” like a cork coming out of a bottle. That’s a little too perfect for a glue joint, so I tweaked the fit with the on-board adjustment knob that resizes the joint components in .001" increments. A couple of clicks later, I remachined the pieces to a just-right fit. The FMT comes with five guides that will make more than 20 sizes of mortises and tenons using only the 5/16" spiral bit that comes with the system. You can buy additional guide sets and make different adjustments to stops on the fixture to create an almost infinite variety of mortise-and-tenon joints, including angled joints, in workpieces up to 3" thick and 5-1/2" wide. I’ve only scratched the surface of the FMT’s capabilities. I’d encourage you to visit Leigh’s Web site to learn more. It may be more jig than many woodworkers need (just as a Mercedes is more car than I need), but what a sweet ride it is. —Tested by Paul McClannahan