Frame Mortise and Tenon Jig

If you've got a lot of mortise and tenon joinery in your future coming up in your woodworking shop, let me talk a little bit about this jig here. This is the Leigh FMT jig, that stands for frame, mortise and tenon. And it's really specifically designed to be, it's just a beautiful way to make mortise and tenon joints. Here's the way the whole thing works. There are a bunch of different guides that can be used with the jig, and the guides control what size mortise and tenon joint you'll create. So it's clearly marked on the guide what dimension mortise and tenon this one will cut. So by marrying different guides to different sizes of router bits, the jig will allow you to produce a whole variety of mortise and tenon sizes. The guides themselves snap into the top of the jig here. Now, those guides are all about the pins that are in the base here under the router. So I've got my plunge router attached to this FMT base. Here in the base for the jig, there are two pins. And if you have a close look, the pins are actually tapered. And that's part of the beauty of the engineering of this thing. It's the taper that allows you to fine tune the fit of your joint. When those pins engage the guide, the taper is what controls the fit because we're gonna use more or less of the taper, in other words, a wider or smaller part of it. So here's how the whole thing works. When I wanna cut the mortise, the pin will follow just the straight track in those guides, allowing the router to move left and right. Then, I change my boards and allow the pin to go around the outside of the guide, like this. And that's gonna take away everything but the tenon on the ends of my rails. On your material, what you'll need to do is mark the center of the tenon location. So I've got this crosshair on here. There's a cross here on this part of the jig. So I bring that little bull's-eye forward, get the material under that bull's-eye, lock it in place. With this clamp loose, I can then position this table until the bull's-eye here on the jig aligns with the center point of my tenon. Lock the table in place, bring that out of the way. We're just about ready to cut. The depth of our router bit will then control the length of our tenon. So, by tracking around the outside of this guide, I take away the outside of the rail, leaving the tenon in the center. If we were doing a big project, at this stage we'd cut all the rails. What I'm ready for now is a test cut in a leg. So there's a fence in here that guides the rails in place, that's ready to come out. When the leg comes in, I've also got the center of the mortise located on the leg, just like I had the center of the tenon on the rail part. Bring the bull's-eye forward again. With the table loose, I can locate the bull's-eye now over my mortise, lock the table. Now, and this time, I'm just gonna let the pins follow these guides. These cuts result in a round-ended mortise from the router bit. Also, a round-ended tenon, because of the way we followed the guide. Then we can test our fit. That snapped together beautifully. Now, if it doesn't fit for ya, it's an easy adjustment. Thanks to the engineering on the jig. Remember those pins are tapered. As you turn these knobs, they pull those pins up and down. So again, you can use a larger or smaller diameter of the pin, which it allows you to very, very finely micro-adjust the fit of your joint. So, it's a dedicated machine. It's excellent for cutting mortise and tenon. It also allows you to cut angled mortise and tenon, which is difficult to do by really any other means. So if you've got a lot mortise and tenon coming in your shop, the Leigh FMT might be something for you to look at.