- [voiceover] the wood whispereris sponsored by powermatic. - today, i'm gonna show you how to make a double mortise and tenon joint. why? because it's awesome. (funky jazz)
woodworking joints plans, the classic mortise and tenon joint is a hallmark of high-quality furniture, but there are some cases where a double mortise and tenon couldoffer some benefits.
in larger work pieces, such as these, a double mortise and tenonjoint actually offers twice as much surface area for the glue, so instead of just havingthese outside cheeks as glue surfaces, you now have two inside cheeks in addition. and that could very wellmake the joint stronger. just like any other joint, there are a lot of different waysthat you can cut it,
but we're gonna use therouter to do the mortise, and the table saw to do the tenon. let's start with that mortise. now, the first thing i need to do is lay out the mortise, so i'm just using one of my tenon pieces here to mark the start and stoppoint of the work piece, and now i need to drawin all of my shoulders, what'll essentially bethe tenon shoulders later.
but this mortise is gonna start at 3/8ths of an inch in from each edge, and 3/8ths of an inch from the outside edge of the work piece. this is the area thatwe'll be doing our routing, and we stop at these inner lines. now, i want a 3/8ths inch mortise, so i've got a 3/8thsinch router bit in here, and of course an edge guide, which is
gonna help me set it the right distance from the edge of the work piece. and it's really just a matterof pushing the bit down, making contact with the work piece, and lining it up with the pencil lines. (router whirs) now, i stopped here because i wanted to show you, this is areally cool technique that i like to use when routing mortises,
and that is to plunge at the beginning, so i get pretty close to my line, and then plunge at the end. what this does is it gives me a nice area where it's very clearwhere i'm hitting wood, and then once i feel therouter hit open space, i know i'm done. if you don't do that, a lot of times you can very easily go way over your line,
because every single time you route, as you're going deeper and deeper, you have a chance ofgoing over, all right, so this a way to ensure that you don't. let's get back to it. now you see the magic withthat process is the fact that the edge guide isin a fixed position. nothing moves, so we makeone mortise from one side, flip the piece over,and make the other one
from the other side, and that ensures that they're both equally distant from these outside edges,so it makes it perfect. now, at this point, you would wanna cut all these double mortisesthroughout your project; you probably have more than one to do, so you'll wanna cut them all, and then, this is where the magic happens, you want to grab a second piece
that's sort of a pieceof scrap, that's exactly the same dimensions asyour actual work pieces, because what we need to do is remove the center section justfor the sake of setup. all right, so you would changeyour router at that point, and again, you've alreadycut all of your mortises, so it's okay to change this router setup if you're thinking interms of a larger project. all right, so change thesetup so that the router bit
is now cutting in thecenter of that joint, and you'll clear it out and it will look something like this, and this is what we're gonna use for our initial setup. so, let me just grab a tenonpiece and we'll get started. i'm just gonna bring my tenon stock right over that test mortise, make sure it's nice and flush on the outside edges, and then mark the outerwalls of the mortise.
now, i'm gonna use asharpie here, but obviously, you'd want to use a fine pencil for this. so, i've just got my cutting gauge here, and i'm gonna use that to establish a nice cut line all theway around the perimeter. that's gonna sever the grain, and even though we'regonna use the table saw, it's really gonna help us get a nice, clean cut with no tear-out.
(gauge scrapes) the first series of cuts at the table saw will be all the way around the work piece to create the shoulder, soi need my blade to be set at that pencil line, orjust a little bit below. and now i'm gonna bring the fence in to set the shoulder cut. now the miter gauge isgonna hold the work piece nice and steady, 90 degrees to the fence,
and we can make all four of the cuts. (blade whirs) and once again, thinking interms of a larger project, you would wanna make thesecuts on all of your tenon work pieces before youmonkey with the setup. all right, so we're gonnaassume that that work was done, and i can move my fence out of the way, and get ready for the next set of cuts. okay, we're done withour miter gauge here.
and now we bring inwhat i call "big daddy." this is my tenoning jig. it's a pretty straightforward device. basically, the work piece isheld up against this plate, you've got a fence in the back that is adjustable for various angles, but mine is set 90 degrees to the table, and it's got a built-inclamping mechanism. it's very easy to adjust the plate
back and forth to make very precise cuts. now, you can make somethinglike this yourself; i'll even link to a couple of plans in the show notes ifyou're interested in that, but you can make them so that they ride on your table saw fence. this one rides in the miter slot. now, before we can actually use that jig, we need to raise our blade height,
just so that it's going tothe end of this shoulder. you could probably go a little bit shy. you certainly don't want to cutinto this shoulder material. now i'm gonna secure the work piece into the tenoning jig, and bring it right up to the blade. now, just gonna adjust the jig so that the blade is cutting just on the outside of this line.
that looks pretty good. my lines are fat, so idon't wanna over-cut, i'd rather have to cut twice. all right, so i'm gonnamake one cut on this side, and then flip the work piece and make a second cut on the other side. now, we'll do a testfit on the open mortise, and that's a little bit snug,so we'll adjust the jig, and make a second round of cuts.
now, we'll do a test fit. that's not bad. that may be just a hair loose, but honestly, i could live with that. so, now that we have that dialed in, we're gonna cut the piece this way to get rid of the short shoulders. now, once again, if you're batching out, you're gonna wanna doall of your tenon pieces
and catch them up to this point before you change yoursetting at the table saw. all right, so, if we want tomove on to the next phase, we just line up this tenon with one of our actual double mortises,make sure it's pretty well-lined-up with the outside edges, and then you wanna mark the location of the inner walls here. doesn't have to be perfect.
we're gonna sneak up on it just like we did with the outside cheeks. (blade scrapes and whirs) let's do a test fit. okay, normally, (laughs)normally, that doesn't happen. this is the problemwith fat pencil lines is i thought i was leaving alittle extra stock there, but it turns out i wasa little bit tighter than anticipated becausethat is a perfect fit.
check it out. (wood slides) oh man, that's nice. all right, so we do have alittle bit of cleanup to do. let's head back to the workbench. now, you'll very likelyhave some residual material in the inside cornershere, which you could very easily remove with a downward chop and a chop inward like this,but the biggest offender
is likely to be the spacebetween the two tenons, so you just need a narrow chisel, you'll be able to remove that. (chisel scrapes) and if you have any unevennessin your shoulders here, you can usually feel it with your fingers, this is a great job for a shoulder plane. (scrapes) so, a little bit ofcleanup here should do it.
so, now let's do our final test fit here, and see how we did. (wood slides smoothly) oh, yeah, that is nice. now, this isn't really the kind of joint that you're gonna bust outon every single project, but, if you have somethingwith large work pieces where you have enough realestate in the material to make a double mortise and tenon joint.
i don't think there's anything wrong with getting double the surface area for that glue to bind to. and now that you know how to do it, you could show it off toyour family and friends, and then put it into a holewhere no one will ever see it. it's my favorite thingabout joinery. (laughs) all right, so give it a shot. double mortise and tenon'spretty cool, another step
on your way to becominga woodworking ninja. (gentle acoustic music)