(jazzy music) Marc Spagnuolo: I'm your
host Marc Spagnuolo. Today we're going to learn
about one the most important joints in woodworking,
the mortise and tenon. The mortise and tenon joint
is one of the strongest joints in woodworking and it's a
joint that you should probably master if you want to make
high quality furniture. Chairs, tables, doors, cabinets and tons of other pieces will all
benefit from the strength of a mortise and tenon joint. If you ever plan on making something in the mission style,
well you better get ready to become intimately
familiar with this joint. Check out this mission
style entertainment center that I built a few years ago. If you can believe it,
that's something that required 82 mortise and tenon joints. So what is a mortise and tenon joint? Well, for anyone who might now know, this is a mortise and this is a tenon. The tenon fits nice and
snug into the mortise creating a really tight and secure joint. Now why is a mortise and
tenon such a strong joint? Well, the simple fact
that we're inserting one part of a board into another board gives the joint a lot of strength. In addition, this joint
creates a significant amount of long grain to long grain
glue surface, which is really the best case scenario
when using wood glue. Now before going into detail
on mortise and tenons, let's quickly take a
look at some alternatives that you might be tempted to try. First, there's nothing. You can actually try to do a
simple butt joint like this, but that's never a really
good idea since the end grain sucks up the glue and leaves
us with a glue starved joint. That's not good for anybody. Next you might consider using biscuits. This is a biscuit jointer
and this is a little biscuit. Now biscuits are certainly a step up from a simple butt joint. They're easy to make and they keep the boards aligned really nicely. But, they don't really bring a significant amount of strength into the mix. These little guys just
don't penetrate deep enough. Another option might be dowels. Two dowels will provide
a pretty strong joint. In fact, strong enough
for most applications. They're easy to set up
and they don't require anything more than a drill
bit and some patience. Although there are numerous
jigs on the market that will help you get consistent
placement of your dowels. Another good option
would be pocket screws. Any pocket screw fans out there? Yeah, I thought so. Now pocket screw technology's just a fancy way of saying "held together with screws". The screws are driven
at a very shallow angle and do a great job of
holding two pieces together. It's quick, it's easy, and if you don't mind screws it's a great option. But you'll have these screw holes to contend with in the back. Now they do make wood
plugs for these holes, but if I have to go
through that much trouble then I pretty much
negated any time savings. Now there is one last
alternative but I'm going to save that surprise
for a little bit later. I promise you though, it's
going to be "fescool". (banging drum cymbal) Before we go any further, let's get some terminology out of the way. Now this area here that runs parallel with the face of the board,
that's known as the cheek. The lip that surrounds
the actual tenon all the way around the board,
that's known as the shoulder. So what do we start with first? The mortise or the tenon? Personally I prefer to
cut my mortises first. The primary reason for
this is that the mortise is cut by something
that's a constant size. Either a router bit or a
hollow chisel mortising bit. And it can be tricky to make the necessary fine adjustments to
match that up to a tenon. Now the way a tenon is
made, on the other hand, allows for exact measurements
and slight adjustments. So it can really sneak
up on the measurement by cutting a little bit at
a time and test fitting. As a rule of thumb tenons
should be made about 1/2 the thickness of the board. So in the case of a
3/4 inch piece of wood, the tenon should be made
about 3/8 of an inch thick. The rule of thumb for
tenon length should be about four to five times
the thickness of the tenon. Again for a 3/4 inch thick work piece with a 3/8 inch tenon the
length would be between one and a half and one
and 7/8 inches long. This measurement also depends greatly on piece that we're gluing our tenon into. (banging sound) There are a number of
ways to make a mortise. This is pretty much the
way it used to be done. You can even use a drill
press and a forstner bit to hog out most of the material
and chisel away the rest. Well I could use my feet
to go down the road like Fred Flinstone in my car if
I wanted to, but sometimes you just need to take
advantage of technology. I find that when it comes to making a mortise and tenon joint, power tools are the fastest and most accurate way to go. That doesn't mean you shouldn't learn to do this process with hand tools. In fact, practicing some of these classic techniques is a great way to improve your manual dexterity and
confidence with hand tools. Most of you probably own a
router so this particular method is like to be the
most feasible option for you. Now I prefer to use an
up-spiral straight bit for creating my mortises. An up-spiral bit gives us
more efficient cut because it pushes the wood chips
up and out of the hole. The disadvantage is that the up-spiral bit may also tear out some of the wood fibers near the top of the mortise. But with a good, sharp bit
this usually isn't a problem. And even if there is a
little bit of tear out, it'll most likely be covered
by the shoulder of the tenon. Now you can use a down-spiral
bit if you have one, but they're better
suited for shallow holes. Now I actually need to
get a new up-spiral bit, so I'm going to use my
standard straight bit for now. Alright, let's set up for our mortise cut. Mark Spagnuolo: I begin by attaching an edge guide to the router base. Using double-stick tape,
I attach a second board to the mortise board and this
gives my rounter the extra support that it needs to
stay balanced and safe. I then clamp the boards between
two dogs on my workbench. After marking the location
of the mortise using a pencil and a straight
edge, I carefully set the straight bit right to the pencil line. After bringing the bit down
to the surface of the wood I use the built-in depth gauge and stop to set the plunge depth. With safety gear on and the dust extractor attached, it's time to start routing. (sawing sound) If the depth of the mortise is
greater than 3/4 of an inch, you may want to consider
making the cut in two passes. (sawing sound) When you're done you should have a nice, smooth walled mortise. You'll notice that I
didn't use stop blocks. I simply routed it to my lines. This makes the set up
go a little bit faster and if I go over the line
by 30 second of an inch it really isn't going to
make much of a difference. The joint's going to be just as stable. One other thing to note is
the fact that the mortise now has round edges. It means we'll either have to round over the edges of our tenon
later or we can square up the corners of the mortise
with a chisel right now. I prefer to round over the tenon. Call me lazy. Now I'd also like to mention
that you can certainly use your router table to make a mortise. But that usually requires slowly dropping the work piece onto a moving router bit, which is not exactly my
favorite thing to do . So if you can avoid it, you're
probably better off taking the tool to the wood rather
than the other way around. Ever wonder if you could
drill a square hole? Well with this machine you can. This is a hollow chisel
mortiser and you can find these for as little
as 200 dollars and probably even cheaper if you find a used one. It is a one-trick pony
but when that pony's trick is an essential woodworking
task like making mortises, it's really a good investment. Now this machine uses a
special boring bit that's housed inside of a four-sided chisel. Now as the bit hogs out
the bulk of the material, the chisel slices the hole
into a nice even square. Let's do a sample cut. Mark Spagnuolo: Setting
up the mortiser is easy. With a pair of gloves on I
insert the bit and the chisel keeping the chisel about
an 1/8 inch from the top. I then tighten the chisel
and the bit into place. Once the bit is secure I
raise the chisel to the top. This technique results
in the bit protruding just ahead of the chisel which results in a much more efficient cut. Placing a piece of scrap
against the fence, I rotate the chisel so that it's square
with the fence and the open end of the chisel faces either
to the left or to the right. This allows the wood
chips to exit the hole reducing friction and reducing heat. Using a mortiser is a lot
like using a drill press, but requires a lot more pressure. In fact, most people are quite
surprised by just how much force it takes to plunge
the chisel through the wood. If you've noticed by bulging biceps in previous episodes, now you know why. Seriously though, I actually
broke the ball joint on my mortiser once simply because I put way too much pressure on it. The culprit was a dull chisel. Word to the wise, keep
your chisel sharp using a cone-shaped diamond stone. Today I'm using alder
so it cuts like butter. (drilling sound) (banging wood) Mark Spagnuolo: Now
let's talk about tenons. Of course, just like with
the mortise, you could use a saw, some chisels,
and do this by hand. But for all the same reasons
I prefer power tool methods. My favorite methods all involve
the use of the table saw. Many of these cuts could be accomplished on the band saw, as well,
but I find that the table saw produces a smoother, more accurate cut. Mark Spagnuolo: The
fastest way that I know to make a tenon is to use a dado blade. This is a special stack
of blades that allow you to adjust to any size you need using these chippers
and some magnetic shins. Just make sure the arbor of your table saw is long enough to
accommodate the extra blades. Mark Spagnuolo: Switching
to a dado blade is simple. I remove the "zero clearance" insert and remove the splitter. Next I loosen the arbor nut using a piece of scrap to immobilize the blade. I assemble the dado blade with several chippers between the outer blades. The final width is about one inch. When tightening the arbor
nut I find that most people tighten way too much. I usually secure the blade with my fingers with a wrench on the nut and give the wrench a few taps with
a piece of scrap wood. As soon as the blade feels like it's going to slip out of your
hand, it's tight enough. Mark Spagnuolo: Now that we've got our dado blade installed notice that I have to remove the splitter in this case. Number one because the
insert that I use with my dado blade doesn't have
a space for my splitter. Secondly and more
importantly we need to pass this over the blade without
making a through-cut which would actually cause a major problem if we hit the splitter. After I mark the cut lines for my tenon, I like to set the fence up as a stop. Now this will allow me to
batch out as many tenons as I need and they'll
all be exactly the same. Now, there's a potential
safety issue here, though. If I use the fence as a stop
we could have a kickback when the work piece is over the blade and wedged between the
blade and the fence. That's when I use my little
handy auxiliary stop. It's shop made of three pieces of plywood and a couple of bolts. Now as long as the stop is
in position before the blade, the work piece will be
properly indexed for each cut without the danger of being wedged between the blade and the fence. Mark Spagnuolo: Using
my adjustable square, I mark the location of
the tenon's shoulder. I don't adjust the blade to the
final height on the first shot. I like to do a few test cuts
on the tip of the tenon. This way if I go too far
I still have the rest of the tenon to correct the error. After a quick test fit
we can see that we need to remove quite a bit more of material. (sawing sound) Test fit numbers two shows that the tenon's just a bit too big. I raise the blade just a little bit and take another cut on both sides. (sawing sound) Um, yeah, who's the man? With the fence adjusted and the blade set at the perfect height it's
time to cut the entire tenon. (sawing sound) I usually cut the tenon in
about four to five passes and then flip it over
and do the other side. (sawing sound) Using the same methods as before, cut the sides of the tenon, if necessary. And that, my friends, is
a tight fitting tenon. If the tenon fits too tight, a light touch with sandpaper usually does the trick. Although it doesn't do me any good now, a piece of scrap wood double-sticked taped to the miter fence will
help prevent tear out. Mark Spagnuolo: Now you could do this same operation with your standard blade. You just nibble away the
material a little bit at a time. This is OK if you have
one or two tenons to make, but if you got a whole
bunch it's a tedious process and the resulting cut's usually
a little bit less than ideal. Mark Spagnuolo: Now the
next method requires the use of a special jig known as a tenoning jig. You can pick up one of
these for about 60 bucks. The basic idea here is
to hold the work piece in a perfectly vertical
position while passing it safely over the blade. The resulting cut is
extremely smooth and accurate. And with the micro adjustments here, you can easily dial in the perfect cut. Time for an equipment check. Tenoning jig, check. Eye protection, check. Piece of wood, check. Spongebob pencil, check. That's how I roll. Mark Spagnuolo: After marking the location of the tenon shoulder, as
well as the tenon's profile on the end grain, I adjust
the fence to my pencil line. I then adjust the blade height just a hair under my other pencil line. I then cut a single curve on
both face sides of the board. I adjust the blade height one more time to cut the sides of the tenon. This time I'll take repeated passes until all of the material is removed. It's just easier to finalize
this dimension right now. Before using the tenoning
jig, I always make sure that the side and back stops are square. Using my curve cuts as a guide, I adjust the blade height in
preparation for the jig. While holding the work piece tight against the back and side surfaces I use the built-in clamp to
secure the work piece. I then use the jig's
micro adjustment feature to make sure that the blade is about a sixteenth of an inch
away from my pencil line. With the work piece secure
we can make our cuts. Be sure to wave at the
cut-off piece as it flies harmlessly past your right hip. After several rounds of
cutting and test fitting we now have the perfect tenon. Mark Spagnuolo: Now it
may seem like I'm adding steps by not aiming for my
pencil line on the first shot, but believe me, you're work
will be far more accurate if you use this relative
dimensioning method. In fact, I use relative
dimensioning on every project and for every type of joinery that I do. I'll go into more detail
on relative dimensioning in a future episode. Everything we've done
so far is a variation of what's known as an integral tenon. Where the tenon is actually
part of the work piece. An alternative to this method
is known as a loose tenon. It's a joinery method
where you create a mortise in both work pieces and
join them together with a separate piece of wood
that serves as our tenon. It's kind of like a really strong biscuit. It's a perfectly viable option
and it actually can be just as strong as a standard
mortise and tenon joint. One big advantage here is
the fact that the tenon stock is going to be milled from
one long piece of material. So it'll all be exactly
the same and you can make a bunch of tenons in one shot. And if you use a router
bit that's perfectly sized for a piece of plywood
you can cut all your tenon stock from sheets of ply. Can't get any easier than that? One big disadvantage
is that it's difficult to create mortises in the ends of very long pieces, like table aprons. I'm ready! Now keep in mind that if
your mortise has rounded ends like it will if you use
the router, you might need to round over the
corners of your tenon. You can do this with a chisel, a rasp, or even a sharp utility blade. Now sometimes you put the
tenon into the mortise and you see that there's
actually a little bit of a gap. You can't really get it to seat properly. So either your tenon's too long, which is an easy fix, you just trim it down. Or you might need to relieve
some of the material here on the shoulder between
the edge of the shoulder and where the shoulder meets the tenon. What you really want to
do is just with the chisel create a little bit of
a concave shape there so that really the only
thing touching the next work piece where the
mortise is this outside rim. It's not going to affect
the strength of the joint because all the strength is
in the long grain glue joint. So just make that concave and that should give you a perfect fit.
