(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.