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How to Mark Layout for Mortise & Tenon Joint in Woodworking

Learn how to make mortise and tenon joints from Makeville Studio in this Howcast woodworking video, part 1 of a 2-part series.


The mortise and tenon joint is a classic woodworking joint for joining rails and styles and frame-style construction of furniture. So, this has been used in tables, chairs, you name it. And it's a very strong joint and you just make two pieces. There's a tenon, which is basically a stub that's sticking out of one piece. And then, you've got a mortise which is a hollowed-out rectangle in the other piece. And these two made up to create a tight joint that gets glued and a very strong joint.

So, how do you make this joint? There's a couple different methods. We're going to be using a table saw and the drill press for the mortise. But the first step in making any joinery is doing the layout on your actual pieces of wood. Let's put our model aside. We're going to make a new joinery on these pieces. Now, the design of the mortise and tenon follows some basic rules about proportions to the stock that you're using.

For instance, tenons. Generally, you don't want them to be any smaller or larger than one-third of the width of the stock that they're cut out of. So, for example, in this piece of wood, we've got a one and a half-inch wide piece. So, we're going to make our tenons a half-inch wide. In the other direction, you can be a little more flexible. You can make them longer, if they need to be. They can be the whole length, in fact, of this piece of wood. They can be the whole two inches.

We're going to make a fully-shouldered, though just because that becomes a little bit nicer and easier to hide the scenes around in the pieces when they go together. We're using a marking gauge, mortise and gauge. These have different names. And, what we've got here is a movable face that will index up against the side of the wood that we're going to be marking that provides a reference surface against which, these two pins will scribe lines that outline the sides of the tenon.

So, these pins are adjustable. This one can move just by pulling and pushing on that control, there. And we know we want our tenon to be one half-inch wide. So, I'm just going to set this to one half-inch using my ruler. There's a half-inch. There we go. And now, we're going to want to also set the position of this face where we want it. Now, we're obviously going to want that tenon in the middle of the piece of wood. So, if this one and half inches wide, we've got half-inch, half-inch, half-inch. I'm going to need to be a half-inch in. So, I'll measure a half-inch from this face to that first pin, as well. Okay.

There's a lot of eyeballing involved here. And one of the things, whenever you eyeball something in woodworking, you always want to test it first. It's good to have scrap wood for this. You can test out your settings. And what's happening is those pins are scribing lines, while I have this face pressed up against the side of the wood. And that's what's keeping them in the right place. Now, I'm going to check my work. Like I said, when you eyeball things, sometimes, they're a little off. So, I'm checking if I'm a half-inch from the end and I'm checking if there's actually a half-inch between those scribe lines.

Okay, so the rest of the marks for the tenon. What we want to do for any woodworking joinery is always mark all the way around. So, there's going to be a set of lines scribing around the top of this wood, around the other sides and also, at the depth that we want to go. And that's actually the next decision we have to make about this joint. We know the width, the length is somewhat arbitrary. The depth of it, though, is not arbitrary. We have to stay within the confines of what we have available for this connecting tube, right? So, here's the tenon going into the mortise.

We only have this thickness of wood right here to house this tenon. We don't want to go all the way to the edge. This is somewhat arbitrary, but I'm just going to say, let's go, instead of a full two-inches, let's go one and a half inches deep. That's most of the way through. The farther you go, the bigger the tenon you can make, the more glue area, the stronger the joint will be. So, it really does depend a little bit on what you're making. If you're making something that's going to have a lot of racking and force on it, for example, a chair, you're going to want to make that tenon as big as possible.

So, one and half inches will have to be measured on here, as well. And that's going to be the line of the shoulder, all the way around. This is similar to the mortise and gauge, it's called a wheel marking gauge. And it also has a face that you reference against. Instead of pins, it has a wheel that scribes a line. It's a sharp-edged wheel. There we go. It just locks into place with this brass knob.

Now, I can take the marking gauge and I'm going to just scratch this line. You can see I'm pressing in, pressing down on that black wheel, pressing forward with this brass face and dragging this towards me. It takes a little practice, but once you get it, it's very fast. And I've now got a line all the way around. Now, if you didn't have this or this tool, this could be really challenging. If you've ever tried to mark something and carry it around four faces you usually end up at a different place due to the thickness of the pencil and just your eyeball error. So, a tool like this sort of takes away all that error and it's very handy.

Now you want to avoid doing what I'm doing right now which is scratching more than once. Often, you will make a different line on the second time just because your hand moves. We made a half-inch boundary for this. We're going to do a half-inch boundary on the ends, as well. So, fully scribe out these lines. Down to the sides, around the top. Once I pencil these in, we will have the complete outline that we need to cut this.

All right, so the tenon is marked out. The mortise is going to be laid out in a similar way. We know it's centered in the wood just like the tenon is, right? So, we can use the marking gauge to scratch those lines. Because we're using the marking gauge with the pin set in exactly the same place, it's going to align perfectly. That's relatable.

Now, the location of this is sort of arbitrary. Depends on what you're doing. Sometimes, you'll want to join your piece of wood right flush with the top. Sometimes, you'll want to set below for a different reason. So, for the purpose of our exercise here, I'm just going to mark it arbitrarily down a little bit here. And we had a one-inch tall mortise. I'm just going to measure that with pencil, here and mark it. So, that's our location for the mortise.

Okay, now we can take these over to the tools and get them fit.

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