Making Mortises with a Plunge Router

Here's a way to make mortises using a plunge router. You will need a fence on your plunge router, so I've already got one attached to my router here. The layout is complete on this set of legs, so let's have a look at how I'll set this all up. This is the bit that we'll be using for the mortise. This is a 1/4-inch straight bit.

But what I found is that it's difficult to do the layout with this bit. In other words, to calculate the distance from the edge of this cutter to the fence can be kind of hard to do. So I've got a simpler technique. I'm gonna start out by putting this bit, a V-bit, in the router, and all you have to do is make it finger tight. We're not gonna make any cuts with it.

Now if you look at this with that V-bit in there, what that shows me is a very, very distinct center point for the center of my collet. In other words, now I can very easily calculate where the center of the mortise will be. In this case, I've got 1 1/2 inch wide legs. I want the mortise centered on the leg, so the distance to the center of the mortise is 3/4 of an inch. So now, with the V-cutter, I can quite easily measure from the fence to the center of that bit and lock my fence in place.

Like I said, we only use the V-bit for layout. So now that's gonna come back out of there. My 1/4-inch bit has got a 1/2-inch shank on it, so I'm also gonna change my collet. Now this one we're actually gonna cut wood with so we want to be sure that we secure this one in the router. Now let's get these legs set up.

What I found is that, if I simply rest the router on one leg, it's very tippy. So what I want to do, I want to have more than one leg to stand on. What I'm gonna do is pair two of these legs up. That broadens the base. It gives the router a bigger surface to rest on so it doesn't rock so much.

So I'm gonna start out by clamping these legs together, and then I want to clamp the legs to the bench so they're not trying to run away while I'm trying to work on 'em. Our mortise depth is 1/2 inch, so we can now use the turret and stop system on the router in order to make sure that we get that depth correct. So here's how this is gonna work. I'm gonna touch the router down. At that point, that bit is kissing the top of the wood.

Now, what I need to do is make sure that the distance from the bottom of the stop rod to the top of the turret is the depth of my mortise. And instead of trying to poke a ruler in there and measure, I'm gonna use a piece of this bar stock. This piece right here is 1/2 inch by 1/2 inch. So I'm gonna put that on top of the turret, loosen up my stop rod, push that down until it touches, lock my stop rod. So now, without having to do any measuring at all, I know that's a perfect 1/2 inch, which means my router bit's gonna go in a perfect 1/2 inch.

Now, if you pay attention to your turret here, it's got a couple different positions on it. We don't want to try to cut this entire depth of mortise all in one pass. So for my first pass, I'm gonna pivot my stop rod over here, and the first place I'm gonna touch down is up a little bit higher. In other words, I'm only gonna cut about half of that mortise in the first pass. So in order to know where the router starts and stops, I'll bring the bit here to the left end of the mortise and then simply trace the router base onto the leg.

Then I've slid the router bit to the extreme right end of the mortise, traced the base of the router on the leg. That's because it's a whole lot easier to see these pencil lines than it is to lean over and look down inside there to determine the starting and stopping points of the mortise. At this point, we can plug the router in and make this cut. One thing to notice is that, when you make mortises with a router, we do end up with a round ended mortise because of the router bit itself. So when we make a tenon to fit this joint, it's much easier to round the shoulders on the tenon than it is to try to square the internal parts here on the mortise.

So when you fit your tenon, you'll need to round that off. But this is a pretty simple way to make mortises using a plunge router.