Making Mortises Using a Plunge Router

Here’s a way to make mortises using a plunge router. You will need a fence on you plunge router. I’ve already got one attached in 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 quarter 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.

I’ve got a simpler technique. I’m going to 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 going to make any cuts with it. If you look at this, with that v-bit in there, what that shows me is a very distinct center point for the center of my collet. In other words, now I can very easily calculate where the center f the mortise will be.

In this case, I’ve got one and half inch wide legs. I want the mortise centered on the leg, so the distance to the center of mortise is three quarters 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 layouts, that’s going to come back out of there. My quarter inch bit has got a half inch shank on it, so I’m also going to change my collet. This one, we’re actually going to cut wood with, so we want to be sure that we secure this one in the router.

Let’s get this leg 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 going to 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. I’m going to start up 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 them.

Our mortise depth is one half inch. We can now use the turret and stop system on the router in order to make sure that we get that depth correct. Here’s how this is going to work, I’m going to touch the router down. At that point, that bit is kissing the top of the wood. What I need to do is make sure that the distance from the bottom of the stop rod to top of the turret is the depth of my mortise. Instead of trying to poke a ruler in their and measure, I’m going to use a piece of this bar stock. This piece right here is one half inch by one half inch. I’m going to put that on top of the turret, loosen up my stop rod, push that down until it touches and lock my stop rod.

Now, without having to do any measuring at all, I know that’s a perfect half inch. It means my router bits going to go in a perfect half inch. 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 going to pivot my stop rod over here. In the first place, I’m going to touch down this up a little bit higher. In other words, I’m only going to cut about half of that mortise in the first pass.

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 under the leg then I've slid the router bit to the extreme right under the mortise, trace the base of the router on the leg and that’s because it’s a whole a 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 the router, we do end up with around ended mortise because of the router bit itself. 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. 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.