Building a Wooden Jig to Create Precise Mortises Using a Vertical Router (by Capitan Farloc)

In the world of woodworking, precision is key. When it comes to creating mortises in wood, using a vertical router can make the job much more efficient and accurate. However, to achieve the best results, it's essential to have a jig that helps replicate cuts exactly where you want them.
In this article, I'll walk you through how I designed and built this wooden guide—an indispensable companion for anyone looking to create neat and precise mortises using a vertical router.
With this homemade jig, you’ll be able to craft Tenon and Mortise joints with greater accuracy, unlocking a world of creative possibilities and excellent results.

Why Use a Jig

Let me start by saying that this project came about because I embarked on building a support table for my circular saw—a brilliant project showcased by Mariobrossh in his article: Building a Table to Support the Circular Saw (by Mariobrossh).
The first challenge I hit was: How do I make mortises for the joints that are all identical in both position and size?
That’s when I decided to create a jig to make things easier by addressing these key needs:

1. Expanding the support surface for the vertical router to prevent it from wobbling and making crooked cuts.
2. Adding a stop to ensure the mortises are always the same distance from the top of the batten.
3. Incorporating stops that allow me to fix the length of the mortises.

After giving it some thought, this is what I came up with... But let’s take it step by step!

Marking the Mortise Outline on the Wood

The first step I took was to mark on the beam I’m using for the workbench (well, actually on some scrap pieces to test things out first) the position and dimensions of the mortise I want to create.
This outline will help me set up the stops and guides for the router and the jig, so I can register the mortise’s position and replicate it identically on all the other parts of the bench I’m building.

Using a Wooden Strip and a Stop to Create the Jig

So, I grabbed a wooden strip (I had some leftovers about 2 cm thick and 5 cm wide) to make my jig. This strip's purpose is to expand the support surface, and onto it, I screwed another wooden rectangle to act as a stop. This way, I can ensure that the pieces where I need to cut the mortises will always be positioned on the jig in exactly the same way.

Positioning the Jig

The jig should be positioned by placing the beam against the wooden piece used as the stop, and, of course, aligning the edge of the jig with the surface of the beam. In this photo, I’ve added another strip of wood (optional) on the opposite side of the beam to further increase the support surface, making the router base’s positioning even more stable.

Adjusting the Router's Side Guide

At this stage, I can adjust the side guide of the vertical router to get the correct distance of the bit from the edge of the beam.
One thing I had to pay attention to is that the beams (made of unplaned spruce to save on costs) sometimes have slightly different dimensions—one or two millimetres of variation. This can create annoying steps in the joints. To avoid these steps being visible, I always positioned the jig on the side of the beam that will be "on display" when assembling the workbench. This way, I can ensure the pieces align on the visible side of the bench, hiding any differences in the widths of the pieces on the side that's out of sight.

Using the Router's Side Guide

By using the router's side guide, I can be confident that the mortises are made at the correct distance from the edge. Meanwhile, the width of the mortise is fixed and determined by the bit’s diameter (14 mm in this case), so that part doesn’t worry me.

Building the Stops for the Start and End of the Mortise

Now, all that’s left is to set the start and end points for the router bit’s cut, and to do this, I needed two stops to attach to the jig.
So, I took two small wooden blocks, the same width as the strip I used for the jig, along with two long screws, matching nuts, and washers.

Using a Metal Profile for the Stops

Next, I used a piece of metal profile about a couple of millimetres thick and marked four sections slightly longer than the width of the wooden blocks I’m using as stops.
I also marked the points where I’ll drill holes to attach these sections to the blocks.

Marking Drill Points

I marked the drill points with a centre punch. It’s always a good practice—even when using a drill press—to use a steel punch to mark the position where the hole needs to be made. This acts as a guide for the drill bit, helping it stay precisely on the marked spot.

Then, using the drill press, I made the holes—first with a 3mm bit and then, for the holes where the larger screws go, I followed up with an 8mm bit.

Using a hacksaw, I cut the four pieces along the lines I had marked on the metal profile.

Assembling the Stop Clamps

After drilling the 8mm holes in the wooden blocks, I attached the metal pieces as shown in the photo. In the smaller holes, I used wood screws to prevent the metal parts from rotating. In the larger holes, I inserted the long screw along with the nut and washers, creating a kind of clamp. By tightening the nut, the clamp can grip and lock securely into position on the jig.

To enhance the grip of the clamps (and improve the rigidity of the fastening), I added rubber pads to the protruding parts of the metal pieces that act as the jaws of the clamp.

Positioning the Stop Clamps on the Jig

the final step is to position the router with the bit aligned to the edge of the mortise. Then, in this position, attach the first clamp to the wood of the jig, so it serves as a stop by coming into contact with the guide, as shown by the arrows in the photo.

The same process is repeated on the other side with the second clamp to establish the endpoint stop for the mortise.

Testing the Jig

At last, I can turn on the router and, after positioning the jig, start creating my mortises.
After running a few tests, I can say I’m satisfied—the mortises seem to have turned out quite well.

Here’s the moment of truth: testing the dry assembly of the trial pieces.

I hope it has been interesting and helpful to someone. Thank you to everyone who stumbled upon this site and took the time to read this article—have a great day!

P.S. If you have any questions, suggestions, or simply want to let us know you enjoyed the article, feel free to write a message on the Forum where this article originated by following this link.

Guida (o dima) per fare le mortase con la fresatrice verticale

Thank you
Luciano (Capitan Farloc)