You don't need an elaborate jig or a dedicated mortising machine to cut accurate mortises with a plunge router. This simple router mortising jig uses a basic bench-mounted design to hold the workpiece securely while providing a stable platform to guide the router.
The jig is easy to build from common shop materials and can be adjusted for different mortise lengths. It can also hold angled workpieces, making it a versatile option for furniture parts that can be awkward to mortise using other methods.
If you're looking for a straightforward way to cut occasional mortise-and-tenon joints with a plunge router, this jig is a good place to start.
A Simple Approach to Router-Cut Mortises
A plunge router is a great tool for cutting mortises. The challenge is guiding the router accurately while keeping it stable over the workpiece.
This jig solves both problems without requiring a complicated mechanism.
The workpiece clamps vertically against an upright support. Above it, a wide platform supports the router and provides an adjustable opening that guides the cut.
With the workpiece securely held and the router supported on a flat surface, you can concentrate on making smooth, controlled passes.
How This Basic Router Mortising Jig Works
The design has three main components: a two-piece router platform, vertical workpiece support, and bench-mounting bracket.
The workpiece clamps against the upright directly below the router. A guide bushing in the router base follows the opening in the platform, while adjustable stops limit the router's travel.
Move the stops and you can change the length of the mortise.
It's a simple arrangement, but that's really the appeal. There are no complicated sliding tables or adjustment mechanisms to build.
Build the Two-Piece Router Platform
The heart of the jig is the two-piece platform at the top.
This creates a wide, flat surface for the router base, which is especially helpful when mortising narrow workpieces such as table legs, rails, and frame components.
Instead of trying to balance the router directly on the edge of a workpiece, the router remains supported by the jig throughout the cut.
Add Adjustable Stops for Mortise Length
The opening in the platform incorporates adjustable stops that determine how far the router can travel.
The stops are held in place by hardboard strips that fit into grooves in the two platform pieces. Threaded knobs lock everything down once the mortise length is set.
Move the stops closer together for a shorter mortise or farther apart for a longer one.
This provides a simple mechanical way to control the ends of the mortise rather than relying solely on layout lines.
Match the Stops to Your Guide Bushing
A guide bushing installed in the router base follows the opening and stops.
The version shown here uses a 3⁄4" guide bushing, but the jig can be adapted for other sizes by changing the stops.
Remember that the guide bushing controls the router's travel, while the diameter of the router bit determines the width of the mortise.
Add the Upright Workpiece Support
The vertical section of the jig provides a flat surface for holding the workpiece directly below the router.
Slots in the upright allow you to position clamps wherever they're needed. This makes the jig adaptable to project parts of different sizes.
It also gives you a convenient place to attach a simple positioning stop when you need to make the same mortise in several workpieces.
Use a Stop for Repeat Mortises
For repeated mortises, clamp a guide or stop to the upright after positioning the first workpiece.
The remaining parts can then be placed against the same stop.
This isn't as fast or sophisticated as a dedicated precision mortising jig, but for a handful of matching joints, it's an easy way to improve consistency without adding much complexity to the jig.
Clamp the Mortising Jig to Your Workbench
A lower bracket provides a convenient surface for securing the jig to your workbench with clamps.
This does two things.
First, it keeps the jig stable while routing. Second, it raises the workpiece to a comfortable height, making it easier to see your layout lines and control the plunge router.
Make sure the jig is firmly secured before you begin routing.
The basic jig can be assembled with glue and screws, making it an approachable shop project that doesn't require much specialized hardware.
Set Up the Workpiece for Mortising
Mark the location of the mortise clearly on the workpiece before placing it in the jig.
Position the workpiece against the upright so the layout falls directly below the router opening. Then clamp it securely.
Adjust the platform stops to establish the required mortise length and lock them in place.
For a one-off mortise, your layout lines may be all you need to position the workpiece. For several identical parts, add a positioning stop to the upright after setting up the first one.
Use a Spiral Upcut Bit for Mortising
I like to use a spiral upcut router bit for this type of mortising.
The spiral cutting action produces a clean surface while helping pull chips up and out of the mortise. That's particularly useful as the cut becomes deeper.
Choose a bit diameter that matches the desired width of your mortise.
Before routing, also make sure the guide bushing is properly installed and centered around the bit.
Cut the Mortise in Several Passes
Don't try to plunge immediately to the full depth of a deep mortise.
Instead, make a series of progressively deeper cuts.
Make the First Shallow Pass
Position the plunge router on the platform with the guide bushing inside the opening.
Start the router and plunge the bit into the workpiece. Move the router smoothly between the two stops to establish the mortise.
Then retract the bit.
Increase the Depth
Adjust the plunge depth and make another pass over the same area.
Continue working down in stages until the mortise reaches its final depth.
Multiple shallow passes are easier on the router and bit and give you better control over the cut.
Use the Jig for Angled Mortises
One of the more useful features of this simple design is its ability to handle angled workpieces.
Because the workpiece clamps against the upright independently of the router platform, you can position a furniture component at an angle while the router remains supported on the flat surface above it.
This can make the jig useful for mortising angled legs, rails, braces, and other furniture components that don't fit conveniently into a more conventional mortising setup.
A securely clamped workpiece is especially important when using the jig this way.
When Is This Simple Mortising Jig a Good Choice?
This jig makes the most sense for a woodworker who wants an inexpensive and uncomplicated way to cut mortises with a plunge router.
It's easy to build, uses common materials and hardware, and can be adjusted for different mortise lengths and workpiece shapes.
It's also a useful solution if you only cut mortises occasionally and don't need the speed or fine adjustment offered by a more sophisticated mortising setup.
For a few mortises in a table, cabinet, frame, or other furniture project, this basic jig may be all you need.
Want More Precision and Repeatability?
If you make a lot of mortise-and-tenon joints, there's an advantage to stepping up to a more sophisticated jig.
Woodsmith's Precision Router Mortising Jig adds easier workpiece positioning, adjustable stops, a toggle clamp, and more precise control over the location of the mortise. Once it's dialed in, the setup makes it much faster to cut a series of identical mortises.
It's the same jig Chris demonstrates in the Woodsmith Shop router joinery video.
GET THE PLANS: Router Mortising Jig from WoodsmithPlans.com
The basic jig remains a great shop-built solution when simplicity is the goal. But if you're regularly building furniture with multiple mortise-and-tenon joints, the precision version offers a worthwhile upgrade in speed, adjustment, and repeatability.
