In woodworking, the mortise and tenon joint reigns supreme as one of the strongest joints available. When it comes to cutting precise mortises, you can’t go wrong with a trusty plunge router. The key is to make sure those mortises are straight, clean, and parallel to the workpiece faces. To accomplish these objectives, an adjustable router mortising jig becomes indispensable.
A router mortising jig simplifies the process by enabling you to set stops, securely attach and adjust the workpiece, and consistently and repeatably achieve perfect mortises. In this article, I will provide step-by-step instructions on how to make your own mortise jig. The jig is portable and allows for easy attachment to any workbench using clamps, making it an ideal solution for those with limited workshop space.
For this project, I will be mainly using plywood and MDF as primary materials. These types of wooden boards are favored for their strength, durability, and resistance to bending under pressure. However, if you prefer, hardwood such as oak or beech can also be used as an alternative material.
Let’s get started!
How to Make a Router Mortising Jig Video
If you want to see how it is done, watch the video below for a step-by-step guide on how to make a router mortise jig.
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Table of Contents
- Mortising Jig Video
- The Material you will need
- General Questions
- Benefits of a Router Mortising Jig
- Advantages of Mortise and Tenon Joint
- Mortise Router Bit
- How to Make a Router Mortising Jig
- Step 1: Make the Clamping Fence
- Step 2: Make the Mortising Jig Body
- Step 3: Make the Router Base Plateau
- Step 4: Assemble the Mortising Jig
- How to Use a Router Mortising Jig
- Woodworking Jigs Used
*Safety is your responsibility. Make sure you know what you’re doing and take all necessary safety precautions while working with power tools. Safety comes first!
Material you will need to make a Router Mortise Jig
Mortise Jig
Fence – Plywood – 265 mm x 130 mm x 24 mm – https://amzn.to/3TPULp2
HDF Strips for t-slot matrix
Body – Ply – 265 mm x 100 mm x 24 mm
Square Supports – Ply 2x – 80 mm x 50 mm x 12 mm
Base – Ply – 350 mm x 100 mm x 9 mm
Base – Ply – 305 mm x 225 mm x 5 mm
Ply strips for the router table
Other:
Wood Glue – https://amzn.to/48ltKhJ
Epoxy – https://amzn.to/3tJ5R4L
Sandpaper Sheets – https://amzn.to/41OMx2p
Painters Tape
Wood Screws, Square Nuts, T-nuts – https://amzn.to/41PodgQ
DIY T-track Bolts
DIY Star Knobs
Tools:
Trim Router – https://amzn.to/3HbQcOg
Corded Hand Drill / Drill Press – https://amzn.to/3NSA3Bo
Circular Saw – https://amzn.to/4aMD0xg
Table Saw – https://amzn.to/47mWiGf
Cordless Hand Drill – https://amzn.to/3HqLEnH
One Hand Clamps – https://amzn.to/48jGxkZ
Spring Clamps – https://amzn.to/41Nuh9D
Mini Hand Clamps – https://amzn.to/3RJwNJK
T-track Clamps – https://amzn.to/3tEKaCW
Machinist Square / Speed Square
Narex Chisels – https://amzn.to/3tHNJrT
Orbital Sander – https://amzn.to/48G9cjL
Check all the Tools I Use
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Benefits of a Router Mortising Jig
A router mortising jig is a game-changer when it comes to cutting mortises accurately and efficiently. These are the key benefits of using a router mortising jig:
- Repeatability: A router mortising jig ensures consistent and repeatable mortises, allowing you to achieve uniform results throughout your woodworking projects. Each mortise you create using this simple jig will match the exact specifications.
- Accuracy: The jig allows you to achieve unparalleled accuracy in your mortises. Its design, combined with its adjustable features and guide systems, ensures that each cut is made in the right place.
- Easy Setup: Setting up the jig is very simple. The jig consists of a simple base and adjustable components that allow you to position and secure your workpiece with ease.
- Versatility: The jig offers versatility in creating mortises of various sizes and shapes. Whether you need to make square, rectangular, or even curved mortises, the jig’s adjustability and guide systems can accommodate different routing requirements.
Advantages of Mortise and Tenon Joint
The mortise and tenon joint is a woodworking technique that offers numerous advantages for sturdy and reliable connections.
- Superior Strength: The mortise and tenon joint provides exceptional strength and durability, making it ideal for load-bearing structures such as furniture and frames. This joint ensures long-lasting and secure connections.
- Enhanced Stability: With its interlocking design, the joint offers excellent stability, minimizing the risk of wobbling or shifting over time. This stability is crucial for maintaining the structural integrity of the project.
- Increased Load Capacity: Thanks to its robust construction, the joint can bear heavy loads without compromising its integrity. This advantage makes it well-suited for applications that require supporting substantial weight, such as tables or cabinets
Versatile Design: The joint is versatile and adaptable, allowing for various configurations. Whether it’s a through mortise, blind mortise, or wedged tenon, you can customize the joint to suit your design needs.
Mortise Router Bit
When it comes to cutting mortises with precision and efficiency, choosing the right router bit is crucial. There are two popular options for mortising – the straight-edge router bit and the spiral up-cut router bit. Let’s take a look at their advantages, use, and purpose.
1. Straight Edge Router Bit
- Advantage: The straight-edge router bit is a go-to choice for clean and accurate mortises. Its straight cutting edge ensures precise and straight-sided cuts, resulting in tight-fitting joints.
- Use and Purpose: This router bit is commonly used for creating traditional square or rectangular mortises. It excels in applications where a clean and precise edge is required, such as furniture joinery and cabinetry.
2. Spiral Upcut Router Bit
- Advantage: The spiral up-cut router bit is renowned for its excellent chip evacuation properties. Its spiral design effectively removes debris and prevents clogging, resulting in smoother cuts and reduced heat buildup.
- Use and Purpose: This router bit is particularly useful when working with materials that tend to produce a lot of chips or shavings, such as softwoods and composites. It is also well-suited for plunge routing operations and creating deep mortises.
Let's start building!
Making a router jig for mortises involves making the adjustable base for the router and the clamping fence (upright assembly) for workpiece attachment.
Securing the workpiece in the router mortising jig is quick and straightforward, taking just a few seconds. The jig’s back fence features a convenient t-slot matrix, allowing you to use homemade t-track clamps or shop track clamps for added versatility.
With the ability to accommodate various thicknesses and widths of workpieces, this jig enables you to cut mortises in different orientations—horizontally, vertically, or at any desired angle. It even handles more complex mortises, such as double mortises, parallel mortises, and mortises in round stock. This makes it an excellent project for those with limited workspace, offering a space-saving solution without compromising functionality.
Router Mortise Jig properties:
- Material: Baltic birch plywood, HDF, Wooden Knobs
- Total dimensions: 350mm x 225mm x 125mm
- Maximum mortise dimension: 100mm
How to Make a Router Mortising Jig
Step 1: Make the Clamping Fence
To begin constructing the router mortise jig, the first step is crafting the back clamping fence. This fence acts as a sturdy support for the workpieces and is designed with a t-slot matrix, allowing easy attachment of clamps. It is positioned perpendicular to the router base.
To create the clamping fence, start by cutting two plywood boards measuring 13×26.5cm. You can use either a table saw or a circular saw with a straight-edge guide. Next, glue the boards together. Draw the t-slot matrix pattern on the surface of the fence. To cut the slots, use a router dado guide, which will help you achieve precise and uniform results.
Additionally, cut thin strips of HDF and glue them into the slots, forming a t-track matrix for attaching clamps.
TIP: Use an orbital sander to round the edges and flatten the surface.
Step 2: Make the Mortising Jig Body
To ensure the clamping fence remains perpendicular to the router’s jig base, it’s crucial to create a supporting body where the adjustable router base will be installed.
Begin by applying glue to the clamping fence and firmly attaching it to a plywood board measuring 265mm x 100mm x 24mm. Use corner clamps or a machinist square to ensure the boards are perpendicular to each other. For added stability and a secure connection, insert screws into the joints and reinforce the structure with plywood squares.
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Step 3: Make the Router Base Plateau
Now let’s make the router base plateau. It is constructed using HDF and attached on top of the jig body. HDF is an intentional choice for the router table due to its strength, straightness, flatness, and smooth surface, which allows for easy sliding of the router.
To begin, cut a square hole in the base. You can use a jigsaw, but for a more precise cut, you can use a router square template guide. Next, glue plywood strips on top of the HDF desk, using the router’s base as a reference to ensure a perfect fit.
To incorporate the side stop blocks, drill holes on each side of the base. Flip the base upside down and carve either a hexagon or square shape to accommodate a nut. Apply epoxy to securely glue the nuts in place, providing a permanent attachment.
Lastly, cut two slots through the base, allowing for attachment to the jig body and providing the flexibility to adjust it as needed.
Step 4: Assemble the Mortising Jig
When assembling the various components of the mortise jig, make sure the fence and router plateau are perpendicular to each other, while the jig body and plateau remain parallel.
Begin by securely gluing two plywood strips to the bottom of the plateau, ensuring a snug fit around the jig body. This step enables smooth back-and-forth sliding of the router table during operation.
Next, drill two corresponding holes in the jig body that align with the router table slots. Flip the body upside down and insert two t-nuts from the bottom, providing a secure anchoring point for the router table.
Apply glue to the bottom of the square supports, and carefully attach the body to a base strip. This setup allows for easy attachment of the mortise jig to the workbench using clamps. Lastly, add the side stops and mount the router table onto the body using wooden knobs.
This is what the finished router mortising jig looks like
How to Use a Router Mortising Jig
When using a router mortising jig, it’s important to follow proper techniques to ensure accurate and clean cuts. Here’s a step-by-step guide:
- Securely place the router mortising jig on a workbench and use clamps to tightly fasten it in position.
- Position the workpiece against the fence of the jig, and utilize t-track bolts and hold-down clamps to firmly secure it in place. Ensure that the center of the mortise aligns with the center mark on the router table.
- Install the appropriate router bit into the plunge router and place it onto the router table.
- Adjust the router plateau as necessary to locate the center of the mortise, and once positioned, tighten the wooden knobs to secure it in place.
- Set the side stop blocks to establish the desired depth and width of the mortise, ensuring consistent and repeatable cuts.
Begin the cutting process by making multiple passes, gradually removing around 5mm of material with each pass. This technique prevents burn marks, minimizes pressure on the router bit, and ensures sharp and clean cuts.
With the router mortising jig properly set and aligned, you can effortlessly create precise and repeatable mortises. This versatile tool also allows for cutting at various angles, including horizontal, vertical, and even into miters, expanding its applications in woodworking projects.
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How to Build a Mortising Jig for a Router
Woodworking Jigs I used to build it:
During the construction of the mortise jig, I utilized various woodworking jigs that facilitated the process. While not all of them are essential (almost none of them), they made the work much easier. However, there are multiple alternatives that can be employed.
