This project was built and designed by Brett from Brett’s Basement Woodshop. It’s a shop-built mortising jig that offers a budget-friendly alternative to high-end joinery tools like the Festool Domino.
Designed to work with a standard plunge router and guide bushing, this jig helps create strong, precise mortises for loose tenon joinery. It’s a smart solution for woodworkers looking to level up their joinery without a hefty investment.
Watch the full video and subscribe to Brett’s channel:
Why Use a Mortising Jig?
Loose tenon joinery is popular for its strength, alignment, and ease of use. This jig makes it easy to cut perfectly matched mortises for floating tenons using your existing router setup.
Instead of spending hundreds or thousands on a proprietary system, Brett’s jig uses shop-made parts and affordable hardware to achieve similar results. It’s accessible, customizable, and adaptable to various project needs.
Starting with the Platform
The jig begins with a sturdy platform made from laminated wood strips. Brett cuts the pieces oversized at first to allow for trimming after glue-up. This gives him the flexibility to square things up later and ensure the final dimensions are accurate.
A key component is the spacer block that defines the opening for the guide bushing. To get the perfect fit, Brett uses calipers to dial in the thickness before cutting the real piece. A snug fit here is critical for accuracy, so test cuts on scrap are highly recommended.
Once the thickness is right, the spacer is split into two parts. These are temporarily clamped and checked with the bushing before the full glue-up, helping avoid any surprises later.
Building a Durable Fence
Next, Brett builds a hardwood fence with dovetail slots to accept clamps and fixtures. He uses cherry for its durability and stability, which holds up well under repeated clamping and routing.
To reduce tear-out while routing, Brett cuts across the grain first, then follows with the longer slots along the grain. This order results in cleaner cuts and less chance of chipping at the edges.
After routing, the fence is trimmed to final size and double-checked for squareness. Precision here affects the performance of the jig, especially when aligning workpieces.
Aligning and Final Assembly
Before attaching the fence to the platform, Brett marks a centerline along the base. This line becomes the reference point for all mortise layouts going forward.
Countersink holes are added for the screws that will secure width stoppers. Once everything is aligned, the fence is attached to the platform and the jig begins to take its final shape.
Smart Adjustments and Fixes
During testing, Brett finds that the machine screws used for the width stoppers can spin freely if not anchored properly. He solves this by switching to T-nuts, which grip the underside and keep everything locked down.
Brett also suggests widening the platform if you plan to use the jig for sliding dovetails or extra-wide mortises. These small changes make the jig more versatile without adding much to the build time.
Setting Up the Jig for Use
To begin routing, the jig is clamped to your workpiece using dovetail clamps. The offset from the edge to the mortise centerline is typically set to half the material thickness—for example, 3/8″ for a 3/4″ board.
Width stoppers are attached to the top to define the length of the mortise. These can be adjusted as needed for different joinery setups, making the jig flexible for both small and large projects.
Routing Mortises with Clean Results
Brett uses a plunge router and low-profile guide bushing to make the mortises. Taking shallow passes is key here—not only does it reduce strain on the router, but it also keeps the cuts cleaner and extends the life of the bit.
Rather than trying to cut the full mortise in one go, Brett connects overlapping starter holes and slowly clears the waste. This technique creates accurate mortises with minimal cleanup needed afterward.
Using the Jig for Sliding Dovetails
Beyond loose tenons, the jig can also be set up for cutting sliding dovetail joints. This requires a bit of extra alignment, but the same principles apply: centerline referencing, depth control, and careful clamping.
Brett demonstrates this process in the video, showing how a single jig can perform multiple high-quality joinery functions with only slight adjustments.
An Excellent Alternative to High-Cost Tools
This mortising jig is a great example of building smarter, not more expensively. For a fraction of the cost of commercial systems, you can achieve pro-level joints using tools already in your shop.
Brett’s design is approachable, customizable, and easy to modify for your workflow. Whether you’re a hobbyist or a weekend pro, this is a useful addition to any woodworking setup.
Please support Brett by visiting his website: https://www.brettsbasementwoodshop.com/.