How do you make a table saw box joint jig?

A table saw box joint jig is an indispensable tool for woodworkers looking to create strong and precise box joints. Box joints (also known as finger joints) interlock lumber pieces together at right angles, allowing for sturdy joinery on boxes, drawers, and more. With a dedicated jig, you can produce clean and accurate box joints quickly and easily on your table saw.

In this comprehensive guide, we’ll walk through everything you need to know to build your own table saw box joint jig from scratch. We’ll cover how box joints work, the benefits of using a jig, essential design considerations, a step-by-step building tutorial, tips for achieving a perfect fit, and more. Let’s get started!

What is a Box Joint?

A box joint is a classic woodworking joint used to securely interlock two pieces of lumber (usually at 90 degree angles) to construct boxes, drawers, and other boxy assemblies. The hallmark of the box joint is its distinctive interlocking rectangular “fingers” that mesh into one another.

To create a basic box joint, matching rectangular tabs or “fingers” are cut into the ends of each workpiece, allowing them to tightly interlock at the joint. The fingers on one workpiece fit into the spaces between the fingers on the mating workpiece, creating a strong mechanical joint.

The benefit of the box joint is that when assembled properly, the interlocking fingers prevent the joined components from pulling apart in any direction. By distributing force along the length of the joint, box joints are inherently stronger than simple butt joints secured with nails, staples or glue alone.

Advantages of Box Joints

Box joints offer several key advantages over other joinery options:

Increased gluing surface area – More surface area for glues and finishes to adhere to.
Excellent tensile strength – The interlocking fingers resist force in all directions.

Precise alignment – Fingers align pieces accurately at 90 degree angles.
Attractive aesthetic – The interlocking fingers have a pleasing visual appeal.

Thanks to these benefits, box joints are commonly used by woodworkers worldwide for all kinds of applications from jewelry boxes to cabinetry.

Why Use a Box Joint Jig?

Creating box joints by hand can be an extremely laborious and imprecise process. Cutting the individual fingers to exactly equal widths without error is virtually impossible. A dedicated box joint jig solves these problems by guaranteeing flawless results with much less effort.

Here are the main advantages of using a jig:

Precision – Jigs ensure all fingers are cut to equal, optimal width.

Repeatability – Once setup, a jig will cut perfect joints every time.
Support – Jigs properly support the workpiece for accuracy.
Speed – No complex layout or test cuts needed, just flip a switch.

Safety – Table saw jigs allow safer cuts versus freehand.

For hobbyists looking to make just a few box joints, a jig may seem excessive. But for any woodworker doing production work, a table saw box joint jig is an indispensable time and quality saver.

Table Saw Box Joint Jig Design

While shop-made jigs come in many shapes and sizes, the basic design concept is straightforward:

The jig rides along the table saw fence to ensure straight cuts.
It positions the workpiece at the exact blade width to cut each finger.
It flips the block after each cut to index the next finger.

Essentially, the jig moves the stock sideways and flips it between blade passes to create the interlocking fingers. With the critical dimensions configured correctly, the jig does all the hard work of aligning, spacing, and cutting the joint.

Let’s look closer at the key components and design considerations for building a table saw box joint jig from scratch:

Key Components

Sled – The main jig body that holds the workpiece and slides along the fence.

Toggle clamp – Secures the workpiece to the sled during cuts.
Indexing pin – Flips workpiece to the next finger spacing.
Arm / linkage – Connects pin to a cam or handle to actuate flipping.

Stop block – References workpiece position for first cut.

The sled needs to be sized to provide ample workpiece support on the table for safety and accuracy. Hardwood is ideal for durability, but many jigs also incorporate plywood and other sheet goods. The clamping method can vary, but a sturdy toggle clamp provides quick, strong hold down. A pivoting arm linked to the index pin does the work of flipping the workpiece between cuts.

Critical Dimensions

For the jig to function properly, several key dimensions need careful configuration:

Pin Width – Pin width determines finger width. Make it slightly thicker than saw kerf.
Pin Spacing – Gap between pins sets finger spacing. Typically 0.25” to 0.5” range.

Pin Offset – Half the pin spacing, to flip workpiece between cuts.
Sled Travel – Limits sled movement to prevent overcutting fingers.

The specific dimensions will vary depending on your design and the saw kerf of your blade. But in general, the pin width should match the blade kerf, the spacing should allow for strong fingers that don’t break easily, and the travel should permit cutting only the width of each finger.

Building a Table Saw Box Joint Jig

Now that we’ve covered the key concepts, let’s walk through the full process of building a table saw box joint jig step-by-step.

For this build, we’ll use plywood for the main sled, hardwood for the cam and structural parts, and off-the-shelf hardware for the clamp and pivots. You can modify dimensions or materials as needed.

Cutting List

Here are the pieces required to build the jig:

2	3/4″ plywood sled sides, 5″ x 24″
1	3/4″ plywood sled front/back, 5″ x 12″
1	3/4″ hardwood sled base, 3-1/2″ x 24″
2	Hardwood cam, 3/4″ x 5″ x 5″
1	Hardwood indexing pin, 3/4″ x 1-1/2″ x 5″
1	Hardwood cam axle, 1/2″ x 5″
1	Hardwood cam arm, 1/2″ x 3″ x 6″

You’ll also need a toggle clamp, two 1/4″ dowel pins, two fender washers, one 1/4″ wing nut, and various screws and glue.

Step 1 – Cut the Plywood Pieces

Cut the plywood sled sides, front, back, and base pieces to size according to the cutting list. The two 24” sides mount vertically, while the 12” front and back span horizontally.

Step 2 – Drill Holes in the Sled Sides

Drill a series of 1/4″ holes in the sled sides to allow adjusting the cam axle position. Space the holes every 1” centered vertically. Make sure to drill both sides identically.

Step 3 – Assemble Sled Frame

Assemble the four sled pieces into a box frame using wood glue and brad nails. The plywood base should sit 3-1/2” up from the bottom to align with typical table saw height.

Step 4 – Make Indexing Pin

Cut the 5” indexing pin piece to finished size. Rip a 3/4″ strip to make the pin. Round over the edges with sandpaper.

Step 5 – Make Cam Pieces

Cut the cam axle and arm to length according to the cutting list. Also make two identical 5” square cam pieces. The specific cam profile is not critical.

Step 6 – Install Cam Axle

Install the cam axle through the aligned holes on the sled sides. Position it vertically centered at about 8” back from the front. Secure with washers and wing nut.

Step 7 – Attach Cam Arm

Screw the cam arm piece to the center of the cam axle at 90 degrees. Make sure it pivots freely.

Step 8 – Attach Cams

Screw one cam piece to each end of the cam axle, aligning the arm midway between them. The cams should rotate together, pushed by the arm.

Step 9 – Attach Index Pin

Screw the index pin to the sled top, placing it parallel and nearly touching the right sled side when viewed from the front. It should pivot freely.

Step 10 – Position Clamp

Mount the toggle clamp to the left side of the sled top. Position it to secure workpieces for cutting while avoiding the flipping action of the pin.

Step 11 – Test Mechanism

Test the cam and pin mechanism by rotating it through full travel in both directions. If needed, adjust positions for smooth actuation avoiding binding.

Step 12 – Attach Stop Block

Finally, screw a stop block to the sled base against the right sled side. This positions workpieces identically for the first cut when abutted against it.

The main jig mechanics are now complete! You’re ready to fine tune it to dial in perfect joints.

Tuning and Using Your Box Joint Jig

With the jig built, there are just a few remaining steps to optimize it for flawless performance:

Setting Pin Width

Ideally the pin should be slightly thicker than the kerf of your saw blade. For example, with a standard 1/8” kerf blade, make the pin 3/16” wide. This spacing ensures smooth travel cutting only one finger at a time.

Configuring Pin Offset

The gap between the pin and side determines the amount the jig “flips” the workpiece for each cut. A good starting point is usually 1/4″ but test cuts can optimize.

Limiting Sled Travel

Use a stop screw against the jig side opposite the pin side to limit lateral sled travel. This prevents overcutting fingers. Position it to allow just enough travel to cut each finger but no further.

Cutting Test Joints

With the critical dimensions dialed in, cut test joints in scrap material. Check for tight fit without gaps. Make small adjustments and additional test cuts until satisfied with the joint quality.

Once the jig is properly tuned, you’re ready to start putting it to work! Just follow these steps each time you need to make box joints:

Set blade height to just over workpiece thickness.

Set fence to align jig for first cut.
Place workpiece against stop block and secure in jig.
Push jig through cut, cutting all fingers on one end.

Flip workpiece using cam handle.
Cut all fingers on opposite end.
Repeat cam flip and cut for all remaining fingers.

It takes practice to get fast with the process, but you’ll be cranking out perfect box joints in no time. And best of all, every joint will be precisely aligned and gap-free thanks to your jig’s flawless accuracy.

Tips for Perfect Box Joints

Follow these tips and tricks to get the most out of your table saw box joint jig:

Use wax or lubricant to reduce friction when sliding the jig.

Cut fingers in multiple light passes for clean edge cuts.
Match your plywood to the final thickness for flush joints.
Use a sacrificial zero clearance insert to avoid tearout.

Always feed jig slowly and keep fingers secure in jig.
Use a stop block to reference identical workpiece positions.

It’s also extremely helpful to label matching workpieces (like drawer sides) to streamline glue-up assembly later.

If you take the time to tune the jig carefully and refine your process, you’ll be knocking out gallery-worthy box joints with ease. Part of the beauty of box joints is the flawless precision they allow when made using an accurate jig.

Conclusion

While simple in concept, a table saw box joint jig opens up endless opportunities for elegant wood joinery that would be nearly impossible by hand. With a shop-built jig properly tuned to your saw, you can quickly cut box joints for drawers, cabinets, boxes, picture frames, and anything else your projects call for.

We’ve covered everything from basic joint mechanics to complete jig building steps to usage tips and tricks. The beauty of the box joint hasn’t changed much in centuries, but the right jig makes executing it on a table saw pure joy. Clamp up some box joints today and appreciate both the enduring appeal of the joint itself and the modern precision of your handy jig. Your woodworking will be the better for it.