How to Make Perfect Finger Joints with a Table Saw Jig
Finger joints are one of the strongest and most attractive ways to join the corners of a woodworking project. The evenly spaced, interlocking pins create a large amount of glue surface, making the joint an excellent choice for boxes, drawers, cabinets, and other projects that need durable corner connections.
Also known as box joints, finger joints have a distinctive appearance that highlights the joinery rather than hiding it.
Best of all, you don't need an expensive commercial jig or complicated equipment to make them.
With a table saw, dado blade, and a simple shop-made finger joint jig, you can cut matching pins and notches that fit together accurately.
The key is building a little adjustability into the jig. This makes it easy to fine-tune the fit without spending a lot of time changing your setup.
Here's how to build the jig, cut the joints, and assemble them for strong, square corners.
What Are Finger Joints?
A finger joint is a woodworking joint made from a series of evenly spaced rectangular pins and notches cut into the ends of two boards.
The pins on one board fit into the notches on the mating board, creating an interlocking corner.
When glued together, the joint provides a large amount of long-grain glue surface.
This makes finger joints particularly useful for projects that need strong, durable corners.
They're also an attractive design feature.
The exposed end grain creates a repeating pattern that looks especially good on boxes, drawers, and small cabinets.
For example, the finger joints used on Woodsmith's Machinist's Chest provide both strength and a traditional appearance.
Finger Joints vs. Box Joints
The terms finger joint and box joint are often used interchangeably to describe this type of interlocking corner joint.
In furniture and cabinetmaking, both terms commonly refer to the square pins and notches shown here.
Unlike dovetails, finger joints have straight sides rather than angled tails and pins.
This makes them easier to cut with a table saw and dado blade.
Build a Simple Table Saw Finger Joint Jig
The secret to cutting accurate finger joints is a jig that controls the spacing of every cut.
For this method, the jig attaches to your table saw's miter gauge.
It uses two fences and a small hardwood indexing key.
The key fits into each notch as it's cut, positioning the workpiece for the next cut.
This creates evenly spaced pins across the end of the board.
The Rear Fence
The rear fence attaches directly to the miter gauge with screws.
Its main purpose is to support the adjustable front fence.
Drill slightly oversized clearance holes for the screws that connect the two fences.
These holes allow the front fence to shift slightly from side to side.
That small amount of movement is what makes it possible to fine-tune the fit of the joints.
The Front Fence and Indexing Key
The front fence is the working part of the jig.
It holds a hardwood indexing key that controls the spacing between the cuts.
The front fence also supports the workpiece during cutting, helping reduce tearout along the back edge.
I prefer Baltic birch plywood for the front fence because it's flat, stable, and easy to work with.
The rear fence can be made from a straight, flat piece of hardwood.
Since the jig is simple to build, it's often easier to make a new front fence for a different finger-joint size rather than trying to adapt one fence to every project.
Step 1: Set Up the Dado Blade
Finger joints can be cut with a table saw and a properly sized dado blade.
The width of the dado determines the width of the notches and matching pins.
For the Machinist's Chest, the finger joints use 1/4"-wide pins in 1/2"-thick stock.
Start by installing a dado blade set to the required width.
Make sure the blade is compatible with your table saw and follow the manufacturer's instructions for installing and operating the dado set.
Set the Cutting Depth
The depth of the notches should match the thickness of the mating workpiece.
For this technique, begin with the dado blade set just below the thickness of the stock, then verify the final fit with test cuts.
The goal is to create a joint that seats fully and can be sanded flush after assembly.
Use test pieces to determine the final blade height before cutting the project parts.
Step 2: Install the Indexing Key
The indexing key is what makes the finger joint jig work.
It establishes the distance between each notch, allowing you to cut a repeating pattern without measuring every cut.
Cut a Slot in the Front Fence
With the dado blade installed, hold the front fence in position against the rear fence.
Don't attach it permanently yet.
Make a cut through the front fence to create a slot for the indexing key.
The slot will match the width of the dado blade.
Make the Hardwood Key
Cut a small piece of hardwood to fit the slot.
The key should fit snugly without requiring excessive force.
If it's too loose, the workpiece may shift during cutting.
If it's too tight, the notches will be difficult to position over the key.
Make the key slightly longer than necessary.
Then trim off a short piece to use as a spacer during setup.
Position the Key
The distance between the indexing key and the dado blade determines the width of the pins.
For equal-width pins and notches, this spacing needs to match the width of the dado cut.
Use the hardwood spacer to establish that distance.
Position the front fence so the spacer fits between the key and the outside cutting edge of the dado blade.
Once everything is aligned, attach the front fence to the rear fence with screws.
Leave the screws just loose enough to allow minor adjustments during test fitting.
Woodsmith Tip: Accurate spacing is more important than making the jig complicated. A carefully fitted indexing key and a small amount of fence adjustment are all you need to produce consistent finger joints.
Step 3: Make Test Cuts and Check the Fit
Before cutting the actual project parts, make a pair of test joints.
Use scrap pieces that match the thickness and width of your project stock.
This allows you to check the spacing, cutting depth, and overall fit without risking your finished workpieces.
Cut the First Set of Fingers
Start with the edge of the first test piece positioned against the indexing key.
Hold the workpiece firmly against the jig's front fence and make the first cut.
After completing the cut, move the workpiece sideways so the new notch fits over the indexing key.
Make the next cut.
Repeat the process until you've cut the full series of notches.
The indexing key automatically establishes the spacing for each cut.
Cut the Matching Workpiece
The second board needs an offset pattern so its pins fit into the notches of the first board.
Use the first completed workpiece to establish this offset.
Position its first pin over the indexing key, then butt the mating workpiece against it.
Make the first cut in the second workpiece.
After that, continue indexing each notch over the key until the joint is complete.
This creates a matching set of interlocking fingers.
Check the Joint Fit
Bring the two test pieces together.
A properly fitted finger joint should slide together with firm hand pressure or a light tap from a mallet.
You shouldn't need to force the pieces together.
If the joint is too tight, the pins may split or the parts may be difficult to assemble before the glue begins to set.
If the joint is too loose, the glue surfaces won't make consistent contact.
The goal is a snug, predictable fit.
Step 4: Fine-Tune the Finger Joint Jig
Even a carefully built jig may need a small adjustment before it produces the fit you want.
That's why the front fence is attached through oversized screw holes.
A slight movement of the fence changes the spacing between the cuts.
If the Joint Is Too Tight
Loosen the screws holding the front fence.
Move the fence slightly so the distance between the indexing key and dado blade increases.
This increases the width of the pins' mating spaces relative to the pins.
Retighten the screws and make another test joint.
If the Joint Is Too Loose
Move the front fence slightly in the opposite direction, reducing the spacing between the key and blade.
This produces a tighter fit.
Make small adjustments.
A tiny change in the key-to-blade spacing can make a noticeable difference across several pins.
Continue testing until the joint fits properly.
Woodsmith Tip: Adjust the jig using fresh test pieces rather than trying to correct an existing joint. Once the notches are cut, their spacing can't be changed without removing additional material.
Step 5: Cut Finger Joints in the Project Parts
Once the jig produces a good fit, you're ready to cut the actual workpieces.
The cutting process is the same as it was for the test pieces, but there are a few details worth watching.
Keep the Workpiece Against the Fence
Hold each board firmly against the front fence throughout the cut.
For larger parts, particularly wide or tall pieces made from 3/4"-thick stock, use a suitable clamp to secure the workpiece to the jig.
This improves control and helps keep the cuts consistent.
Always keep your hands clear of the dado blade and use the jig only with a suitable table saw setup.
Keep the End Flat on the Table
The end of the workpiece needs to remain flat against the table saw surface during every cut.
If the board lifts, the notch may be too shallow.
That can prevent the joint from seating fully during assembly.
Take a moment to check the workpiece position before making each pass.
Mark the Reference Edges
Finger joints are easier to cut consistently when you establish a reference edge on every workpiece.
Mark the boards so you know which edge should be positioned against the indexing key for the first cut.
This helps ensure that the finger patterns line up correctly when the project is assembled.
Check the Fit as You Work
After completing each matching pair of joints, test the fit.
This confirms that the jig hasn't shifted out of position.
A quick check can prevent a small setup problem from affecting every part of the project.
Once the setup is dialed in, the actual cutting goes quickly.
Step 6: Glue and Assemble the Finger Joints
One advantage of properly cut finger joints is that they're easy to align during assembly.
The interlocking pins help keep the corners square as the pieces come together.
However, the large number of mating surfaces means you need to work efficiently during glue-up.
Prepare Before Applying Glue
Dry-assemble the project first.
Make sure all the joints seat fully and the parts fit together without excessive force.
Have your clamps, mallet, glue, and any assembly spacers ready before opening the glue bottle.
For larger projects, a glue with a longer open time can make assembly less stressful.
Apply Glue to the Mating Surfaces
Use a small brush to spread a thin, even coat of woodworking glue across the mating surfaces.
Make sure the sides of the pins and notches receive adequate coverage.
Avoid applying so much glue that it prevents the joints from seating or creates excessive squeezeout.
Once the glue is applied, bring the parts together promptly.
Use a mallet and protective block if needed to seat the joints.
Clamp the Assembly Square
Apply clamps to pull the joints together.
Check that the corners remain square as you tighten the clamps.
For a box or cabinet, temporary plywood spacers can help support the sides and maintain alignment.
Clean Up the Joints
Once the glue has cured, remove the clamps and inspect the corners.
If the pins extend slightly beyond the mating surfaces, trim or sand them flush.
Remove any remaining glue residue before applying a finish.
The finished joint should have clean, evenly spaced fingers and tight-fitting shoulders.
Common Finger Joint Problems and Solutions
Even with a simple jig, a few setup issues can affect the finished joints.
Finger Joints Are Too Tight
Possible cause: The indexing key is positioned too close to the dado blade, or the dado width and key size don't match.
Solution: Adjust the front fence slightly and make another test cut.
Finger Joints Are Too Loose
Possible cause: The distance between the indexing key and dado blade is too large.
Solution: Reduce the spacing slightly and test the fit again.
The Pins Don't Line Up
Possible cause: The mating workpieces weren't offset correctly, or the reference edges were inconsistent.
Solution: Mark the reference edges and use the first completed workpiece to establish the offset for the mating board.
The Joint Doesn't Seat Fully
Possible cause: The dado blade was set too low, or the workpiece lifted during cutting.
Solution: Check the blade height and keep the workpiece flat against the table during every cut.
Tearout Along the Back Edge
Possible cause: The workpiece wasn't fully supported behind the cut.
Solution: Use a clean, close-fitting front fence to support the wood fibers as the dado blade exits the cut.
Strong, Attractive Joinery with a Simple Jig
Finger joints are a practical choice whenever you need strong corners and want the joinery to become part of the project's appearance.
With a dado blade and a shop-made table saw jig, you can cut matching pins accurately and efficiently.
The adjustable front fence makes it easy to dial in the fit, while the indexing key keeps the spacing consistent from one cut to the next.
Once you've built the jig and worked through a few test joints, you'll find plenty of opportunities to use finger joints in boxes, drawers, cabinets, and other woodworking projects.
And because the jig is inexpensive and easy to make, it's a useful addition to almost any woodworking shop.
Build a Classic Machinist's Chest
Show off your woodworking skills with this traditional machinist's chest. Strong, attractive finger joints give the case lasting durability and a distinctive appearance. Get the complete woodworking plans and build a practical storage chest that's as impressive as the tools it holds.
GET THE MACHINIST'S CHEST PLANS → Put Your Finger Joint Skills to Work
