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Sure Lock Miter Gauge
With fence and flip stop.


Benchtop Router Table With Porter Cable 690 Router


Delta Miter Jig
Rigid, precise tool.


Delta 10" 1 1/2HP Contractor Table Saw



Jeff Greef Woodworking

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Making Finger Joints

Finger joints are also called "box joints," probably because they are so ideal for joining the sides of a small wooden container. Setting up to make them is fast and simple, though adjusting the setup to get the result you want can take time with a bit of trial and error. Small alterations in the setup have large effects on the fit of joints, particularly on wider joints. But by using test pieces you can make these adjustments easily and make a lot of snug, attractive joints.

Resources for making Finger Joints

Miter Gauges |  Table Saws |  Router Tables

You can make this joint on a table saw or a router table. In either case the jig itself and the procedures remain the same. You need to have some means of pushing the jig across the blade or bit, such as a miter gauge or a cutoff box. Choose a ripping blade when setting up on the table saw if you have one because it leaves a square end on the cut. Cross-cut and combination blades will leave a small V, which is slightly visible on the finished joint. You might find that this small V doesn't bother you. A dado could be used for a wider finger; in this case adjust the tongue thickness and distance from the blade according. On a router table the width of your fingers will be determined by the diameter of straight flute bit you use for the cuts between fingers.

Photo 1- The jig consists of two long boards and a small tongue. One board is attached to a miter gauge, the other is clamped to the first. The tongue is fitted into a slot in the clamped board.

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For router tables, click here.

The jig has a small tongue alongside the path of the blade set to allow progressive cuts in the part, each cut being referred to the last by placing the last cut over the tongue (see photos 1 and 2). Begin making the jig by making this tongue. Make the thickness of the tongue the same dimension as the saw kerf so that each cut will fit on the tongue with no looseness. Any looseness will cause a variation in spacing between cuts, causing a poorly fitting or non-fitting joint.

Make the jig from two pieces of stock approximately 3/4 x 4 x 20". Screw the first to your mitre fence, and clamp the second to the first. The second has the tongue, and is clamped onto its mate so that it can be adjusted back and forth to align carefully the distance between the tongue and blade. This is the critical adjustment that determines the fit of the joints. When first setting up the jig, set the distance between the tongue and the blade by measuring with a rule, and set the distance equal to the thickness of the cut made by the blade. Make the adjustment by loosening the C-clamps on the jig just slightly so that a small rap with a hammer on the end of the piece will move it just a hair. After making such an adjustment, retighten the clamps. Once you have a blade and tongue set-up adjusted as close as possible by measure, make the final adjustment of the distance from the tongue to the blade by making test joints on scrap.

Photo 2- Use the tongue as the reference point for making each of the cuts in the joints. After each cut, lift the part off the tongue and place the last cut over the tongue. Now you're set up for the next cut.

To make one side of a joint, first place the piece vertically in the jig butted up against the tongue, and make a cut. Pull the jig back across the blade, lift the piece over the tongue and slide the first cut onto the tongue. Again push, retract, and laterally advance the piece, and continue the process until you have gone the width of the part (see photo 2). Note that the joint starts with a tongue at the point where you began, thus the mating piece must have a cut in this place in order for the edges of the parts to line up. To achieve this, insert a spacer between the tongue and blade for the first cut on the mating piece as in photo 3. Make the spacer equal in thickness to the distance from the blade to the tongue. Since the spacer and tongue are both the same thickness, make them both when you make the tongue.

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Photo 3- On matching parts you need to make a cut on the very edge of the part for the first cut. Do so with a spacer placed between the tongue and part as shown.

When you have your first two test pieces you will quickly see whether the tongue to blade distance is correct by the fit of the two parts. When the distance is too great the fingers are too fat to fit the grooves, when too little they are loose. Scribe a line across the tops of the two main jig pieces, then adjust the distance from tongue to blade watching this scribe to see how much you have moved the clamped jig piece. A little goes a long way.

When you are running your pieces through the progressive cuts for each joint, be careful to always hold each part with the same pressure from your hands and with your hands in the same position. This is because even if the tongue has a tight fit in the cut, you can vary the position of the cut slightly by pushing one way or the other. If you happen to push one way on all the cuts for one piece, and then push the other way for all the cuts on the mating piece, the combined difference can offset the fingers enough to prevent them from fitting, as in photo 4. But with a tight fit at the tongue and consistent holding the result will be quite uniform and well-fitting.

Photo 4- This mis-aligned joint was caused by pushing the lighter colored board to one side during all of its cuts. The combined effect is to offset the spacing enough that the joint doesn't fit.

While making cuts always watch the blade as you push the wood into it. This is the best safeguard to prevent yourself from pushing your fingers into the blade. Don't look off to the side while you push the jig across the blade.

When you make joints that have more than 8 or 10 tongues, it's best to check the fit of the joints while you are in the process of cutting them. You may find that, half way through cutting the mating piece, the fit is a bit loose or tight. Adjust for this by applying pressure one way or the other while the part is loaded in the jig during the next 5 or 6 cuts, to make the parts match.

Tearout can be a problem with brittle or highly figured woods. Placing a cover sheet behind the piece will help. If it is still a problem, tearout can be turned into the box by loading the pieces in the jig such that the outside face is always toward the blade. In order to do so it is necessary to place the tongue on the opposite side of the blade when doing mating parts. Thus you cut half the fingers with the tongue on one side, then reset the tongue to the other side of the blade, and check the fit with test pieces, then cut the other half of the parts.


Resources for making Finger Joints

Miter Gauges |  Table Saws |  Router Tables


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