How to Cut a Box Joint Without a Dado Stack

Box joints (also called finger joints and comb joints, depending on where in the world you live) are a great way of making strong corners for boxes, drawers and the like, but they usually require the use of a dado head on the tablesaw. Smaller saws often cannot take a dado stack, but this jig enables me to cut perfect box joints, of ANY size, in inches or millimetres, WITHOUT A DADO, just using a standard Flat Top Grind rip blade.

It relies on nibbling out each socket by mounting the workpiece on a slider, moving it side-to-side by a very precise amount, to create a socket of the required size. By swapping in a different slider I can create a different size of joint.

Apart from setting the blade height, there is no setup at all, once the slider has been calibated for the particular blade, and that is a quick, one-time task. So although each socket requires multiple passes, the lack of complicated setup means that it's all quite a quick operation.

Tablesaw with a miter slot

Flat Top Grind Rip blade

Some 3/4" MDF or plywood, a few screws and a bit of steel plate

Cut a rectangle of MDF and attach a runner underneath do that it slides nicely in the miter slot. With your Flat Top Grind blade installed, make a short notch in the baseboard. This shows exactly where the blade is going to cut.

Over on the router table, rout a groove to take the vertical fence. Change the cutter for a V-groove cutter and rout another groove at right angles to it. This will take the alignment key for the front guard.

With the same v-cutter installed, rout a groove in the front guard block. Prepare a length of square stock for a diamond key so that the base and the guard slide sweetly together. Too fat and the guard will rock, too skinny and the guard will be loose. It must be a Goldilocks fit. The block should fit nicely over the saw line.

Over on the mortiser, make an adjustment slot. It doesn't have to be huge, inch-and-a-half long should be enough. Then, with the diamond key sitting between the two parts, mark though the slot with a pencil where you want the locking lever to be.

We need to install a nut at this point, but on the underside, not the top, so drill right through with the smallest drill you have, to show the exact same point on the underside. Then flip it all over and drill a shallow hole the same size as your nut spanner size, then right through at the clearance diameter of your stud. I'm using an M6 Bristol lever, so the shallow hole is 10mm (the spanner size for M6) and the through hole is 6.5mm (clearance size for M6). A nut is then pulled into the hole, creating a very secure fixing for the adjustable guard.

A fence is glued into the groove ensuring that it is truly vertical. A fixed stop is attached at each end, both of which have a steel face to prevent wear creating inaccuracies.

Screw a block of wood to the baseboard behind the fence, being careful to keep the screws away from the blade-line, so that the blade does not come out at the end of the cut. My thumbs are not far away, so this is important.

The slider carries the workpiece and determines the size of the joint. At each end of the slider is an adjustment screw, but rather than trying to screw just into the end-grain of the MDF, it's a better idea to insert a wooden cross-dowel and pilot and screw into that. It makes for a very secure fixing. The size of this is not critical at the moment, but as a general rule it should be about 20mm or 3/4" less than the distance between the steel faces.

With a shim filling the kerf of the jig, mark two points away from the blade, each one the finger unit away. Here I am marking 11 and 22mm. With a piece of scrap behand, to bring the slider forward of the fixed stops, nibble a shallow notch between the two marks. Prepare a length of stock to fill, cut off a short piece and glue it in place to become the indexing peg. Keep the rest for the next operation

With the shim in the kerf as before, insert the prepared stock between the indexing peg and the shim and push the slider as far to the left as possible. Remove the stock. Now push the slider to the left. If it moves, it means the screw is too far in, it needs to come out a bit. Keep trying until the stock is held in a Goldilocks fit when theadjustment screw is touching the steel face of the stop. The size of the finger is now set and we need to make the socket the same size.

With the right-hand screw well out, put the scrap we used moment ago over the indexing peg and nibble away, moving the slider left and right with each pass over the saw blade. If the prepared stock fits, great. If it doesn't, move the right-hand screw further in and nibble away a bit more. Keep adjusting the screw until the new socket fits nicely over the indexing peg.

If a different size of joint is required, simply make a different slider. I currently have 1/4", 5/16", 15mm and that well-know standard size, 11.4mm.

The jig is now ready to use.

Set the blade height to be a hair higher than the thickness of your workpiece, so that there is minimal cleaning up to doafter glue-up. You will have to remove the front guard to do this, so don't forget to put it back afterwards.

With the appropriate slider in the jig, move it hard over to the left. Locate the workpiece up against the indexing peg and adjust the guard to keep fingers and blade away from each other. Pass the jig over the saw blade, sliding between each pass so as to nibble out the first socket.

Lift the workpiece up and locate that first socket over the indexing peg and make the second socket. Continue until the workpiece is clear of the blade.

Flip the first side round, face for face, and locate the first socket over the indexing peg, so that the first pin fills the gap between the saw blade and the indexing peg completely. Put the second workpiece up against it and nibble away. Remove the first workpiece completely and move the second side up, over the indexing peg and nibble away as before.

The joint should go together perfectly. If it is too loose, move the right-hand screw out a bit to reduce the travel and try again. Conversely, if it is too tight, move the RH screw in a tad to increase the travel. The joint should not be tight - if it is tight when it is dry it will need a hammer when it is all wet with glue.

I very much hope that you build and use this jig. It produces perfect results without the need for a dado stack. The actual cutting of the sockets may not be quite as fast as using a dado stack, but it's not far behind, and given that there is virtually no setup time, it's actually quicker for short runs, such as two or three drawers.

I wish I'd built mine years ago.

Enjoy!