How to cut box joints by hand

How to make a box joint using hand tools, part 1

Sometimes we call them finger joints, but I guess those are other type of wood joints and that the actual name of what I will make in this post is box joints. And here in Spain we sometimes also call them finger joints o uniones tipo dedos o uniones de dedos. Maybe the right name in Spanish should be “uniones de lazos rectos”. Well, I have to say that recently I was given a (well deserved) little bit of a telling-off, explaining to me that box joints in Spanish are called uniones de lazos rectos. The truth is that I have seen these woodworking joints with different names, but definitely the names that I like the most and that make it clear what kind of wooden joints we are talking about are “box joints” in English and “uniones de lazos rectos” in Spanish. And that’s what we’re going to see in this post, how to cut a box joint. Or at least how I cut them. And I admit I am not very skilled making these kind of woodworking joints.

To cut a box joint in two boards with the same width and the same thickness I start by marking the thickness of one of the boards on the end of the face of the other board, and on both sides (1). Now I have to mark the dimensions of the pins I will cut on the line (2), distributing the pins in such a way that they are symmetrical with respect to the center of the line (the center of the board). With the help of the square I draw the perpendicular in the end of the board (3).

Mark the size of the pins of the box joint

And I continue the line on the end perpendicularly to the corner (4), and trace the perpendiculars to the end on the other face of the board (5). Just to avoid mistakes when cutting this box joint, I have to mark which are the pins I want to keep and which are the sockets I want to cut (6). And all this with using a pencil as sharp as possible.

How to cut the pins of the box joint

Ahora, con la uña sobre la línea coloco la sierra pegada a la uña, quedando así la sierra justo a la derecha de la línea y en el hueco que quiero cortar (7). Y voy a cortar con la sierra inclinada casi hasta llegar a la línea horizontal que me marca la altura de los dientes(8). Después corto el otro extremo del hueco dejando la sierra a la izquierda de la línea, realizando ambos cortes en este lado de la tabla para todos los huecos. Y giro la tabla en la mordaza de banco casera (9). Con la tabla girada vuelvo a cortar sobre los mismos cortes que ya hice, pero esta vez con la sierra en horizontal, asegurándome de que no llego a cortar la línea horizontal que marca la altura de los dientes (10). Ahora con una sierra de marquetería corto unos milímetros por encima de la línea horizontal, eliminando así la mayor parte de la madera de los huecos que quiero dejar (11 y 12).

With the chisel, mark the base of the sockets.

To finish working on this board I just need to clean the sockets between the pins. I lay the board flat on my workbench, and with a chisel I start marking on one face of the board right on the line that tells where the base of the sockets is.

Cut three-fourths of the board thickness.

Y ahora con la cara plana del formón hacia la tabla, y con este perfectamente vertical, voy a clavar el formón hasta la mitad o algo más del grueso de la tabla. Empiezo en un extremo y voy avanzando sobre la línea solapando un corte con el anterior. Con el formón bien afilado y la ayuda de la maza de madera, el formón entra en la madera sin mayor problema.

Mark and finish cutting the sockets with the chisel.

I rotate the board and mark the line between the pins on the other side. This time, when I drive the chisel into the wood, I reach the cut I had made from the other side of the board. This way I can remove the wood I had left at the base of the sockets when using the fret saw. Due to lack of expertise and perhaps because the wood is very dry, or maybe the wood is not the most suitable for cutting these box joints, sometimes there are some “holes” in the center of the base of the sockets caused when the wood breaks. It is not something that worries me too much, since those “holes” will be hidden when making the box joint with the other board.

Use the chisel to clean the base of the sockets.

To finish cleaning the holes, with the flat side of the chisel always resting on the base of the sockets, I carefully pivot and move the cutting edge sideways and move it forward, cutting the protruding wood little by little.

Use the chisel to adjust the sides

And on the sides of the sockets, with the flat part of the chisel against the corresponding pin, and the chisel perfectly vertical, I will retouch the cut to leave it clean and as vertical as possible.

Draw pins on the other board to make box joint.

Now I can use the pins and sockets I cut on this board to draw the sockets and pins on the other board with which I want to make the box joint. But that will be in the next woodworking post in this blog. Or else, in the following video I show the complete process with all the steps I follow to make this wood joint.

-> Ir a la segunda parte.

Scroll to Top