This method to make a children's chair that fits together like a puzzle is remarkably simple, at least as furniture design projects go. This chair can be assembled and disassembled in less than a minute, making it a great piece for living with limited space or even taking it on trips. The puzzle aspect is also fun for kids, who can learn to set it up themselves.
Start with boards wide enough for the child to sit on comfortably and thick enough to support his weight safely.
Cut two lengths of board. The first should be about 3/4 of the child's height, and the second should be about 1/2 her height. For example, for a 4-foot tall child, you would want one 3-foot board and one 2-foot board.
Draw a line across the long board 1/3 of the way down and another line across the short board, 1/2 way down. In the example, these lines would be 1 foot along each board. The distance down each board should always be the same.
Cut a slot into each board along these lines. The slots should go just a bit more than halfway across each board, and each slot should be just wide enough to fit the other board into (This is important! Don't make them too wide).
Fit the boards together by turning so that the slots are facing in opposite directions, and slide the slots together until the boards make a lopsided "X."
Sand, decorate and finish the chair in any way you like.
The success of this project is based on the fact that the slots fit together, which is generally no problem if your boards are the same on the front and back, because you can turn one board over if necessary. Of course, if your boards have only one good side, you must be careful to cut one slot (either one) from the left side of the board, and the other slot from the right side of the other board.
The problem with making the slots too wide is that the chair won't fit together tightly and the boards will lay flat or almost flat instead of forming a usable chair. If in doubt, start with a very thin slot and gradually use a saw or sanding tool to widen it slowly, frequently testing with the other board for fit.