Observation chair

Saturday, July 01, 2006

A simple cost effective way to build stable furniture without the need of specialized wood worker's skills.

Cheap and Stable

This chair costs less than 15 Euros. The seated position is adjustable in a range from 30 cm until 80 cmand it can be build using regular home worker tools. A jigsaw and a router can be handy but are not really necessary. The use of a power sander or a portable planer can speed up things enormously.

The roof batten system

The cheapest wood available is the so called roof batten which is a blunt plank of common spruce typically 2,5 x 4 x 200 cm. I just layered multiple battens in order to build an amazingly strong construction.

The first layer of planks is layed out on the table, wood-glue is applied and the second layer is nailed on top of the first layer. The same procedure is used for the third layer:

The workpiece is cramped and the glue can dry out over night:

All surfaces are smoothed using router and power sander. Note the filled nail holes of the last layer:

This T-joint looks nice and is very strong:

The height of the small leg is 40 cm, the height of the big leg is 1 meter. The width of both legs is 46 cm.

The seat

I used the same layered batten system. The seat counts 10 layers. Each batten is positioned in a way that the direction of the growth rings alternate, doing so will avoid distortion caused by shrinkage movement.

Layer 5 and layer 6 consist of 2 battens each. The smallest are cut under an angle, all other are rougly planed down to about 3 cm thickness using a power planer:

The surface and all edges are smoothed using jigsaw, router and sander:

The teeth

I copied the angle for the teeth from my child's chair, that angle measures about 20 degrees. I wanted one teeth per 4 cm resulting in 15 levels. It turned out that I don't really need 15 levels during observation, 10 levels would have been okay.

Of course, I could have used any saw but I used a Japanese hand saw to cut the teeth. Japanese saws cut on the pull stroke, so the blades are much thinner. As a result, they cut a narrow kerf with no tearing of the grain. Unfortunately, Japanese saws are expensive.