We developed this simple gear construction to be an occasional substitute for commercial plastic gears. Straightforward for older primary children with some building experience.

Each gear wheel is constructed using two 38mm card discs (1.5 inches) with 10mm wooden blocks as spacers. A tyre of corrugated paper is glued around the edges. Corrugations vary - try to get paper with 6mm corrugations, thats about 4 corrugations per inch.

The CROWN WHEEL has a half matchstick inserted into each corrugation. This is the fiddly bit! This action is helped by rounding the matchstick ends with fine glasspaper. Loose ones can be glued!

The frame in the illustrated model is built from 10mm square timber. The bearings are lengths of plastic drinking straw, wrapped with masking tape. The small disc acts as a stopper, keeping the gears meshed when the crown wheel is beneath the pinion.

This unit works any way up and could be just the job for any children building a model mill. The pinion will be turned by the sails or the waterwheel and, in turn, the crown wheel will rotate the 'millstone'.

Next month's project will be a more sophisticated gear system based on a Leonardo da Vinci design.
It will, however, use the same building system shown above.
Keep Watching!