This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
The base of the developing machine consists of a wood tray with sloping ends and high sides, which is placed at the center and provides bearings for the wheel axle. The dimensions given in the sketch are for making a machine to develop a film about 29 in. long. The disk, or wheel, is cut from a board, 7/8 in. thick, and the attached cross-pieces are cut from 1/4-in. dowels to make them 2 1/2 in. long. These are placed about 1 in. apart on the circumference of the disk.
An axle, fastened solidly in the wheel and adjusted in the bearings, is kept from slipping sideways by bushings made of a spool. A crank is attached to one end of the axle. Hot paraffin is applied to the inside of the tank part, to make it liquid-tight. Two pins or hooks are attached to one of the crosspieces to catch into the film end. If the wheel is the correct size, the same pins can be used for fastening the other end of the film.
The film is first attached to the wheel; then, while turning slowly, the developer is poured into the tray. Keep on turning the wheel until full development is obtained, then pour out the liquid and turn in fresh, clear water, and turn the wheel to wash out the developer. Remove the flim and place it in the hypo bath. - Contributed by Raymond M. Bealer, Baltimore, Md.
Ill: The Entire Length of Film is Placed on the Wheel Where It is Run through the Developer