Wooden Screws. Single piece screws cut out of a block of wood are easy to make and very efficient. The propeller is laid out on a square or rectangular strip of wood (according to the pitch), cut to the required length. A pocket knife or a wood rasp is used to rough the wood down to the shape shown at B. It is then finished down to the form shown at C. After rubbing with sand-paper a coat of varnish is applied and allowed to dry. The varnish is then rubbed down to a smooth surface.
FIG. 33. Methods of fastening propellers to shaft.
Fig. 33 shows a very good method of mounting the propeller on the shaft. A piece of stiff brass is soldered to one end of a bicycle spoke and bent around the propeller. A small nut made by cutting a spoke nipple is screwed on the end to hold the propeller in position. (The same illustration shows another very good method of fastening the propeller to the shaft. The end of the shaft is filed to a sharp point, bent into the shape shown in the illustration and then driven into the propeller. A small pin hole should be made in the propeller at the place where the sharp point is to enter in order to avoid the possibility of splitting.)
FIG. 34. Method of forming sockets for joining struts, etc., by cutting from sheet metal.
There are two methods of making propellers by steaming and bending thin wood. American whitewood and spruce are the best woods for the purpose. After steaming place one end of the strip in a vise and holding the other in the fingers twist it into the right shape. Fasten it in position and allow it to remain so until dry. Then give it a coat of varnish to prevent the absorption of moisture and consequent warping. The method of fastening the shaft, which in this case is a piece of piano wire or a bicycle spoke is illustrated in Fig. 35. Two small pieces of wood shaped like a half cylinder and having a groove cut on the curved surface are glued on either side at the centre. The shaft is then bent around and twisted.
FIG. 35. Bent wood propellers and the methods of fastening them to the shaft.
