To find the center of the block two lines should be drawn from the opposite corners, their point of meeting being approximately in the center—near enough for all practical purposes to insure greater accuracy. Similar lines should be drawn from the corners on theBottomside of the block of wood. A hole ³â„₃₂ of an inch in diameter should be bored through the center thus obtained, through which the propeller shaft will be inserted when the propeller is finished. The two sections of the propeller blades drawn in diagrammatical form on theTopof the block, should be marked respectivelyBlade 1andBlade 2, as shown indiagram 1. The block is then ready for the commencement of the actual cutting. In cutting out the propeller,Blade 1should be held in the left hand and the knife in the other, with the blade of the knife on the straight edge ofBlade 1. The cutting should be carried out very carefully with attention constantly paid toFig. 2, and should be stopped when the line shown inFig. 2has been reached. The semi-blade should then be sandpapered until a small curve is obtained by which the propeller will be enabled to grip the air.