Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

395 OF ENGINEEBING FORMØLÆ. Teeth of Wheels, If noi made epicycloidal, are frequently struck out with com- passes, the pitch point A being the centre from wh’ch .ha point of the next tooth B C is struck with radius A B, the por- tion B D being radial. The following plan is adopted in America for determining the curves of teeth: P = Pitch, N = No. of teeth. Set off from the pitch line at A, a line B A 0 at an angle of 75° with a line radiating from the centre of the wheel to the edge of the tooth •, lay off from A, A B = 2 (N — 11) ’1 p V From centre B strike out E F, and from centre C strike out ü H. A ruck is treated as a wheel of 200 teeth.