CHAPTER II.

=THE TEETH OF GEAR-WHEELS (Continued).=

=Worm and Worm-Wheel=, or wheel and tangent screw 28 to 31 General description of 28 Qualifications of 28 The wear of 28 =Worm-Wheel Teeth=, the sliding motion of 28 When straight have contact on the centres only of the tooth sides 28 That envelop a part of the worm circumference 28 The location of the pitch line of the worm 28 The proper number of teeth in the worm-wheel 29 Locating the pitch line of the worm so as to insure durability 29 Rule for finding the best location for the pitch line of the worm 29 Increasing the face of the worm to obtain a smoother action 29 =Worms=, to work with a square thread 29 =Worm-Wheels=, applications of 30 =Gear-Wheels= with involute teeth 31 to 34 =Gear Teeth.= Generating the involute curve 31 Templates for marking the involute curve 32 =Involute Teeth=, the advantages of 34 =Gear Teeth=, Pratt and Whitney's machine for cutting templates for 35