Template machining utilizes a simple, single-point cutting tool that is guided by a template. However, the equipment is specialized, and the method is seldom used except for making large-bevel gears. The generating process is used to produce most high-quality gears. This process is based on the principle that any two involute gears, or any gear and a rack, of the same diametral pitch will mesh together. | THREAD CUTTING AND FORMING 1067 Template machining utilizes a simple single-point cutting tool that is guided by a template. However the equipment is specialized and the method is seldom used except for making large-bevel gears. The generating process is used to produce most high-quality gears. This process is based on the principle that any two involute gears or any gear and a rack of the same diametral pitch will mesh together. Applying this principle one of the gears or the rack is made into a cutter by proper sharpening and is used to cut into a mating gear blank and thus generate teeth on the blank. Gear shapers pinion or rack gear-hobbing machines and bevel-gear generating machines are good examples of the gear generating machines. Gear Finishing To operate efficiently and have satisfactory life gears must have accurate tooth profile and smooth and hard faces. Gears are usually produced from relatively soft blanks and are subsequently heat-treated to obtain greater hardness if it is required. Such heat treatment usually results in some slight distortion and surface roughness. Grinding and lapping are used to obtain very accurate teeth on hardened gears. Gear-shaving and burnishing methods are used in gear finishing. Burnishing is limited to unhardened gears. THREAD CUTTING AND FORMING Three basic methods are used for the manufacturing of threads cutting rolling and casting. Die casting and molding of plastics are good examples of casting. The largest number of threads are made by rolling even though it is restricted to standardized and simple parts and ductile materials. Large numbers of threads are cut by the following methods 1. Turning 2. Dies manual or automatic external 3. Milling 4. Grinding external 5. Threading machines external 6. Taps internal Internal Threads In most cases the hole that must be made before an internal thread is tapped is produced by drilling. The hole size determines the depth of the thread the forces .
