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Unit 3.4
Question | Answer |
---|---|
Gear train | combining a series of gears |
External gears | have the teeth cut into the outside rim of a metal or plastic disk. |
Internal gears | have the teeth located on the inner surface of a hollow cylinder or ring. |
Helical gears | Gears that are cylindrical in shape but the teeth are curved or helical. |
Worm gears | a special helical gear that has only one tooth that spirals about a central axis like a screw. |
Bevel gears | angled like a cone with teeth cut into the conical faces. |
Rack and pinion | gear train consists of a single spur or helical gear that meshes with teeth in a straight rod with teeth cut into it. |
Planetary gear train | uses a combination of spur gears and a ring gear in a concentric arrangement that maintains a central axis of rotation. |
Diametral pitch | represents the number of teeth on a gear measured in teeth per inch. |
Pitch circle | an imaginary circle that passes through the midpoint of each tooth. |
Pressure angle | the angle of the face of the tooth that sits above the pitch circle. |
Addendum | the portion of the tooth that is above the pitch circle. |
Addendum circle | an imaginary circle that traces through the tops of the teeth, equaling the maximum diameter of the gear. |
Dededum | the portion of the tooth that is below the pitch circle. |
Dededum circle | an imaginary circle that traces through the bottom of each tooth and tooth space. |
Tooth clearance | the space between the top of a tooth and the bottom of the tooth space on two meshing gears. |
Bore | a pre-sized hole drilled through the center of the gear to accommodate a shaft or axle. |
Keyway | a small square channel cut into the gear across the borehole or cut into the axle shaft. |
Key | a small metal prism that locks the gear and the shaft together by fitting into the keyway, essentially overlapping the joint. |
Fulcrum | 1. The pivot point of a lever. 2. The axis of rotation of a moment arm. |
Lever arm | the distance of the lever from the fulcrum to where a force is applied or a weight sits. |
Gear ratio | the ratio of the pitch diameters of each pair of meshing gears |
Driver gear | the gear turned by the motor |
Output gear | the gear that is turned or driven by the driver gear |
Backlash | excessive distance between the tooth on one gear and the tooth space or gap on the mating gear. |
Gear gnashing | occurs when gear teeth jump over tooth spaces and the tops of gears grind past one another. |
Sprocket | A wheel with metal teeth that mesh with a chain. |
Compound gear train | at least two of the gears have the same axis of rotation. |