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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. |