rotation, the direction of rotation, and the amount of torque. Planetary Geartrains Planetary geartrains: the centers of certain gears move. And their motion is similar in some respects to the orbit of a planet around a star. The planet gear rotates about its own center, meshes with the sun gear, and orbits as a whole about the center of the sun gear. The link that connects the centers of the two gears is called the carrier. It can rotate as well about one of its ends When multiple planet gears are present to reduce noise, vibration and force, the carrier is sometimes called the spider. Bevel gea The teeth shape of bevel gear are like ordinary spur gears, but the tooth surfaces are made up of conical elements Helical gear The teeth of helical gears are still formed on a cylinder. However the teeth are not parallel to the gear's shaft Instead, the teeth on a helical gear are inclined at an angle so that each tooth wraps on the gear's cylinder in the shape of a shallow helix. Property of Helical Gear As helical gears rotate, each tooth comes first into engagement on one side, with contact spreading across the tooth as rotation continues Transmit motion between parallel shafts. Helix angle is the same on each gear, but one gear must have a right-hand helix and the other a left-hand helix Applications of Helical Gear LEss noise LEss vibration HIgher rotating speeds I Greater torque and power COmplex to analyze and manufacture I Subjected to a thrust load, This can be eliminated by using double he ical or herring bone gears. Worm and Worm Gear Worm gears are similar to crossed helical gears. The pinion or worm has a small number of teeth, usually one to four, and since they completely wrap around the pitch cy linder they are called threads. Its mating gear is called a worm gear. For each revolution of the worm, the worm gear advances by just on tooth in its rotation SIGNIFICANT FIGURE Significant figures"are all the dig its in a measurement that are known with certainty plus a last digit that must be estimated The last significant digit in a measured quantity is the first digit of uncertaintyrotation, the direction of rotation, and the amount of torque. Planetary Geartrains Planetary geartrains: the centers of certain gears move. And their motion is similar in some respects to the orbit of a planet around a star. The planet gear rotates about its own center, meshes with the sun gear, and orbits as a whole about the center of the sun gear. The link that connects the centers of the two gears is called the carrier. It can rotate as well about one of its ends. When multiple planet gears are present to reduce noise, vibration and force, the carrier is sometimes called the spider. Bevel Gear The teeth shape of bevel gear are like ordinary spur gears, but the tooth surfaces are made up of conical elements. Helical Gear The teeth of helical gears are still formed on a cylinder. However the teeth are not parallel to the gear’s shaft. Instead, the teeth on a helical gear are inclined at an angle so that each tooth wraps on the gear’s cylinder in the shape of a shallow helix. Property of Helical Gear As helical gears rotate, each tooth comes first into engagement on one side, with contact spreading across the tooth as rotation continues. Transmit motion between parallel shafts. Helix angle is the same on each gear, but one gear must have a right-hand helix and the other a left-hand helix. Applications of Helical Gear lLess noise lLess vibration lHigher rotating speeds lGreater torque and power lComplex to analyze and manufacture lSubjected to a thrust load, This can be eliminated by using double helical or herringbone gears. Worm and Worm Gear Worm gears are similar to crossed helical gears. The pinion or worm has a small number of teeth, usually one to four, and since they completely wrap around the pitch cylinder they are called threads. Its mating gear is called a worm gear. For each revolution of the worm, the worm gear advances by just on tooth in its rotation. SIGNIFICANT FIGURE “Significant figures” are all the digits in a measurement that are known with certainty plus a last digit that must be estimated. The last significant digit in a measured quantity is the first digit of uncertainty