36 mm and 9071 mm respectively the exact distance

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Unformatted text preview: t distance between the two shafts must be 604.73 mm. Ans. x′ = 13.6. Reverted Gear Train When the axes of the first gear (i.e. first driver) and the last gear (i.e. last driven or follower) are co-axial, then the gear train is known as reverted gear train as shown in Fig. 13.4. We see that gear 1 (i.e. first driver) drives the gear 2 (i.e. first driven or follower) in the opposite direction. Since the gears 2 and 3 are mounted on the same shaft, therefore they form a compound gear and the gear 3 will rotate in the same direction as that of gear 2. The gear 3 (which is now the second driver) drives the gear 4 (i.e. the last driven or follower) in the same direction as that of gear 1. Thus we see that in a reverted gear train, the motion of the first gear and the last gear is like. Let T1 = Number of teeth on gear 1, Fig. 13.4. Reverted gear train. r1 = Pitch circle radius of gear 1, and N 1 = Speed of gear 1 in r.p.m. Similarly, T2, T 3, T 4 = Number of teeth on respective gears, r2, r3, r4 = Pitch circle radii of respective gears, and N2, N 3, N 4 = Speed of respective gears in r.p.m. Chapter 13 : Gear Trains l 435 Since the distance between the centres of the shafts of gears 1 and 2 as well as gears 3 and 4 is same, therefore r1 + r2 = r3 + r4 ...(i) Also, the circular pitch or module of all the gears is assumed to be same, therefore number of teeth on each gear is directly proportional to its circumference or radius. ∴ *T 1 + T 2 = T 3 + T 4 and Speed ratio = ...(ii) Product of number of teeth on drivens Product of number of teeth on drivers N1 T2 × T4 = N 4 T1 × T3 or ... (iii) From equations (i), (ii) and (iii), we can determine the number of teeth on each gear for the given centre distance, speed ratio and module only when the number of teeth on one gear is chosen arbitrarily. The reverted gear trains are used in automotive transmissions, lathe back gears, industrial speed reducers, and in clocks (where the minute and hour hand shafts are co-axial). Example 13.3. The speed ratio of the reverted ge...
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