The RPM of "D" is 600 and hobbed with 46 teeth. If gears "A", "B", and "C" have 94, 80, and 30 teeth respectively, the RPM of "A" in the gear train illustration is __________. See illustration MO-0088.
• Use the basic gear relationship for each mesh: (RPM₁ × Teeth₁) = (RPM₂ × Teeth₂) for external gears • In a compound gear train, gears on the same shaft turn at the same RPM; only the tooth counts of the meshing pairs affect the speed ratios • The overall speed ratio between the first and last gears is the product of the individual stage ratios
• From the illustration, identify clearly which gears are physically meshed and which gears are on the same shaft. How many distinct shafts are there? • Starting from gear D (600 RPM, 46 teeth), write the RPM relationship for the first mesh, then carry that RPM across any shared shaft, and then write the relationship for the second mesh to reach gear A. • After you set up your equations, check whether the RPM of A should be higher or lower than 600 RPM based on the relative tooth sizes of the driving and driven gears in each mesh.
• Make sure you are pairing the correct teeth numbers with the correct gears: A = 94 teeth, B = 80 teeth, C = 30 teeth, D = 46 teeth. • Confirm which gears share a shaft in the illustration (those gears have identical RPM). This is critical before multiplying ratios. • After computing, verify that your final RPM value for A matches the direction of change expected from the tooth ratios (does each mesh step the speed up or down?).
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