A pinion gear with 14 teeth drives a spur gear with 42 teeth at 140 RPM. Determine the speed of the pinion gear?

A pinion gear with 14 teeth drives a spur gear with 42 teeth at 140 RPM. Determine the speed of the pinion gear?

• A. 420 RPM
• B. 140 RPM
• C. 70 RPM
• D. 210 RPM

Answer: (A)

In gear trains, the speed ratio is the inverse of the gear teeth ratio: the gear with more teeth rotates more slowly. With a pinion of 14 teeth meshing with a 42-tooth spur gear, the teeth ratio is 14:42, which simplifies to 1:3. This means the pinion must rotate three times for every one rotation of the spur gear. Since the spur gear is given to rotate at 140 RPM, the pinion speed is three times that: 3 × 140 = 420 RPM. So the pinion spins at 420 RPM.

In gear trains, the speed ratio is the inverse of the gear teeth ratio: the gear with more teeth rotates more slowly. With a pinion of 14 teeth meshing with a 42-tooth spur gear, the teeth ratio is 14:42, which simplifies to 1:3. This means the pinion must rotate three times for every one rotation of the spur gear.

Since the spur gear is given to rotate at 140 RPM, the pinion speed is three times that: 3 × 140 = 420 RPM. So the pinion spins at 420 RPM.