# Machine Design Questions and Answers – System of Gear Tooth

This set of Machine Design Multiple Choice Questions & Answers (MCQs) focuses on “System of Gear Tooth”.

1. There are ____ standard systems for the shape of gear teeth.
a) 1
b) 2
c) 3
d) 4

Explanation: 14.5⁰ full depth involute system, 20⁰ full depth involute system and 20⁰ stub involute system.

2. When the number of teeth reaches infinity, circle radius approaches infinity the gear becomes an infinite loop.
a) True
b) False

Explanation: It becomes a rack with straight sided teeth.

3. Which of the following statements are not true?
a) Increasing pressure angle improves the tooth strength
b) Contact duration is decreased with increase in pressure angle
c) 20⁰ pressure angle has quieter operation then 14.5⁰
d) All of the statements are true

Explanation: Lower the pressure angle, quieter is the operation. Lower the pressure angle, lower is the breadth of the tooth at root.

4. 20⁰ stub involute system have comparatively smaller interference.
a) True
b) False

Explanation: They have shorter addendum and shorter dedendum.

5. Which of the following have stronger teeth?
a) Stub teeth
b) Full depth teeth
c) Both have equal strength
d) Can’t be determined

Explanation: Smaller moment arm of bending force leads to stronger stub teeth.
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6. As the module increases, index of size of gear decreases.
a) True
b) False

Explanation: Module is the measure of size of index of the gear tooth.

7. Crowning is an abrasive process that debars the gear strength.
a) True
b) False

Explanation: Crowningis used to strengthen the tooth.

8. Inaccuracies in tooth profile lead to concentration of pressure on the middle of tooth.
a) True
b) False

Explanation: Inaccuracies lead to shift of pressure at the end of tooth which can be improved by crowning.

9. A pair of spur gears consist of 25 teeth pinion meshing with a 115 teeth gear. The module is 5mm. Calculate the centre distance.
a) 280mm
b) 269mm
c) 350mm
d) 305mm

Explanation: C = m(z(p)+z(g))/2.
C = 5(25 + 115)/2 => 700/2 => 350mm.

10. A pair of spur gears consist of 25 teeth pinion meshing with a 115 teeth gear. The module is 5mm. Calculate pitch circle diameter of the pinion.
a) 95mm
b) 105mm
c) 115mm
d) 125mm

Explanation: D = 5×25 = 125mm.

11. A pair of spur gears consist of 25 teeth pinion meshing with a 115 teeth gear. The module is 5mm. Calculate the pitch circle diameter of the gear.
a) Cannot be determined
b) 31mm
c) 475mm
d) 575mm

Explanation: D = 5×115 = 575mm.

12. A pair of spur gears consist of 25 teeth pinion meshing with a 115 teeth gear. The module is 5mm. Calculate the addendum.
a) None of the listed
b) 4.75mm
c) 5.25mm
d) 5mm

Explanation: H=m=5mm.

13. A pair of spur gears consist of 25 teeth pinion meshing with a 115 teeth gear. The module is 5mm. Calculate the dedendum.
a) 4.75mm
b) 5mm
c) 6.25mm
d) 6.68mm

Explanation: H = 1.25xm = 1.25x5mm = 6.25mm.

14. A pair of spur gears consist of 25 teeth pinion meshing with a 115 teeth gear. The module is 5mm. Calculate the tooth thickness.
a) 6.23mm
b) 5.44mm
c) 7.854mm
d) 8.16mm

Explanation: T = 1.5708xm = 1.5708x5mm = 7.854mm.

15. A pair of spur gears consist of 25 teeth pinion meshing with a 115 teeth gear. The module is 5mm. Calculate the bottom clearance.
a) None of the listed
b) 1.75mm
c) 2.5mm
d) 1.25mm

Explanation: C = 0.25m = 0.25x5mm = 1.25mm.

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