Manufacturing Processes Multiple Choice Questions on “Bevel Gear Cutting”.
1. Which of the following methods delivers the better rolling performance and higher strength of the manufactured bevel gear?
a) Face milling completing and hard finishing by grinding
b) Face hobbing and hard finishing by lapping
c) Face milling with five-cut and hard finishing by lapping
d) Face milling completing and hard finishing by lapping
Answer: a
Clarification: Bevel gear grinding improves all important properties such as strength, noise characteristics and efficiency. It also requires less investment and follows simple working principle. Lapping typically improves the wear properties of gear tooth, and corrects minute errors in involute profile, helix angle, tooth spacing and concentricity created in the forming, cutting or in the heat treatment of the gears. But the main disadvantage of lapping is that, it is a mating process; two gears that have been matched by lapping should be operated as a set and also replaced as a set, rather than singly.
2. Face milled gear sets are manufactured in_____
a) Single-indexing—one slot at a time
b) Single-indexing¬—two slots at a time
c) Double-indexing—two slots at a time
d) All the slots at a time
Answer: a
Clarification: The milling machine can cut only one tooth/slot at a time. After cutting one tooth, indexing crank is rotated by calculated amount thus taking the workpiece to the proper position for cutting the next tooth.
3. A certain tooth depth taper is applied in all face milled completing bevel gears.
a) True
b) False
Answer: a
Clarification: If a pointed topland occurs on the toe, the teeth of the one member will not fit and roll in slots of the other members if both members are manufactured in a completing process. It is calculated in such a way that it generates a slot taper that splits the difference in circumference between toe and heel in an equal slot and tooth thickness taper.
4. What causes an un-proportionally thin and high tooth in the toe region, and a short and thick tooth at the heel?
a) Difference in PCDs of the generating gears
b) Error in indexing while manufacturing
c) Difference in outer and inner circumference of the generating gear
d) Difference in feed rates
Answer: c
Clarification: The difference in outer and inner circumference of the generating gear causes an extreme tooth thickness taper that leads to uneven tooth profile.
5. Face hobbed gear sets are manufactured as continues indexing.
a) True
b) False
Answer: a
Clarification: Face hobbed gears are manufactured using continuous indexing, while the outside blade and the following inside blade of one blade group cut one slot, the following blade group will enter the next slot.
6. Which of the following is a result of the constant relative indexing motion between cutter and workpiece?
a) Un-equal tooth thickness taper
b) Un-equal slot taper
c) Equal slot taper and un-equal tooth thickness taper
d) Natural sloth taper and equal tooth thickness taper
Answer: d
Clarification: The constant relative indexing motion results in an equal split of the inner and outer circumference on the toe and heel as well as an equal split between toe and heel along the entire face . This leads to a natural slot taper and equal tooth thickness taper.
7. It is possible to grind face hobbed gears.
a) True
b) False
Answer: b
Clarification: Face milled gears have no slot taper but a large thickness taper, on the other hand, face hobbed gears have an equal slot and tooth thickness taper. Therefore, it is impossible to grind face hobbed gears using a cup-shaped grinding wheel.
8. Face hobbed bevel gear sets tend to have their involute point location_____
a) on the flank centre
b) on the addendum circle
c) between addendum and dedendum circle
d) between flank centre and the heel
Answer: d
Clarification: Face hobbed bevel gear sets tend to have their involute point location between the flan centre and the heel, which gives them the reputation of being forgiving with respect to gearbox and gear set deflections.
9. How many indexing methods are there for cutting a gear?
a) 2
b) 4
c) 6
d) 8
Answer: b
Clarification: There are total four indexing methods as listed below—
1) Direct indexing 2) Simple indexing 3) Compound indexing 4) Differential indexing.
10. What will be the indexing to cut 30 teeth on a gear using simple indexing method?
a) Rotate indexing crank by 5 holes in 15 holes circle
b) Rotate indexing crank by 10 holes in 15 holes circle
c) Rotate indexing crank by one complete turn and 7 holes in 21 holes circle
d) Rotate indexing crank by one complete turn and 10 holes in 15 holes circle
Answer: c
Clarification: Crank movement = 40/N
= 40⁄30
=1 10⁄30
=1 1⁄3
Case 1: Multiplying both numerator and denominator by 5
We will get,
Crank movement = 1 5⁄15
Denominator becomes ‘15’, therefore select 15 hole circle plate.
This means that after each operation rotates indexing crank by one complete turn and 5 holes in 15 holes circle.
Case 2: Multiplying both numerator and denominator by 7
We will get,
Crank movement = 1 7⁄21
Denominator becomes ‘21’, therefore select 21 hole circle plate.
This means that after each operation rotates indexing crank by one complete turn and 7 holes in 21 holes circle.
Similarly, we can multiply and divide by other numbers too, provided that the index plate with required holes is available.