6.9

Question 1

what is the direction of the teeth on a straight cut spur gear

Answer 1

parallel to the shaft’s axis

Question 2

when are external spur gears used

Answer 2

when a change of speed is required and the shafts are parallel

Question 3

when are internal spur gears used

Answer 3

when a change of speed is required whilst not increasing the size

Question 4

what are the benefits of a helical spur gear

Answer 4

carry heavier loads at higher speeds compared to same sized spur gears and run quieter and smoother

Question 5

what are the two types of helical gears

Answer 5

single and double

Question 6

what is a problem caused by a single helical gear that is removed by a double helical gear

Answer 6

a single helical gear produces an axial load on the bearing, but the teeth in the opposite direction cancel that out

Question 7

when are bevel gears used

Answer 7

when 2 different shafts intersect

Question 8

what is the key aspect of a hypoid gear

Answer 8

the shafts are not intersecting

Question 9

what is the main problem for hypoid gears

Answer 9

they suffer from heavy sliding so need very heavy lubricant

Question 10

what is a key advantage of worm gears

Answer 10

they cannot be back driven

Question 11

what is a rack and pinion gear system used for

Answer 11

transmitting rotating movement into linear movement or vice versa

Question 12

what is the mechanical and speed ratio if both gears have the same teeth number

Answer 12

both are 1

Question 13

what is the speed ratio if the drive gear is 8 teeth and the driven gear is 16 teeth

Answer 13

1:2 which means 1/2 the speed

Question 14

what is the mechanical advantage if the drive gear is 8 teeth and the driven gear is 16 teeth

Answer 14

2:1 which means 2 times

Question 15

what is the relationship between gear speed and mechanical advantage

Answer 15

as the speed increases the mechanical advantage decreases and vice versa

Question 16

what direction is an even number in a gear chain

Answer 16

the opposite to the drive gear

Question 17

what direction is an odd number in a gear chain

Answer 17

the same as the drive gear

Question 18

when calculating speed ratio and mechanical advantage in a gear chain what gears are used

Answer 18

the first and last gear

Question 19

what is the primary type of gear used for reduction in aircraft engines

Answer 19

epicyclic (planetary) gears

Question 20

what happens if the gear teeth are too high when joined together

Answer 20

the load is on the small part of the teeth so it will break quicker and easier

Question 21

what happens if the gear teeth are too low when joined together

Answer 21

the teeth will not be lubricated

Question 22

what part of the gear teeth is best for contact with each other

Answer 22

the middle section

Question 23

what is gear backlash

Answer 23

the clearance between the gear teeth and the meshing point

Question 24

what is a belt

Answer 24

a loop of flexible material used to mechanically link or dive 2 or more rotating shafts

Question 25

what happens if the belt is crossed over

Answer 25

the direction of the driven shaft will be reversed

Question 26

what are the two main belt types

Answer 26

friction drive belts and positive drive belts

Question 27

what do friction drive belts need

Answer 27

require tension to have the correct amount of friction

Question 28

what do positive belts rely on

Answer 28

engagement of teeth on the belt with grooves on the pulley

Question 29

why are flat belts not advisable for high speeds

Answer 29

they are more likely to slip off

Question 30

what makes a v belt better than a flat belt

Answer 30

it is wedged into the pulley groove making less likely to slip out

Question 31

how do positive (synchronous) belts work

Answer 31

the belt and pulley work in the same way as a chain as they have teeth that are engaged by the pulley

Question 32

what are v belt pulleys used for

Answer 32

transmitting power between parallel axis

Question 33

what is the difference between a synchronous belt pulley and belt

Answer 33

the teeth are on the pulley rather than the belt

Question 34

what does a stepped or cone pulley drive allow the user

Answer 34

to change the speed ratio and mechanical advantage of the gears without changing the belt

Question 35

what equipment uses a stepped or cone pulley drive

Answer 35

a pillar drill

Question 36

how does a chain and sprocket drive work

Answer 36

a roller chain engages with 2 or more toothed wheels called sprockets

Question 37

what is a leaf chain and what is it used for

Answer 37

a chain made of only link plates and pins used for tensile strength by pulling at either end

Question 38

what is an advantage of chain drives

Answer 38

the chain cannot slip off

Question 39

what is a disadvantage of chain drives

Answer 39

heavy, noisy and more expensive