6.9 Transmissions

Question 1

What is one of the most popular precision gears?

Answer 1

Spur

Question 2

What teeth do spur gears have?

Answer 2

Straight cut, internal or external.

Question 3

What are the larger and smaller wheels of spur gears called?

Answer 3

Larger is spur and smaller is pinion.

Question 4

Where are external spur gears used?

Answer 4

Change of speed is required and the shafts are parallel.

Question 5

Where are internal spur gears used?

Answer 5

When a speed change is required whilst maintaining an overall minimum diameter.

Question 6

What is the benefit of spur gears with helical cut teeth?

Answer 6

Carry heavier loads at higher speeds, quieter and smoother.

Question 7

Why can helical spur gears carry more load?

Answer 7

They have more teeth = more surface area with which to carry load.

Question 8

What is the maximum angle of helical cut teeth?

Answer 8

20 degrees

Question 9

What is a herringbone gear?

Answer 9

Double helical gear used for larger forces.

Question 10

What are bevel gears?

Answer 10

Gears that meet at 90 degrees.

Question 11

What is the theoretical point of intersection called on bevel gears?

Answer 11

Apex

Question 12

What type of bevel gear is better in most aspects?

Answer 12

Spiral bevel.

Question 13

What is a hypoid gear?

Answer 13

A variation of the bevel gear, however they suffer from heavy sliding contact and need extreme pressure lubricant.

Question 14

How does a worm gear work?

Answer 14

Consists of the worm screw that drives a worm gear.

Question 15

At what reduction would a worm wheel be unable to drive the worm screw?

Answer 15

20:1

Question 16

How is the speed ratio of worm gears calculated?

Answer 16

Dividing the number of thread starts on the worm screw into the number of teeth on the worm wheel.

Question 17

When is no mechanical advantage gained?

Answer 17

If the drive and driven have the same number of teeth.

Question 18

What is the purpose of an idler gear?

Answer 18

Used between two gears to either make the input direction the same as the output of fill a gap between two gears.

Question 19

Does the idler gear change the speed ratio?

Answer 19

No

Question 20

How can the direction of rotation be worked out in a gear train?

Answer 20

By counting them from the input-
even- same rotation
odd- opposite

Question 21

What is the aim of a reduction gearbox?

Answer 21

Lower the speed but maintain torque.

Question 22

What is backlash?

Answer 22

Describes the clearance between the teeth allowing for a film of lubrication.

Question 23

What would excessive backlash be a sign of?

Answer 23

Worn gearing.

Question 24

What types of belt are there?

Answer 24

Friction drive or positive drive.

Question 25

What is the benefit of positive drive belts?

Answer 25

Teeth driven belts with no slip.

Question 26

What are v belt pulleys used for?

Answer 26

Transmitting power between two parallel axles.

Question 27

What are roller chains composed of?

Answer 27

Link plates, pins and rollers and bushes.

Question 28

Where can leaf chains be used?

Answer 28

Low speed