Gear Drives

Question 1

What is the difference between a speed reducer and a speed increaser gear drive in terms of the relationship between the size of the drive gear and the driven gear?

Answer 1

Pinion: smaller gear, does more work
if pinion gear drives it is is a speed reducer unit
if gear drives it it is a speed increaser unit

Question 2

What degree of pressure angle do most new gears have?

Answer 2

20 DEGREES

Question 3

What is the difference between gear tooth clearance and backlash

Answer 3

Tooth clearance: distance between the top of the tooth of one gear and the bottom of meshing tooth space
Backlash: amount of SIDE clearance of a gear tooth when two teeth mesh

Question 4

Pinion gear

Answer 4

smaller gear

Question 5

Idler gear

Answer 5

an intermediate gear used to make the driver and driven gears rotate in the same direction

Question 6

gear ratio

Answer 6

ratio between number of teeth on driven gear to the teeth on the driver gear

Question 7

Pressure angle

Answer 7

determines shape of tooth. All meshing gears should have some Pressure angle. The slant at the top

Question 8

Diametral potch

Answer 8

SIZE of gear teeth that specifies the number of teeth per inch of the gear’s pitch diameter.

Question 9

Clearance

Answer 9

distance between top of tooth of gear and bottom of the meshing gear

Question 10

Backlash

Answer 10

side clearance between two meshing gears

Question 11

What are the two formulas for calculating the number of teeth in a gear

Answer 11

N= OD x DP - 2

N=PD x DP

Question 12

What are the three major configurations of spur gear drives

Answer 12

External
Internal
rack and pinion

Question 13

What are the disadvantages of spur gears when compared with other gear types

Answer 13

• Noisier
• more vibration
• limited to low or moderate speeds
• only two teeth can mesh at once so its not as smooth sets

Question 14

what are the four types of bevel gears commonly used in industry

Answer 14

straight
spiral
zero bevel
hypoid

Question 15

What are the are the advantages of helical gears

Answer 15

• greater tooth length=greater load and power capabilties
• more teeth meshing
• smoother and quieter
• load is spread over entire surface of tooth

Question 16

Why would a double helical gear used rather than a single helical gear?

Answer 16

the problem is shaft end, or axial thrust,

double helical gears create equal but opposing forces to cancel out the thrust

Question 17

Herringbone gears are more difficult and expensive to machine than standard helical gears, but where are these types of gears preferred

Answer 17

They are preferred where you need stronger and used with very heavy loads and high speeds

Question 18

When are bevel gears mainly used

Answer 18

Intersecting shafts

Question 19

When are worm gears generally used, and what advantages do they have

Answer 19

• high ratios in compact areas
• quieter, less vibration because of sliding contact
• handle shock loads well

Question 20

What is meant by the statement “Worm gears tend to be self locking”?

Answer 20

self locking is when motion cannot be started by applying torque to the output shaft (worm gear)

Question 21

What is the another name for a bevel gear that have the same number of teeth and 90 degree shafts

Answer 21

miter gears

Question 22

To ensure that a gear drive cannot be reversed what should you use

Answer 22

backstop

Question 23

Which type of gearbox approaches 99 efficiency?

Answer 23

helical gearbox

Question 24

service factor

Answer 24

constant used to multiply the horsepower by a multiplier in the selection of gearbox

Question 25

most common gear profil

Answer 25

The involute gear profile where the profiles of the teeth are involutes of a circle

The contact between teeth occur at a single instantaneous point

Question 26

gears of difference pressure angles are

Answer 26

NOT interchangeable

Question 27

pitch diameter

Answer 27

is the diameter of that instantaneous point to the opposite side

Question 28

straight bevel gears

Answer 28

have same advantage/disadvantage as spur gears so speed and gear ratio should be kept low

They are angled

Question 29

spiral bevel gears

Answer 29

are bevel gears that provide the advatnage that helical gears do for spur gears.

smoother
less noise
higher speeds
higher loads