Module 7.6

Question 1

What are the 3 classes of fit?

Answer 1

-Clearance
-Interference
-Transition

Question 2

How are parts with clearance fits assembled?

Answer 2

By light hand pressure or without any force (running or free running) there is play between components

Question 3

Why is no movement possibly after assembly of parts with an interference fit?

Answer 3

Inner part is larger than what it fits into

Question 4

What are the 3 classes of interference fit?

Answer 4

-driving
-force
-shrink

Question 5

When and how are shrink fits used?

Answer 5

When parts are joined to be held in place permanently
Outer member heated to expand or inner member cooled to shrink then allowed to contract/expand to fit tight

Question 6

What is a transition fit?

Answer 6

A fit in between clearance and interference. Mating points are almost the same size

Question 7

What is an allowance?

Answer 7

Difference in dimensions that is necessary to give particular fit

Question 8

What is the correct allowance calculated from?

Answer 8

Difference in high limit of shaft and low limit of hole

Question 9

What is a tolerance?

Answer 9

Total amount of variation in size of a port

Question 10

What are the two types of tolerances?

Answer 10

Uni-lateral
Bi-lateral

Question 11

How are holes and shafts classified in the BSI?

Answer 11

Hole uses 21capital letters
Shaft uses 21 lowercase letters

Question 12

How is the accuracy of each letter classified?

Answer 12

Numbered 1-16

Question 13

How does ISO 286?differ from BS? (ANSI same as ISO)

Answer 13

28 hole classes and shafts
20 accuracy degrees

Question 14

Is the new all system still used?

Answer 14

No

Question 15

What is the BS4500 system based on?

Answer 15

On standard sized holes

Question 16

In an engine shaft the inner part must be smaller than the outer, why is this?

Answer 16

The clearance allows for lubrication

Question 17

During engine/component assembly what are the 3 processes for a correct fit?

Answer 17

-heat/shrink fits, interference fit
-press fits, transition fit
-clearance fit

Question 18

Where is a press fit used in the aircraft engine?

Answer 18

Turbine shaft bearing pressed into a turbine shaft

Question 19

What is an example of a clearance fit on an engine?

Answer 19

Turbine blades into the turbine wheels

Question 20

What is essential to check for on a shaft or tube?

Answer 20

Ends are square with eachother

Question 21

What word describes if the centreline of a shaft is not straight?

Answer 21

Bowed

Question 22

What is increased if a shaft or tube is bowed?

Answer 22

Risk of vibration

Question 23

When does a shaft remain twisted?

Answer 23

When force is applied above the elastic limit

Question 24

With a square sectioned shaft how can trust be checked?

Answer 24

Dial test indicator mounted on a surface gauge

Question 25

What are the 4 wear dimensions?

Answer 25

-dimension new
-permissible worn dimension
-clearance new
-permissible worn clearance

Question 26

How do you check for bowing?

Answer 26

Place a straight edge to the whole length and then insert feeler gauge at max clearance point (1mm over 600mm)

Question 27

What are the methods of checking for twists?

Answer 27

-strain gauges in the shaft
-witness marks between drive and driven

Question 28

What are the 3 methods for checking hole ovality?

Answer 28

-go/no go gauges
-internal micrometers
-callipers

Question 29

What are the two methods for checking shaft ovality?

Answer 29

-micrometer
-ovality gauge

Question 30

What are the DTIs commonly used for?

Answer 30

Checking bowing + ovality