7.6 Fits And Clearances

Question 1

What’s the high limit

Answer 1

The largest acceptable size for a particular dimension

Question 2

What are the two types of clearance fit

Answer 2

Running and free running

Question 3

What two subsections can transition fits be divided into

Answer 3

Push and light press

Question 4

What’s an interference fit

Answer 4

Where the hole is smaller than the item being fitted

Question 5

What subsections are interference fits split up into

Answer 5

Drive , press, force

Question 6

What’s a shrink fit

Answer 6

Extreme type of interference fit and is where the shaft is much larger than the whole so is achieved by heating the outer part so it expands

Question 7

What is known as a good fit?

Answer 7

Josh Willy + Sean/Lewis bums

Question 8

How does wear occur?

Answer 8

When there is motion between 2 parts (Willy and bum)

Question 9

What are the limits for twists?

Answer 9

If released and it untwisted it is below elastic limit, if stays same shape is above elastic limit

Question 10

What are the 4 dimensions for wear?

Answer 10

Dimensions new, clearance new, permissible worn dimensions, permissible worn clearance

Question 11

What is a dial test indicator? (DTI)

Answer 11

Precision tool used to measure movement

Question 12

How should clearance fit components be assembled?

Answer 12

Light hand pressure

Question 13

How should interference fit components be assemble?

Answer 13

With force

Question 14

What is the ISO system?

Answer 14

It between shafts and bearing

Question 15

What’s a small limit

Answer 15

The smallest acceptable size for a certain dimension

Question 16

What’s the difference between the high and the low limit

Answer 16

The tolerance

Question 17

What is the allowance

Answer 17

When two components are to be fitted together, the difference between the high limit of the inside component and the low limit of the surrounding component

Question 18

If a parts are intended to move together then what documentation must it have

Answer 18

Schedule of fits and clearances for the aircraft

Question 19

What characteristics does the schedule or fits and clearances intail

Answer 19

Ovality
Bow of shaft
Twist of shaft

Question 20

What does it mean if an item is bowed

Answer 20

The centre line of the item is not straight

Question 21

How do you measure the amount of twist an object is under while in operation

Answer 21

By using a Strain gauge

Question 22

If the shaft remains twist after the load has been removed, it has been????

Answer 22

Loaded above it’s elastic limit

Question 23

What are the four dimensions for the limits of wear

Answer 23

Dimensions new
Permissible worm dimension
Clearance new
Permissible worn clearance

Question 24

What does dimensions new mean

Answer 24

Relates to size of part when it’s new and shows relevant dimensions

Question 25

What does permissible worn dimensions mean

Answer 25

The size which a part may wear too before it’s unserviceable

Question 26

What does clearance new mean

Answer 26

Desired clearance in limit form
(Interference fits are quoted as negative clearances)

Question 27

What does permissible worn clearance mean

Answer 27

The maximum allowable clearance when reassembling a component

Question 28

What are the two methods for checking shafts, bearings and other parts

Answer 28

Dial test indicator (DTI)
Checking method

Question 29

What is a DTI and what does it do

Answer 29

Dial test indicator
Precession measuring instrument that can be used to measure the amount of movement between certain engine and airframe parts

Question 30

What is a checking method (Dont think we will need to know)

Answer 30

Engine crankshaft runout is checked with a DTI by assembling the instrument onto a stand and positioning it onto a smooth part of the crankshaft, then adding a load to the DTI, pressing it u0 against the shaft so the pointer deflects a few thousands of an inch.
DTI is the zeroed, as crankshaft is turned, the DTI will indicate the amount of deviation in both directions