7.6 Fits And Clearances Flashcards
What’s the high limit
The largest acceptable size for a particular dimension
What are the two types of clearance fit
Running and free running
What two subsections can transition fits be divided into
Push and light press
What’s an interference fit
Where the hole is smaller than the item being fitted
What subsections are interference fits split up into
Drive , press, force
What’s a shrink fit
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
What is known as a good fit?
Josh Willy + Sean/Lewis bums
How does wear occur?
When there is motion between 2 parts (Willy and bum)
What are the limits for twists?
If released and it untwisted it is below elastic limit, if stays same shape is above elastic limit
What are the 4 dimensions for wear?
Dimensions new, clearance new, permissible worn dimensions, permissible worn clearance
What is a dial test indicator? (DTI)
Precision tool used to measure movement
How should clearance fit components be assembled?
Light hand pressure
How should interference fit components be assemble?
With force
What is the ISO system?
It between shafts and bearing
What’s a small limit
The smallest acceptable size for a certain dimension
What’s the difference between the high and the low limit
The tolerance
What is the allowance
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
If a parts are intended to move together then what documentation must it have
Schedule of fits and clearances for the aircraft
What characteristics does the schedule or fits and clearances intail
Ovality
Bow of shaft
Twist of shaft
What does it mean if an item is bowed
The centre line of the item is not straight
How do you measure the amount of twist an object is under while in operation
By using a Strain gauge
If the shaft remains twist after the load has been removed, it has been????
Loaded above it’s elastic limit
What are the four dimensions for the limits of wear
Dimensions new
Permissible worm dimension
Clearance new
Permissible worn clearance
What does dimensions new mean
Relates to size of part when it’s new and shows relevant dimensions
What does permissible worn dimensions mean
The size which a part may wear too before it’s unserviceable
What does clearance new mean
Desired clearance in limit form
(Interference fits are quoted as negative clearances)
What does permissible worn clearance mean
The maximum allowable clearance when reassembling a component
What are the two methods for checking shafts, bearings and other parts
Dial test indicator (DTI)
Checking method
What is a DTI and what does it do
Dial test indicator
Precession measuring instrument that can be used to measure the amount of movement between certain engine and airframe parts
What is a checking method (Dont think we will need to know)
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
