Fits And Clearances Flashcards
What is a Fit?
How tight or loose two joined parts fit together
What is a shaft?
A rounded part that fits into a bore including pegs, axles, bolts, pins, etc
What is Nominal Size?
Measurement calculated in the draft also a dimension
Idea, dimension
What is a tolerance?
A deviation from the Nominal size
What is a Clearance fit?
There will always be some play between the two assembled items when joined
What is a Transition fit?
There can be some play between two assembled items or interference depending on their Nominal sizes
What is an Interference fit?
The hole is always smaller than the shaft and will require force to fit together
What is the difference between a Hole Based system and a Shaft Based system?
Capital letters indicate Hole deviations
Lowercase letters indicate Shaft deviations
Hole Based - the minimum hole size is the basic size
Shaft Based - the maximum shaft size is the basic size
What is a Dial Tester?
Precision instrument for measuring movement between parts
What process is used to harden solid rivets soon after solution heat treatment?
Age hardening
What angle countersinks are available and which is most common?
82 degrees
100 degrees
120 degrees
Most common is 100 degrees
Which rivets require heat treatment?
How many times can they be treated?
D
DD
E
Once
What does AN470DD-5-6 indicate?
Universal head
2024 alloy
5/32 diameter
6/16 length
What is the centre to centre distance of two fasteners in a single row called?
Pitch
What is Sphere of Influence?
The area of sheet metal over which a rivet will achieve a water-tight joint
How is inter-buckling prevented?
The maximum permissible rivet spacing of a pressurised fuselage should be 6D or 18t (whichever is smaller)
Why would you need to dimple material?
Skin is too thin to cut - countersink is shaped (dented) to accept the head of a countersunk fastener by dimpling
Which dimpling process is best used for limited access?
Radius dimpling greater than 100 degrees so cannot nest, dies smaller than radius for getting into hard to reach areas
What refinement to the dimpling process prevents cracking of hard material?
Hot dimpling for 7075
Same as coin
Which dimpling process provides sharply defined edges?
Coin dimpling
What tool is required for reaction riveting?
Rivet gun
What is the meaning of the term percussion riveting?
Hand riveting
What method is preferred for installation of solid fasteners?
Squeeze followed by pneumatic
What tool is required for squeeze riveting?
Squeeze tool
What tool is required for percussion riveting?
Hammer
Dolly
What must be taken into account before countersinking material?
Added thickness due to tape or protective coating
How is depth adjusted on a microstop countersinker?
Pulling sleeve back and turning the stop to increase or decrease the cut. Sleeve is then dropped back into its original position
Where can general requirements of riveting a particular aircraft be found?
SRM
How is a solid rivet removed without damaging the structure?
Centre punch head for drill Drill into head Position punch Snap off head Push out
What system is used to protect hose assemblies from chafing and temperature extremes?
Sleeve:
Heat shrink
Nylon spiral wrap
Teflon
What is the usual corrective/repair action for springs found to be unserviceable?
Replaced
What law of physics pertains to the behaviour of springs and what does it state?
Hooke’s Law
Within its elastic limit it is said to obey Hooke’s Law
