6.5 Fastners Flashcards
What is a thread formed on a cylinder known as
A straight or parallel thread
When a thread is cut in a clockwise direction what is it known as
A right hand thread
When a thread is cut anti clockwise what is it known as
Left hand thread
What were the main threads in Britain and America.
- British Standard (BS) and British Association (BA)
- American National (AN)
What did the American and British threads get replaced with
Unified threads
What are the 3 main British thread forms
- (BSW) British standard course thread
- (BSF) The finer version of the whiteorth
- (BSP) Another fine example of the whiteorth
What are BA threads used for
Fine pitch used for sizes below 1/4 inch diameter only
47.5°
What is the definition of a bolt
It is tightened with a nut
How much of a threat should be protruding though a bolt when tightened
At least 1/32 of an inch or one full chamfer
What should the grip length of a bolt be equal to
The thickness of the material
What is the maximum amount of washers allowed to adjust grip length
3
What are the 4 types of stud available
Standard
Waisted
Shouldered
Stepped
What is the most widely used stud
Standard or plain
When are waisted studs used
Used where strength has to be retained but weight saving is required
When are stepped studs required
To provide a stronger anchorage than plain studs when they are being inserted in to soft material
When are shouldered studs used
Where maximum rigidity is required against lateral stresses
What are the 3 methods of inserting studs
- Stud box
- Stud insertion tool
- Lock nuts
Why are the two main methods of stud removal
- Filed flats
- Ezi outs
When are self tapping screws used
To secure thin gauge sheet metal parts when nuts and bolts are impractical or too expensive
What are the 4 main categories of nuts
- Non self locking nuts
- Locking nuts
- High temp self locking nuts
- Low temp self locking nuts
When must shear castle nuts be used
Used only for shear loads on clevis bolts
What would a castle nut be used for
Designed to fit on standard airframe bolts and designed to take shear or tensile loads
Where must a slotted engine nut only be used
Only on engines, they are not approved to be used on airframe
Where would wing nuts be used
Mainly used on hose clamps and battery connections. Normally tightened by fingers
What is important to remember about nylock stiffnuts
Low temp only
What characteristics make up an oddie stiffnut
6 springy tongues that spring inwards
What are the difference between aerotight and philidas
Aerotight - slot through the bolt
Philidas - a groove around the bolt
When would anchor nuts be used
When a slight range of movement is needed
What temperatures would high temp self locking nuts be used
When temperatures exceed 120°c
All metal and usually made from cres, steel alloy, cres silver plated
When would low temp self locking nuts be used
Where temperatures will not exceed 121°c
When should you not reuse nylon lock nuts
If they can be done up finger tight
What sort of tolerance across its flats does a helicoil inset have
0.0005mm
What is the purpose of a helicoil.
To protect the threads of a soft threaded material a helicoil insert can be inserted. And for stripped threads
What are the two types of helicoil insert available
- The standard type provides a free running thread
- The screw lock type provides a resilient internal locking thread
In ordinary thread assemblies how much of the load does the first thread take
45-50% of the total load
On a helicoil insert how much load distribution does the first thread take
A helicoil insert assures that load distribution throughout the entire length of the thread
How much of a thread runout is required when inserting a helicoil
The hole for the insert should be drilled to the diameter and depth specified in tables supplied by the manufacturer, the depth being calculated from the fitted length of the insert, plus the thread runout, plus half a pitch gap at each end of the insert
When a helicoil is inserted, unless specified otherwise, how far should the outer coil be below the surface of the component
At least half a pitch
How would the tang of a helicoil insert be removed
The insertion key is used as a punch
On a blind hole, long round nose pliers are required to bend the tang backwards and forwards until it fractures
When and how would a helicoil insert be removed
Under normal circumstances, particularly when fitting instructions are been carefully carried out he removal of inserts should be unnecessary. However if the insert has to be removed due to damage or wear, this can be done by bending the top coil inwards to form a rough tang and wound out using the insertion tool or pair of pliers
What is safetying with regard to fasteners
Safetying is the process of securing all aircraft bolts, nuts, screws and pins so they do not work loose due to vibration
What are the most common ways of safetying on aircraft
- Wire locking
- Cotter pins (split pins)
- Lock washers
- Locking plates
- Snap rings
- Self locking nuts
What are the two wirelocking methods used on aircraft
Single or double twist
What is the most common way of wire locking
Double twist
Where would single twist wire locking be used
On small screws, in a closely spaced closed geometrical pattern, on parts in electrical systems and in places that are extremely difficult to reach
What does the number of twists when wire locking depend on
The gauge of the wire and the AMM
What is the purpose of a pip pin
This is a simple and secure non threaded fastener allowing for rapid installation and removal of parts with out tooling
What 4 principle parts does a cam lock consist of
- Receptsble
- Grommet
- Retaining ring
- Stud assembly
Where would lightweight cam locks be used
Normally used on internal lightly loaded access panels
What are the two types of dzues fasteners available
Light duty and heavy duty
Where would light duty dzeus fasteners be used
Used on box covers, access hole covers and lightweight fairings
What two types of airlock fastener are available and what are they similar to
- Fixed type
- Floating type
Similar to a camlock
What are cotter pins made from
Low carbon steel, some others are made from CRES
If a cotter pin has one short leg where is it measured from
The shorter leg
What is a key
Name given to a specially shaped piece of metal that is used to transmit a drive at a considerable mechanical power from a shaft to a hub
What is a taper key
The agreed engineering standard is for a taper of 1 part in 100 on the thickness, with the tapering surface of the key matching the recess (or keyway cut in to the bore of the hub)
What is a hollow saddle key
This type is hollowed to fit the radius of the shaft. When driven in to position, its taper provides a friction drive between hub and shaft that is capable of transmitting a moderate load. There is no keyway cut in to the shaft and therefore hollow keys are not suitable for heavy loads
What type of keyway is not suitable for heavy loads
Hollow keys
What is a flat saddle key
This rectangular or square section key is driven in to a keyway in the hub and bears upon a flat on the shaft. It provides a more positive drive than that achieved by a hollow saddle key
What is a hub headed key
This taper key is fitted in to key ways which are machined partly in the shaft and partly in the hub. An important feature of fitting keys in to these key ways is that the key ways must be perfectly aligned before fitting the key. With this in mind it may be necessary to salve the key when assembling the parts together.
Capable of transmitting much greater loads than saddle keys
What is a feather key
This type of key is used when axial movement is required between the hub and the shaft. An example of the use of a feather key is when a gear in a pulley must slide along a shaft whilst continuing to transmit drive. The keyway in the hub is cut to allow the key minimum slide and top clearance needed to provide a sliding fit
What is a woodruf key
This key is made in to the shape of a segment of a parallel sided disk similar to he capital letter D. It fits in to a shaped cavity in the shaft which conforms closely to the profile of the key and in to a uniform keyway in the hub to provide a push fit on the sides with clearance along the top flat face of the key.
What is the advantage of the woodruff key
Suitable for fitting to parallel or tapered shafts
Rivets made from 1100 US material are used in what condition
‘As fabricated’
They are used to attach aluminium alloy components where a low strength rivet is sufficient to hold the load
What is done to US material 2017, 2117 and 7050 rivets
They are heat treated by the manufacturer, no further treatment is necessary.
They are used to attach aluminium alloy components where a medium strength is necessary
When are rivets made of US material 2024 supplied in T4 condition used
When high strength is required
What are Monel rivets
Monel rivets, with out heat treatment before use, are used in steel, titanium or aluminium alloy riveted assemblies
What are the characteristics of titanium rivets
Titanium rivets are rivets with a cylindrical or a partly tapered shank. No heat treatment is necessary for this type of rivet
What is a commonly used rule of thumb for selecting rivets
Choose a rivet whose diameter is at least 3 times the thickness of the thickest sheet being joined
Where would 1100 Aluminium rivets be suitable for
As it is commercially pure aluminium they are not suitable for structural applications on aircraft (too soft).
Used for non structural use only
Where would 2117 Aluminium alloy (AD) be suitable for
Sufficient strength for aircraft structure
Do not need to be heat treated
Driven from the bad in the condition received
AD = Small dimple on head!
Where would 2017 Aluminium alloy (D) rivets be suitable to be used
D rivets = Raised dot in centre of head!
Do not shave shear rivets
Where would 2024 Aluminium alloy (DD) rivets be suitable to be used
DD = Two raised dashes on the head
Made from heat treated Aluminium alloy
Placed in cold storage (-10) immediately after heat treating to prevent from being too hard to drive
High strength
Where would 5056 Aluminium alloy (B) rivets be used
B rivets = Raised cross on head
Used for attaching magnesium as the contain around 5% magnesium
Where would Corrosion resistant steel (F) rivets be used
Used for attaching corrosion resistant steel sheets
No marking on head
Used for applications such as exhaust shrouds
Where would Monel (M) rivets be used
Nikel alloy
Two recessed dimples or raised r
Can replace cres rivets
Where would titanium (T)rivets be used
Identified by a raised V or T
Used for attaching steel alloy to aluminium alloy
When pin (threaded) fasteners are used to join structure with outer surfaces that are not parralel what conditions are applicable
- Standard Aluminium collars are used in an out of parralel condition up to 3° is acceptable
- When standard cres collars are used in an out of parallel condition up to 0.5° is acceptable
What type of holes are pins for hi loks fitted
Interference holes
Unless made of steel, CRES or titanium then a clearance hole may be used
What must be ensured before fitting hi loks
- All pins and collars are correct type
- Made of correct material
- Surface protection intact
- Correct grip length
What is the difference between hi lock and hi lite
Hi hite 15% lighter
Slightly shorter (1 pitch run out instead of 2)
When would taper locks be used
In areas of the structure where high fatigue performance is required
What is the ratio between the taper lock and the hole it fits in to
1 in 48
How can taper locks be installed
By hand or by the use of power tools
What is a lock bolt
A lock bolt is a 2 piece assembly consisting of a pin and a collar which is swaged on to the locking groves on the pin shank to secure the pin when it is installed
What material lock bolts are the only ones permitted for repairs
CRES or titanium
What must be done temporarily before installing lock bolts
They must be secured with grip pins to ensure a tight fixture when fastened
If a lock bolt cannot be used due to limitations, what can be used in its place
A hi lok is an acceptable alternative
What are the 3 procedures of installing lock bolts
- Interference or transition fit in any structure
- Clearance fit in thin structure
- Clearance fit in thick structure
What are the 3 types of blind rivet used for repair work on aircraft
- Standard cherrylock
- Bulbed cherrylock
- Oversize cherrylock
What are the 3 parts that make up a blind rivet
- A tubular body with a head at one end
- A pin that goes through the body
- A lock cooler on the pin
Nearly every rivet has a layer of lubrication on it.what must not be done to this layer of lubrication
Remove or replace it, it must be left as it came
When you install a blind rivet a portion of the broken shank can protrude out of the top of the head. What can be done to rectify this
The excess sticking out can be milled
Where are bulged cherrylock rivets used
Particularly in double dimple or high vibration areas. Also fitted in thin sheet materials
When would oversize cherry locks be used
Designed to be used when a hole has been enlarged due to vibration and is not possible to go to the next diameter
Available in 1/64 oversize for each normal diameter size
What are the two types of blind rivet that can be used on aircraft repairs
- Cherrymax
- Oversize cherry max
What must be done to tucker pop rivets if they are used on external fuselage
The heads must be sealed to prevent ingress of dirt
What are the two different types of tucker of pop rivet
Break head (BH) Break stem (BS)
What material are pop rivets usually made from
Aluminium alloy or cadmium plated Monel with dome heads or 100° and 120° countersunk heads
What two types of avdels are available
Snap head and 100° and 120° countersunk
What is used to check avdel plug security
A pin tester
How are avdels installed
They are installed with a manually operated tool (avdel pliers) or by using an avdel riveter
Why would MBC cherrys be used over avdels
Avdels require cropping and milling
What are the characteristics of an MBC rivet
- Simple and versatile
- Lightweight and high strength
- Available in Aluminium alloy and stainless steel
What are Olympic lock rivets
A 3 piece mechanically locked, spindle type blind fastener.
What must never be done to an Olympic lock fastener
Never file the stem of an Olympic lock fastener it will weaken the mechanical lock
What 3 head styles are the Olympic lock fasteners available in
- Universal (protruding)
- 100° flush countersunk
- 100°flush shear
How can Olympic lock rivets be installed
As with Huck and cherry lock fasteners, although nearly identical in shape they can only be installed using their own tooling
What is a rivnut
A combination of a rivet and a nut
Necessary to attach anything with a screw to thin sheet metal
How is a rivnut fitted
A hole is drilled through the skin and the rivnut is slipped in to the hole and upset with a special puller so that it grips to the skin
When the installation tool is unscrewed, it leaves the threaded receptacle in the skin
