AME Structures

Solid Rivet Identification

We've all seen the articles floating around about the 1.8 million fasteners required to build the

DC-10's and 747's and other mega-aircraft. We know the importance of the lowly aircraft rivet;

now let's take a closer look at the details surrounding these myriad little items.

Aircraft rivets are identified by the marks on the manufacturer's head, and the alloys are

represented by a letter (or letters) in the part number.

Rivets with no head markings are soft 1100 (pure) aluminum, and not used in structural

applications. "B" rivets, alloyed with magnesium is identified with a cross on its head. The most

common rivet for AME's is the "AD" rivet with a single dimple in its head, which can be

installed without any additional handling. This makes the center of the rivet easier to locate when

drilling off the head. Double-dimples on the head (and a heavy silver color) will indicate a monel

rivet, usually found in high strength locations or in firewalls where temperature may be a

consideration. "D" and "DD" rivets are commonly called icebox rivets because they must be heat

treated before use. Following heat treating they must be kept in a freezer for no longer than 20

minutes prior to driving.

Aviation rivets are available in 4 common head styles, with the most popular being the AN470

Universal head and the AN426 100° Countersunk head.

Note that countersunk rivets, when defining length, include the head. Universal head rivet length

defines the shank only, not including the head.

Countersunk rivets are primarily installed as a low-drag fastener, but the pricetag for the extra

labour required is significant. If the tapered walls for the head of the countersunk rivet has been

made by a machine countersinking bit, then material has been removed which will cause a loss in

strength. If a dimpling operation was used, then strength is retained, however removing rivets

from a dimpled installation can be more time consuming and cause more damage. Of the rivets

discussed here, the universal head is the strongest general purpose rivet. One other style of

countersunk rivet, the NAS 1097, is discussed further down this page.

The MS or AN part number defines the rivet head style, and includes details such as the material

(code letters), diameter in 32's of an inch, and length in 16ths of an inch. Some aviation

companies purchase optional half-length sizes for their sheet metal technicians. Shank lengths

are established as in the diagram:

An example part number is:

AN426DD3 - 5

This part number calls out a 100° countersunk head rivet made of 2024 aluminum alloy, 3/32" in

diameter and 5/16" in length.

A rule of thumb for repair of aircraft structure states that AME's should use the same size and

head style of rivet as seen in nearby structure. If this is not available, consult the manufacturer's

structural repair manual (SRM). Generally, the choice is simplified to universal head or

countersunk head AD 2117 rivets.

In selecting the diameter of the rivet, use a guideline of at least 3 (three) times the thickness of

the thickest sheet. If the repair is being made to an existing aircraft structure, it is common

practice to use the same diameter of rivets in adjacent fasteners, preferrably referring to rows

inboard or forward on the fuselage. Length is gauged by using the formula of 1.5 times the

diameter protruding through the structure. That is to say, if we are riveting two skins of 0.040",

then our rivet diameter would be at least 0.120" (or 1/8"), and the length would be estimated at

0.267". We can calculate this length by adding the two skins (.040 x 2) to the diameter-and-a-

half of the rivet (0.187") to achieve a length of 0.267". The nearest size to this length is a 1/4"

grip length rivet (a -4).

After driving the solid rivet, we should inspect the shop head (also called the "formed" head) for

dimensions of .5 x D in height, and 1.5 x D in width.

NAS 1097 rivets are a reduced-head countersunk rivet, manufactured in similar materials to the

AN426 series. The head size of the 1097 is half the width of the 426, yet retains the 100° head

angle. 1097's are not used in tension applications for this reason, but they can be found in smaller

skin thickness areas. 1097's are not as widely used as regular AN426 rivets.

NAS 523 Rivet Code

In certain aviation companies the use of the NAS523 rivet identification code is used on

diagrams and drawings. The code embodies a number of details about the rivets to be used in a

single 4-cornered symbol, with a "crosshair" at the center. Each quadrant is given a compass

designation: NW for northwest, NE for northeast, SW for southwest and SE for southeast. These

compass designations are not shown on the code, only the details.

In the symbol, the upper left NW corner contains the rivet part number in either AN or MS part

numbers, and a rivet material designation. For example, the letters BJ identify a standard

MS20470AD rivet, which is made from 2117 alloy.

The NE quadrant indicates rivet diameter, and the location of the manufacturers head (Near or

Far).

The SW quandrant indicates what special methods should be applied to the fasteners, such as

dimpling or countersinking. For example, D stands for Dimpling, D2 stands for Dimple both

sheets, and D2C means Dimple two top sheets and countersink the third.

The lower right corner specifies fastener length in 1/16" increments. Example: a 3/8" rivet is

shown as a -6.

See the NAS523 Rivet Code sheets for full details.

Solid rivets

Sophisticated riveted joint on a railway bridge

Rivets are a permanent mechanical fastener. Before being installed a rivet consists of a smooth

cylindrical shaft with a head on one end. The end opposite the head is called the buck-tail. On

installation the rivet is placed in a punched or drilled hole, and the tail is upset, or bucked (i.e.,

deformed), so that it expands to about 1.5 times the original shaft diameter, holding the rivet in

place. To distinguish between the two ends of the rivet, the original head is called the factory

head and the deformed end is called the shop head or buck-tail.

Because there is effectively a head on each end of an installed rivet, it can support tension loads

(loads parallel to the axis of the shaft); however, it is much more capable of supporting shear

loads (loads perpendicular to the axis of the shaft). Bolts and screws are better suited for tension

applications.

Fastenings used in traditional wooden boat building, such as copper nails and clinch bolts, work

on the same principle as the rivet but were in use long before the term rivet was introduced and,

where they are remembered, are usually classified among the nails and bolts respectively.

Types[edit]

There are a number of types of rivets, designed to meet different cost, accessibility, and strength

requirements:

Solid/round head rivets[edit]

A typical technical drawing of a universal head solid rivet

Solid rivets are one of the oldest and most reliable types of fasteners, having been found in

archaeological findings dating back to the Bronze Age. Solid rivets consist simply of a shaft and

head that are deformed with a hammer or rivet gun. A rivet compression or crimping tool can

also deform this type of rivet. This tool is mainly used on rivets close to the edge of the fastened

material, since the tool is limited by the depth of its frame. A rivet compression tool does not

require two people, and is generally the most foolproof way to install solid rivets.

Riveting team working on the cockpit shell of a C-47 transport at the plant of North American Aviation.

The woman on the left operates an air hammer, while the man on the right holds a bucking bar

Solid rivets are used in applications where reliability and safety count. A typical application for

solid rivets can be found within the structural parts of aircraft. Hundreds of thousands of solid

rivets are used to assemble the frame of a modern aircraft. Such rivets come with rounded

(universal) or 100° countersunk heads. Typical materials for aircraft rivets are aluminium alloys

(2017, 2024, 2117, 7050, 5056, 55000, V-65), titanium, and nickel-based alloys (e.g., Monel).

Some aluminum alloy rivets are too hard to buck and must be softened by annealing prior to

being bucked. "Ice box" aluminum alloy rivets harden with age, and must likewise be annealed

and then kept at sub-freezing temperatures (hence the name "ice box") to slow the age-hardening

process. Steel rivets can be found in static structures such as bridges, cranes, and building

frames.

The setting of these fasteners requires access to both sides of a structure. Solid rivets are driven

using a hydraulically, pneumatically, or electromagnetically driven squeezing tool or even a

handheld hammer. Applications where only one side is accessible require blind rivets.

High-strength structural steel rivets[edit]

Structural steel rivets like this one were used in the construction of the Golden Gate Bridge in the 1930s.

Until relatively recently, structural steel connections were either welded or riveted. High-strength

bolts have largely replaced structural steel rivets. Indeed, the latest steel construction

specifications published by AISC (the 14th Edition) no longer covers their installation. The

reason for the change is primarily due to the expense of skilled workers required to install high

strength structural steel rivets. Whereas two relatively unskilled workers can install and tighten

high strength bolts, it takes a minimum of four highly skilled riveters to install rivets in one joint

at a time.[citation needed]

At a central location near the areas being riveted, a furnace was set up. Rivets were placed in the

furnace and heated to a glowing hot temperature. The Rivet warmer or heater used tongs to

individually remove rivets and throw them to a catcher stationed near the joints to be riveted.

The catcher usually caught the rivet in a leather bucket with an ash lined bottom then placed the

glowing hot rivet into the hole to be riveted, and quickly turned around to await the next rivet.

The "Holder up or holder on" would then hold a heavy rivet set or dolly or another (larger)

pnuematic hammer against the round head of the rivet, while the Riveter (or sometimes two

riveters)applied a pneumatic rivet hammer to the unformed head, making it mushroom tightly

against the joint in its final domed shape. Upon cooling, the rivet contracted and exerted further

force, tightening the joint.

The last commonly used high strength structural steel rivets were designated ASTM A502 Grade

1 rivets.[1]

Such riveted structures may be insufficient to resist seismic loading from earthquakes if the

structure was not engineered for such forces, a common problem of older steel bridges. This is

due to the fact that a hot rivet cannot be properly heat treated to add strength and hardness. In the

seismic retrofit of such structures it is common practice to remove critical rivets with an oxygen

torch, precision ream the hole, and then insert a machined and heat treated bolt.

Semi-tubular rivets[edit]

A typical technical drawing of an oval head semi-tubular rivet

Semi-tubular rivets (also known as tubular rivets) are similar to solid rivets, except they have a

partial hole (opposite the head) at the tip. The purpose of this hole is to reduce the amount of

force needed for application by rolling the tubular portion outward. The force needed to apply a

semitubular rivet is about 1/4 of the amount needed to apply a solid rivet. Tubular rivets can also

be used as pivot points (a joint where movement is preferred) since the swelling of the rivet is

only at the tail. Solid rivets expand radially and generally fill the hole limiting movement. The

type of equipment used to apply semi-tubular rivets range from prototyping tools (less than $50)

to fully automated systems. Typical installation tools (from lowest to highest price) are hand set,

manual squeezer, pneumatic squeezer, kick press, impact riveter, and finally PLC-controlled

robotics. The most common machine is the impact riveter and the most common use of

semitubular rivets is in lighting, brakes, ladders, binders, HVAC duct work, mechanical

products, and electronics. They are offered from 1/16-inch (1.6 mm) to 3/8-inch (9.5 mm) in

diameter (other sizes are considered highly special) and can be up to 8 inches (203 mm) long. A

wide variety of materials and platings are available, most common base metals are steel, brass,

copper, stainless, aluminum and most common platings are zinc, nickel, brass, tin. Tubular rivets

are normally waxed to facilitate proper assembly. An installed tubular rivet has a head on one

side, with a rolled over and exposed shallow blind hole on the other. Semi-tubular rivets are the

fastest way to rivet in mass production, but require capital investment.

Blind rivets[edit]

Three aluminium blind rivets: 1/8", 3/32", and 1/16"

Blind rivets, commonly referred to as pop rivets (POP was a brand name of the original blind

rivet manufacturer, now owned by Emhart Teknologies) are tubular and are supplied with a

mandrel through the center. The rivet assembly is inserted into a hole drilled through the parts to

be joined and a specially designed tool is used to draw the mandrel into the rivet. This expands

the blind end of the rivet and then the mandrel snaps off. These types of blind rivets have non-

locking mandrels and are sometimes avoided for critical structural joints because the mandrels

may fall out, due to vibration or other reasons, leaving a hollow rivet that has a significantly

lower load carrying capability than solid rivets. Furthermore, because of the mandrel they are

more prone to failure from corrosion and vibration. Unlike solid rivets, blind rivets can be

inserted and fully installed in a joint from only one side of a part or structure, "blind" to the

opposite side.[2]

Prior to the adoption of blind rivets, installation of a solid rivet typically required access to both

sides of the assembly: a rivet hammer on one side and a bucking bar on the other side. In 1916

Royal Navy reservist and engineer Hamilton Neil Wylie filed a patent for an "improved means of

closing tubular rivets" (granted May 1917).[3]

In 1922 Wylie joined the British aircraft

manufacturer Armstrong-Whitworth Ltd to advise on metal construction techniques; here he

continued to develop his rivet design with a further 1927 patent[4]

that incorporated the pull

through mandrel, and allowed the rivet to be used blind. By 1928, the George Tucker Eyelet

company produced a 'cup' rivet based on the design. It required a separate GKN mandrel and the

rivet body to be hand assembled prior to use for the building of the Siskin III aircraft. Together

with Armstrong-Whitworth, the Geo. Tucker Co. further modified the rivet design to produce a

one piece unit incorporating mandrel and rivet.[5]

This product was later developed in Aluminium

and trademarked as the 'POP' rivet. The United Shoe Machinery Co. produced the design in the

US as inventors such as Carl Cherry and Lou Huck experimented with other techniques for

expanding solid rivets.

Due to this feature, blind rivets are mainly used when access to the joint is only available from

one side. The rivet is placed in a drilled hole and is set by pulling the mandrel head into the rivet

body, expanding the rivet body and causing it to flare against the reverse side. As the head of the

mandrel reaches the face of the blind side material, the pulling force is resisted, and at a

predetermined force, the mandrel snaps at its break point, also called blind setting. A tight joint

formed by the rivet body remains, the head of the mandrel remains encapsulated at the blind side,

although variations of this are available, and the mandrel stem is ejected.

They are available in flat head, countersunk head, and modified flush head with standard

diameters of 1/8, 5/32 and 3/16 inch. Blind rivets are made from soft aluminum alloy, steel

(including stainless steel), copper, and Monel.

There are also structural blind rivets, which are designed to take shear and tensile loads.[6]

The rivet body is normally manufactured using one of three methods:

Name Description

Wire the most common method

Tube common in longer lengths, not normally as strong as wire

Sheet least popular and generally the weakest option

There is a vast array of specialty blind rivets that are suited for high strength or plastic

applications. Typical types include:

Name Description

TriFold

a rivet that splits into three equal legs like a molly bolt. Typically used in soft plastics where

a wide footprint is needed at the rear surface. Used in automotive interiors and vinyl

fences. (See Oscar rivets.)

Structural

rivet(a)

an "external" mechanically locked structural blind rivet that is used where a watertight,

vibration resistant connection is of importance. Typically used in manufacture or repair of

truck bodies. A special nose piece is required to apply this rivet.

Structural

rivet(b)

an "internal" mechanically locked structural blind rivet that is used where a watertight,

vibration resistant connection is of importance. Typically used in manufacture or repair of

truck bodies.

Internally and externally locked structural blind rivets can be used in aircraft applications

because, unlike other types of blind rivets, the locked mandrels cannot fall out and are water

tight. Since the mandrel is locked into place they have the same or greater load carrying capacity

as solid rivets and may be used to replace solid rivets on all but the most critical stressed aircraft

structures.

The typical assembly process requires the operator to install the rivet in the nose of the tool by

hand then actuate the tool. However, in recent years automated riveting systems have become

popular in an effort to reduce assembly costs and repetitive disorders. The cost of such tools

range from US$1,500 for autofeed pneumatics to US$50,000 for fully robotic systems.

Oscar rivets[edit]

Oscar Rivet shown with mandrel. (Dashed lines depict flare/flange after installation.)

Oscar rivets are similar to blind rivets in appearance and installation, but have splits (typically

three) along the hollow shaft. These splits cause the shaft to fold and flare out (similar to the

wings on a toggle bolt's nut) as the mandrel is drawn into the rivet. This flare (or flange) provides

a wide bearing surface that reduces the chance of rivet pull-out. This design is ideal for high

vibration applications where the back surface is inaccessible

Drive rivet[edit]

A drive rivet is a form of blind rivet that has a short mandrel protruding from the head that is

driven in with a hammer to flare out the end inserted in the hole. This is commonly used to rivet

wood panels into place since the hole does not need to be drilled all the way through the panel,

producing an aesthetically pleasing appearance. They can also be used with plastic, metal, and

other materials and require no special setting tool other than a hammer and possibly a backing

block (steel or some other dense material) placed behind the location of the rivet while

hammering it into place. Drive rivets have less clamping force than most other rivets. Drive

screws, possibly another name for drive rivets, are commonly used to hold nameplates into blind

holes. They typically have spiral threads that grip the side of the hole. [7]

Flush rivet[edit]

A flush rivet is used primarily on external metal surfaces where good appearance and the

elimination of unnecessary aerodynamic drag are important. A flush rivet takes advantage of a

countersink hole; they are also commonly referred to as countersunk rivets. Countersunk or flush

rivets are used extensively on the exterior of aircraft for aerodynamic reasons. Additional post-

installation machining may be performed to perfect the airflow.

Friction-lock rivet[edit]

These resemble an expanding bolt except the shaft snaps below the surface when the tension is

sufficient. The blind end may be either countersunk ('flush') or dome shaped.

One early form of blind rivet that was the first to be widely used for aircraft construction and

repair was the Cherry friction-lock rivet. Originally, Cherry friction-locks were available in two

styles, hollow shank pull-through and self-plugging types. The pull-through type is no longer

common, however, the self -plugging Cherry friction-lock rivet is still used for repairing light

aircraft.

Cherry friction-lock rivets are available in two head styles, universal and 100 degree

countersunk. Furthermore, they are usually supplied in three standard diameters, 1/8, 5/32 and

3/16 inch.

A friction-lock rivet cannot replace a solid shank rivet, size for size. When a friction-lock is used

to replace a solid shank rivet, it must be at least one size larger in diameter because the friction-

lock rivet loses considerable strength if its center stem falls out due to vibrations or damage.

Rivet alloys, shear strengths, and driving condition[edit]

Alloy type Alphabetical letter Driven condition Marking on head

1100 A 1100-F PLAIN

2117 AD 2117T3 DIMPLE

5056 B 5056H32 RAISED CROSS

2017 D 2017T31 RAISED DOT

2024 DD 2024T31 TWO RAISED DASHES

7050 E 7050T73 RAISED RING

Self-pierce rivets[edit]

Self-pierce riveting (SPR) is a process of joining two or more materials using an engineered

rivet. Unlike solid, blind and semi-tubular rivets, self-pierce rivets do not require a drilled or

punched hole.

SPRs are cold forged to a semi-tubular shape and contain a partial hole to the opposite end of the

head. The end geometry of the rivet has a chamfered poke that helps the rivet pierce the materials

being joined, a hydraulic or electric servo rivet setter drives the rivet into the material, and an

upsetting die provides a cavity for the displaced bottom sheet material to flow.

The self-pierce rivet fully pierces the top sheet material(s) but only partially pierces the bottom

sheet. As the tail end of the rivet does not break through the bottom sheet it provides a water or

gas tight joint. With the influence of the upsetting die, the tail end of the rivet flares and

interlocks into the bottom sheet forming a low profile button.

Rivets need to be harder than the materials being joined, they are heat treated to various levels of

hardness depending on the materials ductility and hardness. Rivets come in a range of diameters

and lengths depending on the materials being joined, head styles are either flush countersunk or

pan heads.

Depending on the rivet setter configuration, i.e. hydraulic, servo, stroke, nose-to-die gap, feed

system etc., cycle times can be as quick as one second. Rivets are typically fed to the rivet setter

nose from tape and come in cassette or spool form for continuous production.

Riveting systems can be manual or automated depending on the application requirements; all

systems are very flexible in terms of product design and ease of integration into a manufacturing

process.

SPR joins a range of dissimilar materials such as steel, aluminum, plastics, composites and pre-

coated or pre-painted materials. Benefits include low energy demands, no heat, fumes, sparks or

waste and very repeatable quality.

Sizes[edit]

Installing rivets on M3 tank hull

Because the Industrial Revolution occurred first in Britain (where the standards of the Roman

Empire persisted in British Standards) these dimensions are still widely used, and may persist,

particularly in former British colonies including, most notably,the USA.

Although there are a plethora of specifications, most rivets come in two basic flavours:

Imperial units (fractions of inches) with diameters such as 1/8" (3.175mm) or 5/16" (7.938mm). Système international or SI units with more readily understood diameters such as such as 3mm,

8mm, and these have been adopted in Europe and in many emerging countries.

The main official standards relate more to technical parameters such as ultimate tensile strength

and surface finishing than physical length and diameter. They are:

Abbreviation Issuing authority

AIA / NASM Aerospace Industries Association (AIA) Imperial Standard, NASM is an acronym for

National Aerospace Standards, MIL-STD.

AN / MS United States Military Standard used by the USA army, navy, or air force is Imperial.

ASME / ANSI The American Society of Mechanical Engineers (ASME) 18-digit PIN code Imperial system is

approved by ANSI and adopted by the U.S. Department of Defense.

BS /BSI British Standards Institution. provides four-figure BS numbers for Imperial standards and

also provides similar BS numbers for official translations into English for the Internal

market of the of European Union (see below: DIN or SI)

SAE The Society of Motor Engineers is a worldwide organization that provides (mostly Imperial)

specifications for design and testing for components used in the automotive industry.

JIS

Japanese Industrial Standard (JIS) is a metric system largely based on DIN with some minor

modifications to meet the needs of the Japanese market, nortably used in Japanese

electronic equipment.

DIN

Deutsches Institut für Normung is the German national metric standard used in most

European countries because it closely resembles the newer International Standards

Organizations (ISO) specifications. DIN fasteners use a DIN style identifier plus the material

and the finish or plating (if any).

ISO

International Organization for Standardization (ISO) is a worldwide metric standard.

Clarified ISO standards for (metric) fasteners are rapidly gaining international recognition

in preference to the similar DIN, on which SI was originally based.

Imperial[edit]

Rivet diameters are commonly measured in 1⁄32-inch increments

[8] and their lengths in

1⁄16-inch

increments, expressed as "dash numbers" at the end of the rivet identification number. A "dash 3

dash 4" (XXXXXX-3-4) designation indicates a 3⁄32-inch diameter and

4⁄16-inch (or

1⁄4-inch)

length. Some rivets lengths are also available in half sizes, and have a dash number such as –3.5

(7⁄32 inch) to indicate they are half-size. The letters and digits in a rivet's identification number

that precede its dash numbers indicate the specification under which the rivet was manufactured

and the head style. On many rivets, a size in 32nds may be stamped on the rivet head. Other

makings on the rivet head, such as small raised or depressed dimples or small raised bars indicate

the rivet's alloy.

To become a proper fastener, a rivet should be placed in hole ideally 4–6 thousandths of an inch

larger in diameter. This allows the rivet to be easily and fully inserted, then setting allows the

rivet to expand, tightly filling the gap and maximizing strength.

Metric[edit]

Rivet diameters and lengths are measured in millimeters. Conveniently, the rivet diameter relates

to the drill required to make a hole to accept the rivet, rather than the actual diameter of the rivet,

which is slightly smaller. This facilitates the use of a simple drill-gauge to check both rivet and

drill are compatible. For general use, diameters between 2mm - 20mm and lengths from 5mm -

50mm are common. The design-type, material and any finish is usually expressed in plain

language (often English).

Applications[edit]

A riveted buffer beam on a steam locomotive

A riveted truss bridge over the Orange River

Detail of a 1941 riveted ship hull, with the rivets clearly visible

Manual installation of a solid rivet

Impact method for solid rivet and semi tubular rivets

Before welding techniques and bolted joints were developed, metal framed buildings and

structures such as the Eiffel Tower, Shukhov Tower and the Sydney Harbour Bridge were

generally held together by riveting. Also automobile chassis were riveted. Riveting is still widely

used in applications where light weight and high strength are critical, such as in an aircraft. Many

sheet-metal alloys are preferably not welded as deformation and modification of material

properties can occur.

Rivets were also used in many tanks during World War II by a large number of countries.

However, many countries soon learned that rivets were a large weakness in tank design, since if

a tank was hit by a large projectile it would dislocate the rivets and they would fly around the

inside of the tank and injure or kill the crew, even if the projectile didn't penetrate the armor.

Some countries such as Italy, Japan, and Britain used rivets in some or all of their tank designs

throughout the war for various reasons, such as lack of welding equipment or inability to weld

very thick plates of armor effectively.

Blind rivets are used almost universally in the construction of plywood road cases.

Common but more exotic uses of rivets are to reinforce jeans and to produce the distinctive

sound of a sizzle cymbal.

Joint analysis[edit]

The stress and shear in a rivet is analyzed like a bolted joint. However, it is not wise to combine

rivets with bolts and screws in the same joint. Rivets fill the hole where they are installed to

establish a very tight fit (often called interference fit). It is difficult or impossible to obtain such a

tight fit with other fasteners. The result is that rivets in the same joint with loose fasteners carry

more of the load—they are effectively more stiff. The rivet can then fail before it can redistribute

load to the other loose fit fasteners like bolts and screws. This often causes catastrophic failure of

the joint when the fasteners unzip. In general, a joint composed of similar fasteners is the most

efficient because all fasteners reach capacity simultaneously.

Installation[edit]

Solid and semi tubular rivets[edit]

There are several methods for installing solid rivets.

Manual with hammer and handset or bucking bar Pneumatic hammers Handheld squeezers Riveting machines Pin hammer, rivet set

Rivets small enough and soft enough are often bucked.[9]

In this process the installer places a

rivet gun against the factory head and holds a bucking bar against the tail or a hard working

surface. The bucking bar is a specially shaped solid block of metal. The rivet gun provides a

series of high-impulse forces that upsets and work hardens the tail of the rivet between the work

and the inertia of the bucking bar. Rivets that are large or hard may be more easily installed by

squeezing instead. In this process a tool in contact with each end of the rivet clinches to deform

the rivet.

Rivets may also be upset by hand, using a ball-peen hammer. The head is placed in a special hole

made to accommodate it, known as a rivet-set. The hammer is applied to the buck-tail of the

rivet, rolling an edge so that it is flush against the material.

Testing[edit]

Solid rivets for construction[edit]

A hammer is also used to "ring" an installed rivet, as a non-destructive test for tightness and

imperfections. The inspector taps the head (usually the factory head) of the rivet with the

hammer while touching the rivet and base plate lightly with the other hand and judges the quality

of the audibly returned sound and the feel of the sound traveling through the metal to the

operator's fingers. A rivet tightly set in its hole returns a clean and clear ring, while a loose rivet

produces a recognizably different sound.

Testing of blind rivets[edit]

A blind rivet has strength properties that can be measured in terms of shear and tensile strength.

Occasionally rivets also undergo performance testing for other critical features, such as pushout

force, break load and salt spray resistance. A standardized destructive test according to the Inch

Fastener Standards is widely accepted[10][11]

The shear test involves installing a rivet into two plates at specified hardness and thickness and

measuring the force necessary to shear the plates. The tensile test is basically the same, except

that it measures the pullout strength. Per the IFI-135 standard, all blind rivets produced must

meet this standard. These tests determine the strength of the rivet, and not the strength of the

assembly. To determine the strength of the assembly a user must consult an engineering guide or

the Machinery's Handbook[12]

Alternatives[edit] Bolted joints Brazing Clinching

Folded joints Nails Screws

Soldering Welding

See also[edit]

Cleko Clinker (boat building) Rivet nut Rosie the Riveter

References[edit]

1. Jump up ^ Segui, William T. (2007). Steel Design (4th ed.). Toronto: Thomson. ISBN 0-495-24471-6.

2. Jump up ^ Blind Rivets, August 1942, Popular Science early article that explains how they work 3. Jump up ^ Improved means of closing tubular rivets. - United Kingdom Patent GB106169 4. Jump up ^ Improvements in and relating to rivets and riveting - United Kingdom Patent

GB286471 5. Jump up ^ Emhart News June 2011 GB 6. Jump up ^ Smith 1990, p. 159. 7. Jump up ^ . Hanson Rivet http://www.hansonrivet.com/w58.htm. Retrieved 18 April 2013.

Missing or empty |title= (help) 8. Jump up ^ http://machinedesign.com/article/straight-facts-on-blind-rivets-0316 9. Jump up ^ The term bucked comes from a name for one of the two parts of a rivet. The head of

the rivet is one part, and is the part that the air-hammer strikes. The other part is referred to as the bucktail, and is the part that the bucking bar is held against. Hence the terms bucking bar, bucked, and buck-man.

10. Jump up ^ "Industrial Fasteners Institute". Industrial-fasteners.org. Retrieved 2012-04-28. 11. Jump up ^ IFI, Industrial Fasteners Institure (2003). Inch Fastener Standards (7th ed.). Industrial

Fasteners Institure: Industrial Fasteners Institure. ISBN unknown Check |isbn= value (help). 12. Jump up ^ Heald, Oberg, Jones, Ryffel, McCauley and Heald (2008). Machinery's Handbook (28th

ed.). Industrial Press: Industrial Press. ISBN 0-8311-2828-3.

Bibliography[edit]

Smith, Carroll (1990). Carroll Smith's Nuts, Bolts, Fasteners, and Plumbing Handbook. MotorBooks/MBI Publishing Company. p. 112. ISBN 0-87938-406-9.

Popular Science, November 1941, Self-Setting Explosive Rivet Speeds Warplane Building system used by both the US and Germany in World War Two for aircraft assembly - see bottom half of page

"Four Methods of Flush Riveting" film made by Disney Studios during World War Two "Hold Everything", February 1946, Popular Science new rivet types developed during World War

Two "Blind Rivets they get it all together. Popular Science, October 1975, pp. 126–128.

Kev’s AME Structures

Something to note about the following material:

What you see here is the text taken from the power point presentations seen in class. There is much redundancy, and there's lots of material which is missed because the images are not copied here for lack of web space. Furthermore, every time this material is taught, it changes a little, and those changes won't be reflected here. This web page is offered to save students time during lecture.

AVAM2102

Aircraft Structures

• Aircraft Construction

• Stresses and Loads

• Basic Math

• Drill Bits

• Heat Treating

• Rivet Styles

Aircraft Structures

• Rivet Diameters and Lengths

• Rivet materials

• Clecos

• Cherry Rivets

• Rivet Layout Patterns

• Tools

• Riveting

Aircraft Structures

• Removing Rivets

• Sheet Metal Stock

• Bending and forming

• Methods of countersinking

Before we begin…

• In order to keep our sheet metal usage within reasonable limits, we must

utilize all available materials. For practicing drilling, countersinking, riveting, or

any other new process or tool, we use small offcuts of metal which would

otherwise be wasted. Any pieces which are not 10 square inches in area will be

recycled, otherwise we use them for practice or small projects.

Trusses

• Rectangular or triangular

• Often fabric covered

• Warren or Pratt types

Monocoque Construction:

• Derives strength from the formed skin

• Similar to eggshell construction

• No internal bracing required

Semi-Monocoque

• Uses framework rings, stringers, ribs, formers, frames, clips, gussets.

• More complicated, but also very repairable.

“Aircraft are generally designed to withstand 1.5 times their design limits”

Semi-Monocoque

• Longitudinal structural members of a semi-monocoque frame:

– Longerons

– Stringers

4 metals used in A/C construction:

• Aluminum (and alloys)

• Titanium (and alloys)

• Magnesium (and alloys)

• Steel (and alloys)

Stresses and Loads

• Stress: “internal resistance to an external load”

• Strain: “measure of deformation caused by a load being applied”

Stresses and Loads

• Fasteners are best used in Shear loading

• 5 main stresses:

– Shear

– Tension

– Compression

– Torque

– Bending

Stresses and Loads

• The prime consideration of our sheet metal repairs must always be returning

the original shear strength of the riveted joint.

• Fasteners may be placed in single shear (a lap joint), or in double shear

(multiple sheets joined) configuration.

Stresses and Loads

• Joggles in a removed rivet shank indicate a Shear failure

Basic Math

• Be able to convert fractions into decimals

• Be able to read micrometers or vernier calipers

Measure in 1/100ths of an inch

• With practice, you can become quite accurate with a simple scale.

Basic Math

• In industry, dimensional (size) measurements are frequently given in decimals instead of halves, quarters, eighths or sixteenths of an inch, particularly in cases where work needs to be much more accurate than the common fraction can accomplish.

Basic Math

• The decimal point is the mark that tells us the difference between whole

numbers and parts of a whole number.

Basic Math

• Converting Common Fractions into Decimals

• This is the simplest process, sometimes required when handling standard MS

and NAS hardware (e.g., What is the exact decimal size of a 3/16 bolt?). The

result is achieved by dividing the "numerator" (top number) by the "denominator"

(bottom number).

Drill Bits

• 4 methods of incrementing:

– Number

– Letter

– Fractional

– Metric

Drill Bits

• Check whether you have split point drill bits, or regular.

Drill Bits

• Easy conversions: use chart in handbook (page 79 ??)

• Measure with vernier calipers lengthwise along the lands, NOT across the

flutes. Do not take the reading from the shank end.

• Or you can use a drill gauge plate

Drill Bits: Drill Gauge Plate

Drill Bits

• Included angles for bits:

– Stainless steel: 135°

• Low speed, high pressure

– Aluminum: 118°

• High speed, low pressure

Drill Bits

• Carbon Steel (dull black)

• High speed steel (shiny silver)

• Cobalt (shiny brown)

Drill Bit Sizes

• Installation and removal of rivets use different sizes

• To install a 1/8” solid rivet, drill a #30 hole. That is, drill a hole with a #30 drill

bit

• To remove that same rivet, use a 1/8” drill bit.

• Difference is only a few thousandths of an inch

• A 1/8” rivet will not fit into a 1/8” hole.

Drill Bit Sizes

• Common drill bit sizes for solid rivets:

– #40 installs 3/32” rivets

– #30 installs 1/8” rivets

– #21 installs 5/32” rivets

– #11 installs 3/16” rivets

Center punching

• An optional practice, depending on skill and tools available

• Center punching may not be required if you have sharp split point drill bits

• Center punching has a tendency to warp thin materials – use caution

Reamers

• Reamers:

– Used for extra accuracy of hole sizes

– Types: hand, machine, tapered, expanding, spiral, straight, etc.

– Do NOT turn a reamer backwards!

Heat Treating

• Aluminum alloys use a 4 number system:

– 1xxx pure aluminum

– 2xxx materials alloyed with copper

– 7xxx materials alloyed with zinc

Heat Treating

• Alloying elements:

– 1xxx Pure Aluminum

– 2xxx alloyed with Copper

– 3xxx alloyed with Manganese

– 4xxx alloyed with Silicon

– 5xxx alloyed with Magnesium

– 6xxx alloyed w. Magnesium & Silicon

– 7xxx alloyed with Zinc

Heat Treating

• Two types of aluminum alloys:

• Heat Treatable

– Can be both softened and hardened by heat

• Non-Heat Treatable

– Can be softened by heat, but not hardened

Heat Treating

• Pure aluminum alone has a low tensile strength: 13,000 psi.

• Mild carbon steel has 90,000 psi.

• Copper, Magnesium and Manganese added to form “Duralumin”, an early

aluminum alloy. 62,000 psi.

• Now alclads achieve 70 – 76,000 psi.

Heat Treating

• “O” material is very soft; flexes easily and does not return to original shape

• T3 Heat treated condition is “Heat Treated and Cold Worked”

• T4 condition is “Solution Heat treated only”

• Materials using “H” designation are rated on a hardness scale; different than

the heat treating scale (see page 2-10 in Jeppesen)

Heat Treating

• Hardness: “Property of a material that enables it to resist cutting, penetration,

and abrasion.”

• Artificial Aging is also called Precipitation Heat treating.

Heat Treating

• The vast majority of our AME work will use 2024 T3 of various thicknesses

Rivets

• (see page 2-37 in Jeppesen)

• Head Styles:

– Round head

– Flat Head

– Universal Head

– Countersunk Head

– 1097 Countersunk head

Rivets

• Most common is the Universal head rivet and the countersunk head rivet

• The AN or MS number of a rivet identifies the head shape, while the letters

identify the alloy in the rivet

Rivets

• Universal Head:

– AN470 or MS20470

• Countersunk Head:

– AN426 or MS20426

– NAS1097 (reduced countersunk head)

Rivets

• Why do we countersink?

– Decreases wind resistance

– But takes more time, more expensive

Rivets

• Rivet heads are countersunk 100°

• Material Thickness is the prime consideration. For example, the minimum

skin thickness for a countersunk 3/32” rivet is .040”. And .051” material is

required for a 1/8” rivet.

• Also watch for increased edge distance

• Length is measured by including the head

Rivets

• Solid rivets increment their diameters in 1/32’s of an inch

• Solid rivets increment their lengths in 1/16’s of an inch

• Some manufacturers supply half-dash length increments.

Rivets

• Diameter sample part numbers

• MS20470AD3 is:

– Universal head

– 2117 aluminum alloy (dimpled head marking)

– 3/32” diameter

– No length specified here

Rivets

• MS20470A4 is:

– Universal head

– 1100 Aluminum (no head marking)

– 1/8” diameter

– No length specified

Rivets

• NAS1097AD5 – 3 is:

– Reduced head countersunk rivet

– 2117 aluminum alloy (dimpled)

– 5/32” diameter

– 3/16” length

Rivets

• Identify this one:

• MS20470DD8 – 6

Rivets

• According to the chart what is a BB rivet?

• What is a BJ rivet?

Icebox Rivets

• Material is 2017 aluminum, or 2024 aluminum

• Must be heat treated before driving

• Condition will be preserved for a short period by refrigeration (retards the age

hardening process)

Other Materials

• Monel, as specified by an “M” in the part number

– Example: MS20470M4 – 4

– Used for firewall applications

– Hard to drive and remove

• Magnesium, made of 5056 material

Clecos

• Temporary holding device

• Relies on accurate sizing of holes in material

• Requires specialized pliers to install and remove

Clecos

• Common cleco sizes:

– 3/32” silver

– 1/8” brown

– 5/32” black

– 3/16” brass

– ¼” copper

QuikQuiz

• What is this rivet?

MS20470 AD 4 – 4

– What diameter?

– What length?

– What material?

– What cleco color?

– What size drill bit to install?

– What size drill bit to remove?

Sheet metal stock

• Cladding: a layer of pure aluminum (under the plastic) covering the alloy

material.

• 2024 T3 the most popular for aviation

• Sizes .016” through to plate sizes of .250”

• Material specification of 2024 T3 is QQ-A 250/5

• Grain is the same direction as the printing on the sheet

Sheet metal stock

• Deburr all edges, radius all corners

• Transfer any certification numbers to left-over materials

Casting & Forging

• Casting is a molten material poured into a mold

• Forging is a heated material pounded or squeezed into shapes

Chemical Milling

• Uses Sodium hydroxide or other alkaline solution to etch shapes into the

material

• Material must be at least .250” or less to chem-mill. (too expensive above

that)

• Material is masked, immersed in acid for a specified duration at a certain

temperature

• End of Slide Show 1

• Go to Slide Show 2; Tools

Kev’s AME Sheet Metal

Part III

Riveting, Layout, Removals

Rivet Patterns

• Rivet Pitch: distance between centers of rivets in the same row

• Distance between parallel rows should be 75% of the pitch. This is called the

Gage.

• Distance between rivets should be 6 – 8 diameters, in the same row

Rivet Patterns

• Proper rivet diameter should be 3x material thickness of the thickest sheet

• Layouts do not use leaded pencil, nor scribers, unless on a cut line.

• Absolute minimum pitch is 3D

• Edge distance is 2D – 4D for universal head

• ED is 2.5D – 4D for countersunk head

Edge Distance, Universal Head

Proper Rivet Length

• A proper length of a rivet, prior to driving, should show 1.5D protruding from

the material

Standard Aircraft Practices

• Repairs must use the same gauge of material, or one thicker.

• Substitution of alloy cannot alter this rule

• How long should a 3/32” rivet be to join two sheets of .040” using Standard

Aircraft Practices?

• How long should a 3/32” rivet be to join two sheets of .040” using Standard

Aircraft Practices?

• Answer: .040 + .040 + .098 + .049 = .230 (or about 7/32”)

Rivet Spacing

• Rivet Spacing. In no case should rivet spacing be closer than three diameters

center to center. The maximum spacing depends upon the strength needed and

possibility of the metal buckling between rivets. As a general rule, the maximum

rivet spacing should not be over 24 times the thickness of the thicker sheet. A

rivet pattern may be indicated on drawings as shown in the next slide.

Riveting

• Can use hand-setting methods (hammer and anvil, with various snaps)

• Or pneumatic riveting tools

– 3x riveting gun

– 4x riveting gun

• Or pneumatic squeezer tool

Riveting

• Must set a rivet as quickly as possible to avoid work hardening (as few blows

as possible)

• Don’t set the gun too low

Hammer Riveting

• check hammer face, if required, remove any damage

• check rivet snap, if required, remove any damage

• brace your material holding hand against the vice and/or snap stand

• don’t choke the hammer - let the weight of the hammer do the work

• get a comfortable height to the vice, stand on something if necessary

• put in some peripheral rivets to locate the sheets

Hammer Riveting

• install the rivets sequentially (except for a few to locate) so that the hammer

has room to get at the rivet

• close attention should be paid to each hammer blow and the result on the

rivet.

• feel the way the hammer hits; feel the rebound; a square hit will bounce

straight back

• make slight adjustments with each hit

• all riveted surfaces should be flat and free of distortion; the surface of the

sheet should look as if just the rivet heads have been set down on a mirror.

Rivet gun setting

• Rivet snap should dent the wood, but not shatter it.

Gooseneck-style rivet gun

• Good balance

• Exposed trigger

Kev’s AME Structures

Section IV – Bending and Forming

Bending and Forming

• Definition: Forming ~ changing the shape of a piece of metal by bending and

deforming the material

• Aluminum alloys are compatible with bending techniques providing certain

guidelines are maintained. One basic theory relates to the radius of the

bend. Given a piece of 2024T3 of .064” thickness, we can manufacture a straight

line bend if we use a guideline of 3 – 5 times the thickness. Consult one of the

many common charts indicating recommended bend radius’ for 90°, given

material thicknesses. (see page 2-70 in Airframe text, figure 2-127) The whole

point of using a minimum bend radius is the avoidance of cracks, and it must be

noted that sheet metal should be bend at an optimal angle of 90° to the grain.

Bending and Forming

• Forming includes:

– Bending

– Brake forming

– Stretch forming

– Roll forming

– Drawing

– Spinning

– Shear forming

– Flexible die forming

Bending and Forming

• The practice of bending a piece of sheet metal is to form the metal around a

radiussed corner similar to “cutting” a street corner with your bicycle. The metal

takes a short cut. On the inside of the bend, the metal surface shrinks and the

outside surface stretches. If there existed an invisible line through the inside of

the metal, equi-distant from both surfaces, this would be called the neutral plane

or neutral axis.

Neutral Axis

• We’ll use this invisible line for our calculations, because using either surface

would require calculations for the stretching or shrinking factors. If you need a

formula for calculating this imaginary location, use Thickness divided by

two. (T/2)

Bend Allowance

• Imagine the nose bar of the bending brake forming an entire circular shape,

instead of its’ existing unusual shape. Say the radius bar is using a ¼”

radius. (What is that diameter, then? Half Inch, you say?) Let’s use the formula

•

• BA = 2 pi (R + T/2)

• 360

Bends of 90°

• And if we know that we’re only accomplishing a simple 90° bend, then the

formula can be simplified to:

•

• BA = 2 pi (R + T/2 )

• 4

Amount of material in the bend

• This formula establishes Bend Allowance, which is the exact amount of

material that will be consumed in the bend, and only the bend. The workings of

this formula complete like this:

•

• BA = 2 x 3.1428 ( .250 + .064 / 2 )

• 4

Complete the calculations

• BA = 6.2856 ( .250 + .032 )

• 4

•

• BA = ( 1.5714 + .201 )

• 4

•

• BA = 1.7724

• 4

•

• BA = .443

Chart vs. Formula

• Any differences between this calculation and those bend allowances found on

a chart are related to the exact positioning of the neutral axis, and will only

produce a very tiny amount of error that is within the tolerances of forming and

bending sheet metal by hand.

Another piece of the puzzle

• You have now produced the exact amount of material that will be consumed

when the metal “cuts the corner” around the radius bar of the bending

brake. From this, we can begin further steps in the layout.

Setback

• Most aircraft sheet metal shops feature at least a cornice brake, or perhaps a

leaf brake (sometimes called a pan brake). The latter can be used for bending all

four edges of a pan-shaped structure. Setback is the distance from the bend

tangent line to the mold point.

Mold Point

• Think of the mold point as the exact location where the bend would be if it

were truly a 90° sharp-cornered bend. Another way of illustrating this point is to

extend the straight lines of your bend to a point where they join. That is the mold

point. Setback is used to calculate how much material is not used in the bend ~

kind of the opposite of the bend allowance.

Setback

• We have the standard formula for setback as:

• Setback = Radius + Thickness

(when we are bending 90 degrees.)

K-Factor, for other than 90°

• . For angles other than 90 degrees, we must use a K-factor in front of the

(Radius + Thickness) to compensate for the difference in angles. Here’s the K-

factor formula:

Setback = K ( R + T )

Use the open or closed angles

• It should be pointed out that if we perform bend OVER 90°, we must use the K-

factor for the entire bend that will be performed on the metal. A 45-degree closed

angle (What’s the definition of a closed angle? Past Ninety degrees) will require

a K-factor related to 135 degrees, not 45. For our purposes, there are K charts

that will provide the K-factor much simpler than computing it.

• To return to our bend of .064 metal, we’ll stay with the simple formula of

• Setback = Radius + Thickness

• Setback = .250 + .064

• Setback = .314

• Setback will be used as a deduction from our pattern layout of each flat

section, and is used twice for those sections affected by 2 bends.

Start the layout

• Let’s put the bend allowance and setback into a layout. A simple U-channel

incorporating two bends will be used, and continue with our thickness of .064

2024 T3, and 90° bends. Outside dimensions of the formed part should measure

2.00 inches after bending on all three sides.

Start the layout

• Start with a generous width of material with which to work. Layout each flat

section of 2 inches separated by a line which will represent the mold point.

• Subtract from each flat section the setback of .314”, and subtract an extra

setback from the center flat section which is affected by two bends. Each outside

flat section now measures 1.69, and the center flat section measures 1.37”. Each

dimension can now be marked with a non-leaded pencil, but never with a

scribe. (why?) We still have yet to add in the bend allowance, which occupies a

space between each flat section. Add in the BA (calculated to 0.44”) in two

places.

Continuing the layout

• You now have dimensions of two outside flat sections, a center flat sections,

and two bend allowances. Add all of these together to find the total amount of

material that will be required to manufacture this part. If done correctly, your

calculations should show 5.63 inches of material required to form a part with

three equal sides of 2 inches each.

Sight lines

• One final dimension should be discussed; that of a sight line. Sight lines are

used to properly position the metal in the bending brake such that the bends

begin and end exactly where we calculated. It is placed exactly one radius’ from

a bend tangent line, and it is important to know WHICH bend tangent to measure

from.

Sight lines

• Decide which end of your project will be clamped into the bending brake, and

which will hang out over the bending leaf. Draw the sight line from the btl which

will be clamped underneath the radius bar of the brake. The sight line gives an

exact position, when viewed from directly above, where the align your part.

Spring back

• When bending, don’t forget about Spring Back. This is related to the temper

of the material used, and should be compensated for during the bending

motion. Bend the material past the 90-degree point slightly, and check the spring

back for an exact right angle bend.

Relief Holes

• A quick mention should be made about relief holes: these are necessary to

relieve stresses that would occur if making two (or more) intersecting

bends. Relief holes are commonly found at the extreme corners of a pan shape.

Relief Holes

• Relief holes should be larger than the bend radius, and it is important to

deburr them completely. Ensure relief holes are at the intersection of the inside

bend tangent lines. Also, material on the sides of the pan shape may be cut back

slightly to allow for non-interference with each other after bending.

Bending and Forming

• Cornice Brake is the most common in aviation shops

• Also known as the standard hand brake

Cornice brake (standard hand brake)

Bending and Forming

• Other types include the box (or pan) brake which use smaller nose bars

• And the Bar former, or bench former

• Samples of these downstairs in our hangar

Bending and Forming

• Spring Back: the tendency of a material to return to its’ original shape

• Most often spring back is seen after a bending operation on a stiff metal

• Consider spring back whenever bending a sheet of metal. 7 – 10% is not

unusual.

Bending and Forming

• Various nose bars are used to change the radius of the bend

• MBR : “Minimum Bend Radius”

• MBR is generally:

– 1X thickness for O temper material

– 2.5X thickness for T4 temper material

– 3X thickness for T3 temper material

Bending and Forming

• Bend Allowance is that amount of material that is consumed in the bend. The

Bend Allowance begins and ends at the Bend Tangent Lines

• BTL (Bend Tangent Lines) are the lines which define the beginning and

ending of the curved portion

Bending and Forming

• Bend allowance chart is on page 2 – 72 of the airframe text

• Or a good formula is:

– B/A = 2 pi(R + T) x N/360

– Where R is the radius, T is thickness

– And N is the number of degrees in the bend

• Or you can use the empirical formula:

– B/A = 0.01743 x R + 0.0078 x N

Bending and Forming

• Setback: the amount of material that is deducted from a Bend Allowance

Open & Closed Angles

• An open angle is measured as any angle which has not passed the 90°

Open & Closed Angles

• A closed angle is defined as an angle where the metal has been bent PAST the

90° point

Kev’s AME Structures

Part V

Special Fasteners

Special Fasteners

• When it is impossible to get inside a structure to buck a solid rivet, in certain

cases it may be permissible to use blind rivets

• Most common style is the self-plugging mechanical-lock rivet

Special Fasteners

• Certain types of self-plugging blind rivets may be used to replace solids size for

size, but generally they are required to increase one diameter

• The reason is a fail-safe; if the stem fails to become an integral part of the rivet,

the hollow shank will have less strength

Applicability

• Blind rivets will not be used in the following areas:

– Jet intake areas

– Floats or hulls, below the water line

– Wing attachment fittings

– Control surface hinge brackets

– Landing gear fittings

– Tanks containing fluids

Special Fasteners

• Early knob-stem blind rivets

• Not discontinued, but in very limited use

• Used friction to prevent stem removal

Special Fasteners

• Note that blind rivets should not be used on floats or amphibian hulls below the

water line

• If it is possible to install a solid rivet, that is the preferred fastener

• Most blind rivets require special pulling tools to install.

Special Fasteners

• Serrated stem blind rivets

• Includes mechanical locking rings around the centre stem.

• Includes Cherry Max, Cherry Lock, Olympic Lok, Huck Lok.

Friction Lock Rivets

• Blind head is formed by pulling the tapered stem into the hollow shank

• Shank swells, and clamps skins together

• Stem breaks off at a predetermined tension, but requires shaving to complete

the smooth appearance

Friction Lock Rivets

• Friction lock rivets are susceptible to vibration and smoking

• Stems fall out and weaken the installation

• Not recommended for structural applications

Friction Lock Rivets

• Removal is simple:

• Punch the stem through

• Drill out the shank similar to solid rivet removal procedures

Mechanical Lock Rivets

• Mechanical lock rivets may replace solid rivets on a size-for-size basis.

• This type of rivet features a positive locking ring on the center stem to prevent

removal

• Locking ring is carried on each rivet around the main stem, above the rivet

head prior to pulling the rivet.

Mechanical Lock Rivets

• Installation procedures:

– Drill the appropriate size hole

– Estimate the grip length using the hook grip gauge tool

– Install the appropriate grip length rivet

– Place the pulling tool over the stem of the blind rivet (mechanical or

pneumatic)

Mechanical Lock Rivets

• Installation procedures, continued:

– Stem is pulled into the rivet puller, through the center of the shank, bulging the

shank near the skin

– Bulging action clamps skins together as stem continues to pull through the

center

– Bulb becomes fully formed; hole-filling is completed

Mechanical Lock Rivets

• Installation procedures, continued:

– Stem shears off at the narrowest point, at a predetermined tension

– Stem locking collar is forced into place at the same time, gripping the

remainder of the stem inside the rivet head

– Stem comes completely free

– If properly done, no shaving will be required ~ stem will break free at the rivet

head surface.

Mechanical Lock Rivets

• Come in both universal and countersunk head styles

• Very sensitive to hole diameter and grip length

• Older Cherry-Lock rivets had a bad tendency to lose their locking rings, or

leave them protruding.

Mechanical Lock Rivets

• Cherry Max rivets available in diameters of 1/8”, 5/32”, 3/16”, and 1/4”

• Lengths increment in 1/16” – use the grip gauge

• They feature oversized diameters for each size.

• Cherry Max rivets use a washer around the stem above the rivet head to set

the locking ring, as opposed to Cherry Lock which does not have the washer.

Mechanical Lock Rivets

• Olympic Lok rivets are a three piece rivet

• Do not shave or file the head of an olympic lok; it weakens the locking ring

attachment points

• Only available in three sizes: 1/8, 5/32 and 3/16

Mechanical Lock Rivets

• Huck lok rivets come in same sizes as Cherry Max

• Has good abilities to clamp-up skins

• Requires greater skill to remove

Commercial Pop rivets

• Do not use commercial pull-type pop rivets to effect aircraft repairs

• In some cases, certain pop-rivet pullers may be used to pull Cherry Max

rivets. They will not function on Cherry Lock fasteners.

Common blind rivet installation defects

• Oversize or elongated hole

• Incorrect grip length

• Burrs

• Gap between sheets

• Angled rivet head, or angled tooling

Go – NoGo gauges

• Certain companies manufacture special tools to estimate hole sizes for blind

rivets

• If the “Go” side of the gauge fits, the rivet will fit.

• If the “No-Go” side fits, the hole is too large for that size of rivet

Grip lengths

• Unacceptable grip length; no shank protrusion

• Acceptable grip length; small amount of shank protruding (but not too much)

Head Markings

• If numbers are present on blind rivet heads, they represent grip lengths

Comparisons: Cherry Max to Cherry Lock

• Much less tooling for Cherry Max; one pneumatic tool or a single hand puller

will install all sizes

• More reliable rivet installation; less lock ring fallout on Cherry Max rivets

• Cherry Max available in 5056 aluminum or Monel

Comparisons: Cherry Max to Cherry Lock

• Cherry Lock pneumatic tools are larger, heavier, and much more

complicated. Prone to problems. Mechanical pulling heads are complicated, and

require elaborate procedures to change.

• Cherry Lock rivets are more prone to “pulling” problems; stems break early,

or not at all, and lock rings fail to seat

Cherry Max removals

• Remove lock ring by one of the following methods:

– Drill-off

– Cutting wheel

– Sanding disk

• Drive center stem through with a small pin punch

• Remove rivet head with similar procedures to solid rivets

Cherry Max part numbers

• CR 3213 – 4 – 6 (sample part number)

• Breaks down into:

– CR3 Cherry Rivet

– 2 Barrel Material

– 1 Rivet type: Nominal (4 is oversize)

– 3 Universal head (Countersunk = 2)

– - 4 Shank, in 1/32’s

– - 6 grip length in 1/16’s

Notes

• Cherry Max driving anvil on countersunk rivets is Gold to indicate nominal

diameters

• Grip gauge shown here:

HiLoks

• The hi-lok fastener combines the features of a rivet and a bolt and is used for

high-strength, interference-free fit of primary structures. The hi-lok fastener

consists of a threaded pin and threaded locking collar.

Hi-Lok Fasteners

• The pins are made of cadmium-plated alloy steel with protruding or 100-

degree flush heads. Collars for the pins are made of anodized 2024-T6 aluminum

or stainless steel.

Hi-Lok Fasteners

• The threaded end of the pin is recessed with a hexagon socket to allow

installation from one side. The major diameter of the threaded part of the pin has

been truncated (cut undersize) to accommodate a 0.004-inch maximum

interference-free fit.

Hi-Lok Fasteners

• One end of the collar is internally recessed with a 1/16-inch, built-in variation

that automatically provides for variable material thickness without the use of

washers and without fastener preload changes. The other end of the collar has a

torque-off wrenching device that controls a predetermined residual tension of

preload (10%) in the fastener.

Hi Shear fasteners

• Manufactured by the Hi Shear corporation

• Used in high shear strength applications

• Quick to install; lighter than bolts/nuts

• Pins usually made of steel, but some aluminium pins available

• Requires “necked” pin and a swedged collar

• Used in thick material areas

Hi Shear fasteners

• Collar is driven onto the necked portion of the pin with a rivet gun; part of the

collar shears off, and the remaining is compressed into a tight ring around the pin

neck.

• Possible to use pneumatic squeezers and special adapters

• See page 125 and onwards for further info.

Jo-Bolt Fasteners

• The jo-bolt is a high-strength, blind structural fastener that is used on difficult

riveting jobs when access to one side of the work is impossible. The jo-bolt

consists of three factory-assembled parts: an aluminum alloy or alloy steel nut, a

threaded alloy steel bolt, and a corrosion-resistant steel sleeve. The head styles

available for jo-bolts are the 100-degree flush head, the hexagon protruding head,

and the 100-degree flush millable head.