Sheet Metal 3: special fasteners

Non-Solid Rivet Fasteners

• Non-solid rivets are fasteners used in applications where one side of the work is inaccessible.
• Blind rivets are hollow and weaker than solid rivets.
• To retain joint strength, stronger materials, larger diameter rivets, or more rivets can be used.
• Blind rivets are 20–50% heavier than solid rivets due to their steel stem.
• The exterior of a riveted patch fuselage skin uses solid fasteners, except in the middle of the patch in some applications.
• On the interior of a riveted fuselage skin patch, the stringer may prevent bucking a solid rivet.
• Blind rivets are the only option when access is restricted.

Friction Lock Rivets

• Friction-lock rivets are a type of blind rivet.
• Originally available in two styles: hollow shank pull-through and self-plugging types.
• The pull-through type is less common.
• The self-plugging Cherry friction-lock rivet is still used for repairing light aircraft.
• Friction-lock rivets cannot replace solid shank rivets of the same size.
• Must be at least one size larger in diameter if used to replace a solid shank rivet.
• If the center stem of a friction-lock rivet falls out due to vibrations or damage, it loses considerable strength.
• The Cherry friction-lock rivet was one of the early forms of blind rivets widely used for aircraft construction and repair.
• Cherry friction-lock rivets come in two head styles: universal and 100-degree countersunk.
• They are typically supplied in three standard diameters: 1/8, 5/32, and 3/16 inch.

Mechanical-Lock Blind Rivets

• Mechanical locking blind rivets were developed after friction lock rivets.
• These rivets have a built-in mechanical lock to retain the rivet stem in the shank.
• As they have many components and intricate mechanics, they are typically more expensive than solid rivets.
• Mechanical-lock rivets need special installation tools and gauges to be installed properly.
• Installation instructions should be carefully followed.

Huck-Lok Rivets

• Huck-Lok rivets were among the first mechanical lock rivets used to replace solid rivets.
• Their use is limited to manufacturers and large repair facilities due to the high cost of installation tooling.

CherryMAX Rivets

• CherryMAX rivets have less expensive installation tools

• Improved rivet head flushness

• One of the most commonly used mechanical lock blind rivets in general aviation.

• Properly installed CherryMAX rivets often exhibit a higher shear strength than similarly sized solid rivets.

• Hole size and grip length are crucial for correct CherryMAX rivet installation.

• Four standard diameters are available: 1/8, 5/32, 3/16, and ¼ inch.

• Oversize versions are available in 1/64" increments of standard diameters.

• Grip lengths are available in 1/16" increments.

Mechanical Lock Cherry Rivets

• Has a complex multiple step installation cycle for each fastener
• Special tooling heads are required for each size and head shape
• Can be used to replace solid rivets
• Various sleeve material available
• Correct length is critical

Olympic-Lok Rivets

• Require a specific installation tool.
• Designed to be lightweight.
• Available in 8 different alloys.
• Marketed as a low-cost option.

High Shear Rivets

• Introduced in the 1940s.
• Used in applications involving high shear loads.
• Provide the same strength as an AN bolt.
• Feature an interference fit, reamed to a specific tolerance.
• Constructed with a pin and collar assembly.
• Collar is swaged on during installation.
• The shank's size does not decrease.

Lockbolts

• Lockbolts are manufactured to handle shear and tension stress.
• They are mostly used in high-strength areas of jet aircraft.
• Used for landing gear, engine to wing spar, and wing to fuselage attachments.
• Lockbolts come in diameters ranging from 1/8" to 3/8".
• Both nominal and oversize options are available.
• Can be made from aluminum, steel, and CRES (corrosion-resistant steel) materials.
• Heads are available in countersunk or protruding styles.
• Lockbolts can be installed in three different ways: pull, stump, and blind.
• Because of tooling costs, they are generally not used in general aviation.

Hi-Lok Fasteners

• Used in structural locations on all aircraft.
• Interference fit
• HI-Loks can be installed with special or standard hand tools.
• Feature a straight shank with threads on the end.
• Locking collar threads are used.
• The collar shears off when the specified torque is reached.
• The shank doesn't stretch.
• Available in different alloys: aluminum, steel, stainless steel, and titanium.

High-Light Fasteners

• Offer a better strength-to-weight ratio than Hi-Lok fasteners.
• The transition between the shank and the thread is shorter.
• Uses the same locking collar as the Hi-Lok fastener.

Hi-Lok Hi-Tigue Fasteners

• Has non-straight shank
• Has a bead that preloads the hole, resulting in increased joint strength
• Preloaded condition prevents cyclic action that causes cold working
• Can carry both tension and shearing loads at the same time

Taper-Lok Fasteners

• These are not straight shank fasteners.
• The design preloads the hole.
• Considered the strongest of the special fasteners.

CherryBUCK Fasteners

• This fastener is a bi-metallic, one-piece unit.
• Combines a shank with a shear strength of 95 ksi with a ductile titanium-columbium tail.
• Interference fit design
• Driven like a normal solid rivet
• Shank doesn't expand
• One-piece design means there is zero risk of Foreign Object Damage (FOD).
• Has a 600° F allowable temperature.
• Very low backside profile

Jo-Bolt Fasteners

• High-strength structural fastener.
• It is used in close tolerance holes.

Rivnut Fasteners

• Rivnuts feature both a countersunk head and a flat head design.

Anchor Nuts

• AN336F: Two-Lug Anchor Nut
• NAS1025: One-Lug Anchor Nut
• NAS1027: Corner Anchor Nut
• AN256F: Right-Angle Anchor Nut
• AN362F: High-Temp, Two-Lug Anchor Nut
• Two-Lug Floating Anchor Nut
• Ganged Anchor Nuts are also available

Instrument Anchor Nut

• Specialty type of anchor nut used for instruments

Tinnerman Fasteners

• Fasteners with stamped self-threading nuts.

Dzus Fasteners

• Require a quarter turn to lock/unlock.
• The slot should be aligned with the airstream or panel edge to allow quick inspection.
• They are used on access panels that are opened frequently
• Take care that fasteners does not go to side of spring
• Do not over tighten
• May have wing nut head
• A Dzus key or a specially grounded screwdriver is required to lock or unlock it.

Airlock Fasteners

• Fastener consists of three parts: a stud, a cross pin, and a stud receptacle.
• The studs are manufactured from steel and case hardened.
• Case hardening is done to prevent excessive wear.
• The stud hole is reamed for a press fit of the cross pin.

Cam Lock Fasteners

• Spring loaded
• 90 degree turn and lock
• Held in place with a washer