Riveted Joints in Aircraft Manufacture

Riveted Joints

• Three types of riveted joints are used in aircraft manufacturing and repair: lap joints, flush joints, and joggle joints.

Lap Joints

• In a lap joint, the skins are riveted together, resulting in a distinct step or change in levels.
• The skins are not on the same plane, but are stacked.
• Lap joints are not suitable for aerodynamic smoothness due to disrupted airflow during flight.
• They are generally used on light aircraft where aerodynamic smoothness is not a concern.
• Lap patches are an example of where lap joints are used.

Flush Joints

• Flush joints are used to obtain aerodynamic cleanliness between two skins.
• The skins are riveted to the same substructure, putting them on the same plane.
• The substructure can be longerons, bulkheads, formers, etc.
• A separate metal piece called a doubler may also be used as the substructure.
• Flush patches are an example of a flush joint.

Joggle Joints

• A joggle joint is a combination of flush and lap joints.
• One skin is joggled to accommodate the other, producing one smooth side.
• Joggle joints are also used when fitting doublers over other internal structure.

Deburring

• Holes should be deburred after drilling using special deburring tools.
• If a deburring tool cannot be sourced, use a larger diameter drill bit to achieve similar results.

Solid Riveting Tools

• Solid rivets can be closed by hand using appropriate snaps, sets, and dollies.
• A set (also known as a draw tool) is a hollow punch used to draw the metal sheets together and bring the preformed rivet head against the metal surface.
• A snap is a form of punch with a recess at one end, the same shape as the rivet preformed head.
• A dolly is a metal block with a recess the same shape as the preformed head of the rivet, used to support the preformed rivet head.

Hand Riveting

• Hand riveting may be convenient for small jobs or those done away from the aircraft.
• When solid rivets are closed with a hand hammer, the preformed head should be supported in a dolly.
• A hollow set or draw tool is used to ensure the sheets are drawn together.
• The tail is then driven using a flat snap to form a reaction head with a thickness of 0.5D.

Pneumatic Rivet Guns

• Aircraft solid rivets are often driven with pneumatic rivet hammers or guns.
• Pneumatic rivet guns use compressed air to drive a piston back and forth, applying a hammering action to the rivet snap.
• This method offers several advantages, including producing uniformly sized shop heads, reducing installation time, and being suitable for use with two types of guns: C-yoke and alligator yoke.

Bucking Bars (Dollies)

• The shop head is formed by the bucking or vibrating action of a bucking bar when the rivet gun is activated.
• Bucking bars come in many different sizes and shapes for different applications.
• The driving face of the bar is machined smooth and polished so that no marks are left on the rivet tail.

Using the Rivet Gun

• Prior to installing rivets, the gun needs to be adjusted for correct pressure/hammer.
• This is achieved by actioning the gun against a piece of wood and adjusting the airflow to indent the wood but not shatter it.
• Place a rivet in the hole and hold the gun against its head with enough pressure to keep the rivet against the skin.
• Hold the bucking bar flat and square against the rivet’s tail and pull the trigger to form the rivet.

Common Riveting Errors

• Burr under head: not deburred correctly.
• Cut shop head: dolly did not cover entire end of rivet.
• Cracked shop head: hard rivet or hit too long.
• Skin marked by oversize rivet set: set head is too big for rivet.
• Skin marked by rivet set: set not centered on head of rivet.

NACA Riveting

• NACA (National Advisory Committee for Aeronautics) flush riveting technique is used to install a rivet with a flush shop head.
• The skin is countersunk and the rivet installed from inside the structure.
• The rivet is driven to fill the countersink.
• A micro-shaver is then used to mill the excess material from the shank and obtain a flush surface.