Rivet Installation Tools.........................................4-36 Riveting Procedure ...............................................4-40 Countersunk Rivets...............................................4-41 Evaluating the Rivet .............................................4-44 Removal of Rivets ................................................4-45 Replacing Rivets...................................................4-46 National Advisory Committee for Aeronautics....4-46 (NACA) Method of Double Flush Riveting .........4-46 Special Purpose Fasteners ........................................4-47 Blind Rivets ..........................................................4-47 Pin Fastening Systems (High-Shear Fasteners) ...4-50 Lockbolt Fastening Systems .................................4-52 Blind Bolts ............................................................4-53 Rivet Nut...............................................................4-56 Blind Fasteners (Nonstructural)............................4-56 Forming Process...........................................................4-57 Forming Operations and Terms ...................................4-57 Stretching .................................................................4-58 Shrinking ..................................................................4-58 Bumping ...................................................................4-58 Crimping...................................................................4-58 Folding Sheet Metal .................................................4-58 Layout and Forming.....................................................4-59 Terminology .............................................................4-59 Layout or Flat Pattern Development ........................4-60 Making Straight Line Bends.....................................4-60 Bending a U-Channel ...........................................4-61 Using a J-Chart To Calculate Total Developed  Width ....................................................................4-67 How To Find the Total Developed Width  Using a J-Chart .....................................................4-68 Using a Sheet Metal Brake to Fold Metal ................4-69 Step 1: Adjustment of Bend Radius......................4-69 Step 2: Adjusting Clamping Pressure ...................4-70 Step 3: Adjusting the Nose Gap............................4-71 Folding a Box ...........................................................4-72 Relief Hole Location.............................................4-73 Layout Method......................................................4-73 Open and Closed Bends ...........................................4-73 Open End Bend (Less Than 90°) ..........................4-74 Closed End Bend (More Than 90°) ......................4-74 Hand Forming ..........................................................4-74 Straight Line Bends ..............................................4-74 Formed or Extruded Angles..................................4-75 Flanged Angles .....................................................4-76 Shrinking...............................................................4-76 Stretching..............................................................4-77 Curved Flanged Parts............................................4-77 Forming by Bumping............................................4-79 Joggling.................................................................4-81 Lightning Holes ....................................................4-82 Working Stainless Steel............................................4-83 Working Inconel$^{®}$ Alloys 625 and 718 ....................4-83 Working Magnesium................................................4-84 Working Titanium ....................................................4-85 Description of Titanium........................................4-85 Basic Principles of Sheet Metal Repair .......................4-86 Maintaining Original Strength..................................4-87 Shear Strength and Bearing Strength .......................4-88 Maintaining Original Contour ..................................4-89 Keeping Weight to a Minimum................................4-89 Flutter and Vibration Precautions.............................4-89 Inspection of Damage...............................................4-90 Types of Damage and Defects..................................4-90 Classification of Damage .........................................4-91 Negligible Damage ...............................................4-91 Damage Repairable by Patching...........................4-91 Damage Repairable by Insertion ..........................4-92 Damage Necessitating Replacement of Parts .......4-92 Repairability of Sheet Metal Structure ........................4-92 Structural Support During Repair.............................4-92 Assessment of Damage ............................................4-92 Inspection of Riveted Joints .....................................4-92 Inspection for Corrosion...........................................4-93 Damage Removal .....................................................4-93 Repair Material Selection .....................................4-93 Repair Parts Layout ..............................................4-93 Rivet Selection......................................................4-94 Rivet Spacing and Edge Distance.........................4-94 Corrosion Treatment.............................................4-94 Approval of Repair...................................................4-94 Repair of Stressed Skin Structure.............................4-94 Patches ..................................................................4-97 Typical Repairs for Aircraft Structures ....................4-98 Floats.....................................................................4-99 Corrugated Skin Repair ........................................4-99 Replacement of a Panel ........................................4-99 Outside the Member .............................................4-99 Inside the Member ................................................4-99 Edges of the Panel ................................................4-99 Repair of Lightning Holes ....................................4-99 Repairs to a Pressurized Area .............................4-101 Stringer Repair....................................................4-102 Former or Bulkhead Repair ................................4-103 Longeron Repair .................................................4-104 Spar Repair .........................................................4-104 Rib and Web Repair............................................4-105 Leading Edge Repair ..........................................4-106 XIX