Removal of Rivets
When a rivet has to be replaced, remove it carefully to retain the rivet hole’s original size and shape. If removed correctly, the rivet does not need to be replaced with one of the next larger size. Also, if the rivet is not removed properly, the strength of the joint may be weakened and the replacement of rivets made more difficult.
When removing a rivet, work on the manufactured head. It is more symmetrical about the shank than the shop head, and there is less chance of damaging the rivet hole or the material around it. To remove rivets, use hand tools, a power drill, or a combination of both.
The procedure for universal or protruding head rivet removal is as follows:
- File a flat area on the head of the rivet and center punch the flat surface for drilling. NOTE: On thin metal, back up the rivet on the upset head when center punching to avoid depressing the metal.
- Use a drill bit one size smaller than the rivet shank to drill out the rivet head. NOTE: When using a power drill, set the drill on the rivet and rotate the chuck several revolutions by hand before turning on the power. This procedure helps the drill cut a good starting spot and eliminates the chance of the drill slipping off and tracking across the metal.
- Drill the rivet to the depth of its head, while holding the drill at a 90° angle. Do not drill too deeply, as the rivet shank will then turn with the drill and tear the surrounding metal. NOTE: The rivet head often breaks away and climbs the drill, which is a signal to withdraw the drill.
- If the rivet head does not come loose of its own accord, insert a drift punch into the hole and twist slightly to either side until the head comes off.
- Drive the remaining rivet shank out with a drift punch slightly smaller than the shank diameter.
On thin metal or unsupported structures, support the sheet with a bucking bar while driving out the shank. If the shank is unusually tight after the rivet head is removed, drill the rivet about two-thirds through the thickness of the material and then drive the rest of it out with a drift punch. Figure 4-98 shows the preferred procedure for removing universal rivets.
The procedure for the removal of countersunk rivets is the same as described above except no filing is necessary. Be careful to avoid elongation of the dimpled or the countersunk holes. The rivet head should be drilled to approximately onehalf the thickness of the top sheet. The dimple in 2117–T rivets usually eliminates the necessity of filing and center punching the rivet head.
To remove a countersunk or flush head rivet, you must:
- Select a drill about 0.003-inch smaller than the rivet shank diameter.
- Drill into the exact center of the rivet head to the approximate depth of the head.
- Remove the head by breaking it off. Use a punch as a lever.
- Punch out the shank. Use a suitable backup, preferably wood (or equivalent), or a dedicated backup block. If the shank does not come out easily, use a small drill and drill through the shank. Be careful not to elongate the hole.
Replace rivets with those of the same size and strength whenever possible. If the rivet hole becomes enlarged, deformed, or otherwise damaged, drill or ream the hole for the next larger size rivet. Do not replace a rivet with a type having lower strength properties, unless the lower strength is adequately compensated by an increase in size or a greater number of rivets. It is acceptable to replace 2017 rivets of 3⁄16-inch diameter or less, and 2024 rivets of 5⁄32-inch diameter or less with 2117 rivets for general repairs, provided the replacement rivets are 1⁄32-inch greater in diameter than the rivets they replace.
National Advisory Committee for Aeronautics (NACA) Method of Double Flush Riveting
A rivet installation technique known as the National Advisory Committee for Aeronautics (NACA) method has primary applications in fuel tank areas. [Figure 4-99] To make a NACA rivet installation, the shank is upset into a 82° countersink. In driving, the gun may be used on either the head or shank side. The upsetting is started with light blows, then the force increased and the gun or bar moved on the shank end so as to form a head inside the countersink well. If desired, the upset head may be shaved flush after driving. The optimal strength is achieved by cutting the countersink well to the dimensions given in Figure 4-100. Material thickness minimums must be carefully adhered to.