rivet in a joint will indicate that it has been too highly loaded, with the possibility that neighboring rivets may have partially failed.
Shear Failure Shear failure is perhaps the most common of rivet failures. It is simply a breakdown of the rivet shank by forces acting along the plane of two adjacent sheets, causing a slipping action which may be severe enough to cut the rivet shank in two. If the shank becomes loaded beyond the yield point of the material and remains overloaded, a permanent shift is established in the sheets and the rivet shank may become joggled.
Bearing Failure If the rivet is excessively strong in shear, bearing failure occurs in the sheet at the edge of the rivet hole. The application of large rivets in thin sheets brings about such a failure. In that case, the sheet is locally crushed or buckled, and the buckling destroys the rigidity of the joint. Vibrations, set up by engine operation or by air currents in flight, may cause the buckled portion to flutter and the material to break off close to the rivet head. If buckling occurs at the end of the sheet, a tear-out may result. In either case, replacement of the sheet is necessary.
Head Failure Head failure may result from complex loadings occuring at a joint, causing stresses of tension to be applied to the rivet head. The head may fail by shearing through the area corresponding to the rivet shank, or, in thicker sheets, it may fail through a prying action which causes failure of the head itself. Any visible head distortion is cause for replacement. This latter type of head failure is especially common in blind rivets.
Rivet Inspection To obtain high structural efficiency in the manufacture and repair of aircraft, an inspection must be made of all rivets before the part is put in service.
This inspection consists of examining both the shop and manufactured heads and the surrounding skin and structural parts for deformities. A scale or rivet gage can be used to check the condition of the upset rivet head to see that it conforms to the proper requirements. Deformities in the manufactured head can be detected by the trained eye alone. However, on flush rivets, a straightedge can be used as shown in figure 5-53.
Rivet gage Straightedge.
FIGURE 5-53. Tools used to gage rivets.
Some common causes of unsatisfactory riveting are improper bucking, rivet set slipping off or being held at the wrong angle, and rivet holes or rivets of the wrong size. Additional causes for unsatisfactory riveting are countersunk rivets not flush with the well; work not properly fastened together during riveting; the presence of burrs, rivets too hard, too much or too little driving; and rivets out of line.
Occasionally, during an aircraft structural repair, it is wise to examine adjacent parts to determine the true condition of neighboring rivets. In doing so, it may be necessary to remove the paint. The presence of chipped or cracked paint around the heads may indicate shifted or loose rivets. Look for tipped or loose rivet heads. If the heads are tipped or if rivets are loose, they will show up in groups of several consecutive rivets and will probably be tipped in the same direction. If heads which appear to be tipped are not in groups and are not tipped in the same direction, tipping may have occurred during some previous installation.
Inspect rivets known to have been critically loaded, but which show no visible distortion, by drilling off the head and carefully punching out the shank. If, upon examination, the shank appears joggled and the holes in the sheet misaligned, the rivet has failed in shear. In that case, try to determine what is causing the shearing stress and take the necessary corrective action. Flush rivets that show head slippage within the countersink or dimple, indicating either sheet bearing failure or rivet shear 176
failure, must be removed for inspection and replacement.
Joggles in removed rivet shanks indicate partial shear failure. Replace these rivets with the next larger size. Also, it the rivet holes show elongation, replace the rivets with the next larger size. Sheet failures (such as tear-outs, cracks between rivets, and the like) usually indicate damaged rivets, and the complete repair of the joint may require replacement of the rivets with the next larger size.
The general practice of replacing a rivet with the next larger size (1/32 in. greater diameter) is necessary to obtain the proper joint strength of rivet and sheet when the original rivet hole is enlarged.
If the rivet in an elongated hole is replaced by a rivet of the same size, its ability to carry its share of the shear load is impaired and joint weakness results.
REMOVING RIVETS When removing a rivet for replacement, be very careful so that the rivet hole will retain its original size and shape and replacement with a larger size rivet will not be necessary. 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 will be 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 preferred method is to drill through the rivet head and drive out the remainder of the rivet with a drift punch. First, file a flat area on the head of any round or brazier head rivet, and center punch the flat surface for drilling.
On thin metal, back up the rivet on the upset head when center punching to avoid depressing the metal. The dimple in 2117-1 rivets usually eliminates the necessity of filing and center punching the rivet head.
Select a drill one size smaller than the rivet shank and drill out the rivet head. 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. Be careful not to drill too deep because the rivet shank will turn with the drill and cause a tear. The rivet head will often break away and climo the drill, which is a good 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 out the shank of the rivet with a drift punch slightly smaller than the diameter of the shank. On thin metal or unsupported structures, support the sheet with a bucking bar while driving out the shank. If the shank is exceptionally tight after the rivet head is removed, drill the rivet about two-thirds of the way through the thickness of the material and then drive out the remainder of the rivet with a drift punch.
The procedure for the removal of flush rivets is the same as that just described except that no filing is necessary. Be very careful to avoid elongation of the dimpled or the countersunk holes. The rivet head should be drilled to approximately one half the thickness of the top sheet.
SPECIAL RIVETS There are many places on an aircraft where access to both sides of a riveted structure or structural part is impossible, or where limited space wil not permit the use of a bucking bar. Too, in the attachment of many nonstructural parts, such as aircraft interior furnishings, flooring, deicing boots, and the like, the full strength of solid shank rivets is not necessary.
For use in such places, special rivets have been designed which can be bucked from the front. They are sometimes lighter than solid shank rivets, yet amply strong for their intended use. These rivets are manufactured by several corporations and have unique characteristics that require special installation tools, special installation procedures, and special removal procedures. Because these rivets are often inserted in locations where one head (usually the shop head) cannot be seen, they are also called blind rivets.
The various types of mechanically expanded rivets, their fabrication, composition, uses, selection, and identification were discussed in Chapter 6, Hardware, Materials, and Processes, in the Airframe and Powerplant. Mechanics General Handbook, AC 65-9A. The installation techniques will be covered in this section.
Installation Tools The tools used to install self-plugging (friction lock) rivets depend upon the manufacturer of the rivet being installed. Each company has designed special tools which should always be used to ensure satistactory results with its product. Hand tools as well as pneumatic tools are available.
After selection or determination of the rivet to be used in any installation, the proper size twist drill must be determined. Generally, manufacturers recommend the following finish drill sizes for the common shank diameters (figure 5-54).
Be very careful when drilling the material. Hold the drill at right angles to the work at all times to keep from drilling an elongated hole. The blind rivet will not expand as much as a solid shank rivet. If the hole is too large or elongated, the shank will not properly fill the drilled hole. Com mon hand or pneumatic powered drills can be used to drill the holes. Some manufacturers recommend predrilling the holes; others do not.
Equipment used to pull the stem of the rivet, as previously stated, will depend upon the manufacturer of the rivet. Both manually operated and power-operated guns are manufactured for this purpose. Nomenclature for various tools and assemblies available depends upon the manufacturer.
Application and use of the equipment is basically the same. Whether the equipment is called hand tool, air tool, hand gun, or pneumatic gun (figure 5-55), all of these are used with but one goal, the proper installation of a rivet.
The choice of installation tools is influenced by several factors: The quantity of rivets to be installed, the availability of an air supply, the accessibility of the work, and the size and type of rivet to be installed. In addition to a hand or power riveter, it is necessary to select the correct "pulling head" to complete the installation tool.
Selection of the proper pulling head is of primary importance since it compensates for the variables of head style and diameter. Since your selection will depend on the rivets to be installed, you should consult the applicable manufacturer's literature.
• SELF-PLUGGING (FRICTION LOCK) RIVETS Self-plugging (friction lock) rivets are fabricated in two common head styles: (1) A protruding head similar to the AN470 or universal head, and (2) a 100° countersunk head. Other head styles are available from some manufacturers.
The stem of the self-plugging (friction lock) rivet may have a knot or knob on the upper portion, or it may have a serrated portion as shown in figure
5-56.
The sequence of steps to follow in the installation of self-plugging (friction lock) rivets is basically the same as that for solid shank rivets, but the methods and equipment vary. The following steps are typical of any installation:
(1) Select the rivet to be installed-determined by thickness of material to be riveted, strength desired in assembly, and los cation of installation (protruding or coun tersunk head).
(2) Drill the hole (s) -determine sizé of twist drill to be used, do not elongate rivet hole, remove burrs, and use a stop countersink if necessary.
CHERRYLOCK COUNTERSINKING DIMENSIONS -c.→ - 010R.
UTI Mir.
3/32 #40 #30 .129 -097 .100 .132 100° A6520426 HEAD 100° NAS1097 HRAD 90°U #20 „160 .164 Max.
# 10 .192 _196 F .256 261 .182 .176 BULBED CHERRYLOCK .228 .222 .195 .189 .173 -167 S1/8 #27 .143 -146 ·289 .283 .246 .240 .216 ·210 5/32 #16 .176 .180 .356 .350 .302 .296 .258 .252 3/16 #5 .205 .209 479 473 ·395 ,389 FIcURE 5-54. Cherry rivet installation data 178
CHERRY RIVET GUN HUCK RIVET GUN 120
HAND TOOL G36
HAND TOOL G700
HYROSHIF T TOOL 139-A
AIR TOOL 0784
HYDROSHIF T TOOL 352
AIR TOOL FIGURE 5-55. Self-plugging (friction lock) rivet guns.
Satisfactory Unsatisfactory Grip length too short for material thickness Undersize Oversize hole hole FICURE 5-57. Inspection of self-plugging (friction lock) riveta.
Protruding Countersunk head head FICURE 5-56. Self-plugging (friction lock) rivets.
(3) Install the rivet-make certain the rivet head is seated firmly, position the selected *uch tool on the rivet stem, pull rivet stem until the stem snaps, apply approximately 15 Ibs. of pressure to the end of the stem, and trim the stem flush with the rivet head. If aerodynamic smoothness is a factor, the stem can be shaved with a rivet shaver. Drill head only Inspection The inspection of installed self-plugging (friction lock) rivets is very limited. Often the only inspec tion that can be made is on the head of the rivet. It should fit tightly against the metal. The stem of the rivet should be trimmed flush with the head of the rivet whether it is a protruding head or a countersunk head.
If you can see the shop head side of the installed rivet, inspect it for the requirements illustrated in figure 5-57. When the rivet head is considered unsatisfactory, remove the rivet and install another in FICURE 5-58. Removal of self-plugging (friction lock) ita place. rivets.
Removal Procedures Self-plugging (friction lock) rivets are removed in the same manner as solid shank rivets except for the preliminary step of driving out the stem (figure 5-58). The following steps should be used in their proper sequence:
(1) Punch out the rivet stem with a pin punch.
(2) Drill out the rivet head, using a drill the same size as the rivet shank.
(3) Pry off the weakened rivet head with a pin punch.
(4) Push out the remainder of the rivet shank with a punch. If the shank will not push out, drill the shank, taking care not to enlarge the hole in the material.
SELF-PLUGGING (MECHANICAL LOCK) RIVETS Self-plugging, mechanical lock rivets are similar to self-plugging, friction lock rivets, except for the manner in which they are retained in the material.
This type of rivet has a positive mechanical locking collar that resists vibration that would cause the friction lock rivets to loosen and possibly fall out (figure 5-59). Also the mechanical locking type rivet stem breaks off flush with the head and usually does not require further stem trimming when properly installed. Self-plugging, mechanical lock rivets display all the strength characteristics of solid shank rivets and in almost all cases can be Before installation After installation substituted rivet for rivet. FIGURE 5-59. Self-plugging, mechanical lock rivets.
Huck Rivets Self-plugging, mechanical lock rivets require spe- Chuck jaws cial driving assemblies. It is best to use tools manufactured by the company that produces the rivet.
The Huck CKL rivet is installed by using the Inner anvil model CP350 blind rivet tool. The nose of the tool includes: (1) A set of chuck jaws which fit the serrated grooves on the rivet stem and pull it through the rivet shank to drive the rivet; (2) an outer anvil which bears against the outer portion of the manufactured head during the driving operation; and (3) an inner anvil which advances automatically to drive the locking collar into position after the blind head is formed (figure 5-60).
A change in rivet diameter requires a change in Outer anvil chuck jaws, outer anvil, and inner thrust bearing, and an adjustment of the shift operating pressure.
Adjustment procedures are specified by the manu- - Air inlet bushing facturer. Pipe plug Cherrylock Rivets Cherrylock rivets are installed with a hydroshift or mechanical shift tooling system. The hydroshift system is a newer design and when available should be used in place of the mechanical system.
Cherrylock Mechanical Tooling Most existing Cherry riveters, either hand or
- Locknut or screw -Valve adjusting screw FIGURE 5-60. Huck model CP350 rivet pull tool.
power operated, may be used to install Cherrylock rivets when equipped with the proper mechanical pulling head.
types: the H615 (figure 5-61) and H640 (figure Cherrylock mechanical pulling heads are of two DIAMETER PULLING HEAD NUMBER DIMENSIONS 5-62) series. They differ only in their method of 3/32" H681-3€ / Universal Head .188 346 attachment to the riveter. The H615 series is for H681-4C / Universal Hea ( Countersunk Heat .163 .331 _359 the smaller screw-on type tools and the H640 is for H681-B166-4 Uni-Sink Head I Countersunk Hea 250 install bulbed and wiredraw Cherrylock rivets. the larger clip-on type. Both pulling heads will 5/38" H681-B166-5 Uni-Sink Head +68)-SC {Countersunk Hea rUnwersal Hea 313 .313 .269 M681-5C 1 Countersunk Head Universal Head 375 .415 3716" 335 H681-8166-6 Uni-Sink Head 375 .419 1/9 MGB1-BC Countersunt Head .458 .500 452 398 FICURE 5-63. H681 Series pulling head tool.
RIVET Cherrylock Hydroshift Tooling DIAMETER PULLING HEAD NUMBER The hydroshift tooling system is an advanced 1/8' H615-4C | Countersunk Hea Universal Head design in which the sequence of operations neces- sary to install the rivet is accomplished hydraulic- H615-4S Uni-Sink Head ally within the hydroshift tool rather than by means 5/32' H615-5C% Countersunk Hea ¿ Universal Head of a mechanical pulling head Cherrylock hydroshift pulling heads are of one H615-5S Uni-Sink Head type only, the H681 (figure 5-63).
3/16" 1615-6C1 Countersunk Heal Universal Head stall each diameter Cherrylock rivet. A separate H681 pulling head is required to in- Separate H615-6S Uni-Sink Head pulling heads are recommended for universal and countersunk head rivets but countersunk pulling FIGURE 5-61. H615 Series pulling head tool. heads may be used for both styles.
A separate pulling head is required to install each diameter Cherrylock rivet. Separate pulling heads are recommended for universal and countersunk head rivets but countersunk pulling heads may be used, for both styles.
Hydroshift riveters are factory adjusted to break the rivet stem flush and set the collar properly. Fine adjustments to the shift point setting can be made by the operator. This adjustment determines the flushness of the break of the rivet stem (figures 5-64 and 5-65).
Installation Procedures Procedures for installing self-plugging (mechanical lock) rivets are basically the same as those used for installing the friction lock type of rivets. Precautions to be observed are:
(1) Be sure the correct grip range is selected.
DIAMETER RIVET PULLING HEAD NUMBER 1/8" 1640-4CL Countersunk Hea universal neat H640-4S Uni-Sink Head 5/32' H640-5C1 Countersunk Head • Universal Head H640-5S Uni-Sink Head 3/16" 1640-5C1 Countersunk Hea nonversa, Heat Adjuster Knob H640-6S Uni-Sink Head 1/4" H640-8C1 Countersunk Hear Universal Head Limit Pin FIGURE 5-62. H640 Series pulling head tool. FIGURE 5-64. H681 pulling head adjuster.
1 File a small flat on rivet head Note Do steps 1, 2, and 3 only if rivet is in a thin or resilient material.
2 Centerpunch flat 3 Drill off tapered portion of pin which forms the lock 4 Shear lock by driving out pin FIGURE 5-65. Hydroshift pulling tool.
(2) Always use the correct nose assembly or pulling tool for the diameter rivet selected.
(For the CKL rivet, check the tool air 5 Pry out remainder pressure for the correct setting.) of locking collar
(3) When inserting the rivet in the tool and the material, hold a slight pressure against the head of the rivet.
(4) Determine that the rivet is completely driven before lifting the tool from the 6 Drill almost rivet head. (The stem should snap.) through rivet head
(5) Check each rivet after the driving sequence has been completed for proper 7 Pry off stem breakage. (The rivet stem should rivet head snap off even with the head of the rivet.)
Inspection Visual inspection of the seating of the pin in the.
manufactured head is the most reliable and simplest means of inspection for mechanical lock rivets. If the proper grip range has been used and the locking collar and broken end of the stem are approximately flush with the manufactured head, the rivet 8 Tap shank out with pin has been properly upset and the lock formed. Insufficient grip length is indicated by the stem breaking below the surface of the manufactured head. Excessive grip length is indicated by the stem breaking FIcURE 5-66. Rivet removal.
off well above the manufactured head. In either case, the locking collar might not be seated properly, thus forming an unsatisfactory lock.
Removal Procodures The mechanical lock rivet can easily be removed by following the procedures illustrated in figure
5-66.
PULL-THRU RIVETS squeezed, and the mandrel crank is turned clockwise after each stroke. Continue squeezing the handle and turning the mandrel crank of the heading tool until you feel a solid resistance, indicating that the rivet is set.
Mandrel crank This type of blind mechanically expanded rivet is used as a tacking rivet to attach assemblies to hollow tubes, and as a grommet. It differs from the two previously discussed rivets in that the stem pulls completely through the sleeve of the rivet during installation. Pull-thru rivets are structurally weak Movable because of the hollow center after installation is handle completed. Methods and procedures for installation, inspection, and removal are not discussed here because of the limited use for this type rivet in the airframe field. Figure 5-67 illustrates a typical pull-thru rivet before and after installation.
Threaded mandrel FIGURE 5-68. Rivnut heading tool.
Before installation After installation FIGURE 5-67. Pull-thru rivet.
RIVNUTS Rivnut is the trade name of a hollow blind rivet made of 6053 aluminum alloy, counterbored and threaded on the inside. Rivnuts are installed by one person using a special tool which heads the rivet on the blind side of the material (figure 5-68). The Rivnut is threaded on the mandrel of the heading tool and inserted in the rivet hole. The heading tool is held at right angles to the material; the handle is All Rivnuts, except the thin head (0.048 in.)
countersunk type, are available with or without small projections (keys) attached to the head to keep the Rivnut from turning. Keyed Rivnuts are used for service as a nut plate, whereas those without keys are used for straight blind riveting repairs where no torque loads are imposed. A keyway cutter is needed when installing Rivnuts which have keys (figure 5-69).
Tools used in the installation of Rivnuts include the hand-operated heading tools, the pneumatic power Rivnut driver, and the keyway cutter. All heading tools have a threaded mandrel onto which the Rivnut is threaded until the head of the Rivnut is against the anvil of the heading tool.
Hand-operated heading tools are made in three types: (1) Straight, (2) 45°, and (3) 90°. The pneumatic power driving tools are made in two types: (1) Lever throttle and (2) offset handle.
With the power tool, the threading, upsetting, and withdrawal or unthreading, are accomplished by compressed air through the manipulation of finger- 184
Radial dash marks Keyed Rivnut FIGURE 5-69. Keyed Rivnut and keyway cutter.
tip controls. The keyway cutter is for cutting keyways only. In some instances, the keyway cutter cannot be used because the material may be too thick. If such is the case, use a small round file to form the keyway.
The important factors to be considered in selecting Rivnuts are grip range, style of head, condition of Rivnut end, and the presence or absence of a key.
Proper grip length is the most important of these conditions. The grip range of a Rivnut can be determined from its number. For example, a 6-45 has a maximum grip of 0.45 in. Note the procedure to follow when determining the grip range. The total thickness of the sheets shown in figure 5-70 is
0.052 in. By referring to the Rivnut data chart in figure 5-70, we see that 6-75 is the grip length to choose since the maximum grip length of the preceding size (6-45) is only 0.045 in. and would be too short. The grip length of the 6-75 Rivnut actually ranges from 0.045 in., the maximum length of the preceding size (6-45), to 0.075 in., which is the maximum grip length of the 6-75 Rivnut.
The objective when installing this. type of rivet is to produce an ideal bulge on the blind side of the work without distorting any of the threads inside the Rivnut. In other words, be sure the bulge takes place between the first thread of the rivet and the lower edge of the riveted material. The space between the ideal bulge and the upper thread, where the gripping takes place, is considered the grip range.
When selecting head style, apply the same rules as for solid shank rivet application. Select key-type Rivnuts whenever screws are to be inserted, and use closed-end Rivnuts only in special places, such as sealed compartments of floats or pressurized compartments.
Drilling the holes for Rivnuts requires the same precision as for solid shank rivets. The shank of the Rivnut must fit snugly in the hole. To obtain the best results for a flathead installation, first drill a pilot hole smaller than the shank diameter of the Rivnut and then ream it to the correct size.
If keyed Rivnuts are used, cut the keyway after the hole has been reamed. In cutting the keyway, hold the keyway cutter so that it makes a 90° angle with the work. Also, cut the keyway on the side of the hole away from the edge of the sheet, especially when the Rivnut is used on the outside row. Operate the keyway cutter by inserting it in the hole and squeezing the handles.
The use of flush Rivnuts is limited. For metal which has a thickness greater than the mimum grip length of the first rivet of a series, use the machine countersink; for metal thinner than the minimum grip length of the first rivet, use the dimpling process. Do not use the countersunk Rivnut unless the metal is thick enough for machine countersinking, or unless the underside is accessible for the dimpling operation.
For a countersunk Rivnut the sheets to be joined can usually be machine countersunk. This method is preferred because the bearing surface in a dimpled hole in one sheet of average gage will normally occupy the entire gripping surface of the Rivnut, thus limiting its grip range to that of an anchored nut only.
When installing Rivnuts, among the things to check is the threaded mandrel of the heading tool to see that it is free from burrs and chips from the previous installation. Then screw the Rivnut on the mandrel until the head touches the anvil. Insert the Rivnut in the hole (with the key positioned in the keyway, if a key is used) and hold the heading tool at right angles to the work. Press the head of the 185
Flat 0.32 Head Thickness 6-45 6-75 5-10 8-45 8-75 8-10 10-45 10-75 10-100 6845 6875 68100 8B45 8B75 88100 10845 10875 10B100 6K45 6K75 6K100 8K45 8K75 8K100 10K45 1.0K75 10K100 6KB45 6KB75 6KB100 .052 10KB45 8KBA5 10KB75 8KB75 10KB100 8KB100
1.075 Max. 100°-0.48 Head Thickness 6-91 6-121 6-146 8-91 8-121 8-146 ..045 Min. 10-91 6891 10-121 68121 10-146 68146 8891 8B121 8B146 10891 108121 108146 100°-0.63 Head Thickness 6-106 6-136 6-167 8-106 8-136 8-761 10-106 10-136 10-161 68106 6B136 68161 88106 8B136 88161 108106 108136 108161 6K106 6K136 6K161 8K106 8K136 8K167 10K106 10K136 10K16!
6KB106 6KB136 6KB161 8KB106 8KB136 8KB167 10KB106 10KB136 10K8161 FIcURE 5-70. Determining Rivnut grip length.
Rivnut tightly against the sheet while slowly squeezing the handles of the heading tool together until the Rivnut starts to head over. Then release the handle, and screw the stud further into the rivnut.
This prevents stripping the threads of the Rivnut before it is properly headed. Again squeeze the handles together until the Rivnut heading is complete. Now remove the stud of the heading tool from the Rivnut by turning the crank counterclockwise.
The action of the heading tool draws the Rivnut against the anvil, causing a bulge to form in the counterbored portion of the Rivnut on the inaccessible side of the work. This bulge is comparable to the shop head on an ordinary solid shank rivet. The amount of squeeze required to head the Rivnut properly is best determined by practice. Avoid stripping the thread in the Rivnut.
The installation of a Rivnut is incomplete unless it is plugged either with one of the plugs designed for that purpose or with a screw used for attaching purposes. A Rivnut does not develop its full strength when left hollow.
Three types of screw plugs can be used: (1) The 100° countersunk screw plug, (2) the headless screw plug, and (3) the thin ovalhead screw plug.
The 100° countersunk and the headless screw plugs have either a Phillips or a Reed and Prince recess.
The oval head either has a common screwdriver slot, a Phillips, or a Reed and Prince recess. All screw plugs are made of high tensile strength SAE steel and are cadmium plated.
The same tools are used for installation of the splined Rivnut as for installation of the standard types, but the pullup stud of the heading tool must be adjusted to accommodate the longer shank.
DILL LOK-SKRUS AND LOK-RIVETS Dill Lok-Skru and Lok-Rivet are trade names for internally threaded rivets (two piece). They are used for blind attachment of such accessories as fairings, fillets, access door covers, door and window frames, floor panels, and the like. Lok-Skrus and Lok-Rivets are similar to the Rivnut in appearance and application. Lok-Skrus and Lok-Rivets, however, come in three parts and require more clearance on the blind side than the Rivnut to accommodate the barrel.
Special hand- and air-operated power tools are required for installation of Lok-Skrus. An interchangeable barrel blade fits into the blade handle and is held in place by a set screw. The barrel 186
blade has a flattened portion which fits into a slot in the end of the Lok-Skru barrel. The head driver has projections which fit into recesses in the Lok- Skru head. Head drivers and blades are interchangeable for use with various sizes and styles of Lok-Skrus.
The drilling procedure for Lok-Skrus is identical to that for common solid shank rivets. To install the Lok-Skru, insert the Lok-Skru tool so that the blade extends through the barrel slot and the driver sets firmly in the head slot. Insert the fastener in the drilled hole. Fit the ratchet handle assembly together and adjust the pawl lever for proper ratchet direction. Hold the ratchet handle stationary and turn the barrel blade handle to the left until the barrel is drawn firmly against the sheet on the opposite side. Press the tool firmly against the Lok- Skru to hold the tool blade and driver in the slots.
Stop turning the barrel handle when the Lok- Skru barrel has been drawn against the sheet. Finally, tighten by an additional quarter turn or less on the ratchet handle, drawing the head into the sheet. This time, hold the blade handle stationary while turning the ratchet handle. Test the tightness of the installation with an ordinary 8-in. screwdriver which has been ground round on the end.
Attachments are made by using the attaching screw and a regular screwdriver.
DEUTSCH RIVETS The Deutsch rivet is a high-strength blind rivet with a minimum shear strength of 75,000 p.s.i. and can be installed by one man. This rivet consists of two parts, a stainless steel sleeve and a hardened steel drive pin. The pin and sleeve are coated with a lubricant and a corrosion inhibitor.
A Deutsch rivet may be driven with an ordinary hammer or a pneumatic rivet gun and a flathead set.
Seat the rivet in the previously drilled hole and then drive the pin into the sleeve. If the Deutsch rivet is driven into a tight hole, a hollow drift punch should be used to seat the rivet against the material. The punch should clear the drive pin and rest against the head of the rivet to prevent premature expansion of the sleeve and head.
The driving action causes the pin to exert pressure against the sleeve and forces the sides of the sleeve out. This stretching forms a shop head on the end of the rivet and provides a positive fastening action for the fastener. The ridge on the top of the rivet head locks the pin into the rivet as the last few blows are struck.
The head of the Deutsch rivet should never be shaved or milled. Milling or shaving will destroy the locking action of the ring on top of the rivet head.
Another feature of the Deutsch rivet is that it can be installed without going all the way through the second piece of material. However, this type of installation is not recommended unless the second piece is very thick.
One of the main restrictions to the use of the Deutsch rivet is that no bucking tool is used to take up the shock of driving. The structure where installation is made must be heavy and solid enough to support the driving forces.
If a Deutsch rivet that extends through the material is to be removed, use the same procedures used to remove a solid shank rivet. The head can be drilled off, and the pin can be driven out with a drift punch slightly smaller than the diameter of the drive pin. To drive the sleeve out of the material, use a drive punch slightly smaller than the diameter of the sleeve.
If the rivet does not extend through the material, drill out the drive pin to approximately one-half its depth. Then tap the hole and finish drilling out the remainder of the pin. Next, insert a screw through a spacer and tighten the screw into the sleeve. Continue tightening the screw until the sleeve is removed.
HI-SHEAR RIVETS Hi-Shear pin rivets are essentially threadless bolts. The pin is headed at one end and is grooved about the circumference at the other. A metal collar is swaged onto the grooved end, effecting a firm tight fit.
The proper length rivet may be determined by part number or by trial. Part numbers for pin rivets can be interpreted to give the diameter and grip length of the individual rivets. A typical part number and an explanation of the terms are discussed in Chapter 6, Hardware, Materials, and Processes, in the Airframe and Powerplant Mechanics General Handbook, AC 65-9A.
To determine correct grip length by trial, insert the correct diameter rivet in the hole. The straight portion of the shank should not extend more than 16 in. through the material, insert the correct diameter rivet in the hole. The straight portion of the shank should not extend more than 16 in. through the material. Place a collar over the grooved end of the rivet. Check the position of the collar.