Sheet Metal #1 Tools: Aircraft Hand Tools and Measuring

Hand Tools

• Tools include drills, bucking bars, riveting hammers, draw sets, dimpling dies, countersinking equipment, rivet guns, and squeeze riveters
• Clecos, C-clamps, vises, and fasteners help hold sheets together during riveting

Scales

• Scales come in various lengths, with 6-inch and 12-inch being most common and affordable
• A scale with fractions on one side and decimals on the other can be very useful
• For accurate measurements, measure from the 1-inch mark, not the end, while holding the scale on its edge

Hand Cutting Tools

• Files, straight hand snips, aviation snips, and deburring tools are common in airframe repair shops

Files

• Files shape metal through cutting and abrasion
• Files come in flat, triangle, square, half round, and round shapes
• The teeth do the cutting and are angled across the file's face
• Files are graded by tooth spacing
  • Coarse files have fewer, larger teeth
  • Smooth files have many, fine teeth
• Coarser teeth remove more metal per stroke
• A file card cleans file teeth

Aviation Snips

• Aviation snips cut holes, curves, round patches, and doublers in sheet metal
• Colored handles indicate cutting direction
  • Yellow snips cut straight
  • Green snips curve right
  • Red snips curve left

Straight Snips

• Straight snips, or sheet metal shears, have straight blades sharpened to 85°
• Available in 6-14 inch sizes, they cut aluminum up to 1/16 inch thick
• Straight snips are for straight cuts and large curves, aviation snips are better for circles/arcs

Deburring Tool

• Deburring tools remove burrs from sheet edges or deburr holes

Cleco Fastener

• Reusable fasteners temporarily hold drilled sheet metal parts for riveting/drilling
• They prevent separation of parts
• The fasteners consist of a steel cylinder body with a plunger, spring, step-cut locks, and a spreader bar
• Fasteners sizes include 3/32, 1/8, 5/32, 3/16, 1/4, and 3/8-inch diameters
• Color coding provides easy size recognition
• Pliers are available for the all six sizes

Pneumatic Drill

• Pneumatic drills are common for aircraft repair
• They are lightweight, with good power and speed control
• Most drill motors for sheet metal work are rated at 3,000 rpm
• Lower rpm and higher torque are needed for drilling deep holes or hard materials like steel or titanium to prevent damage

Drill Bits

• Standard twist drills for aluminum are HSS with a 135° split point
• HSS drills are the industry standard because they stay sharper longer
• HSS bits withstand temperatures near 1,400 °F without losing hardness
• The three drill diameter size standards include Fractional, Number, and Letter
• Bits for titanium are made from cobalt vanadium for increased wear resistance

Pneumatic Rivet Gun

• Pneumatic rivet guns are common in airframe repair
• An air-driven hammer inside supplies force to buck the rivet
• They are available in many sizes and types, and also use interchangeable rivet sets
• 3X guns are less powerful and used for smaller rivets in thinner structures
• 7X guns are used for larger rivets in thicker structures
• Slow-hitting rivet guns strike from 900 to 2,500 blows per minute which are common
• A rivet gun should upset a rivet in 1 to 3 seconds
• Correct rivet sets and retaining springs must be installed
• A needle valve adjusts the driving force
• A gun that is too powerful is hard to control and damages work
• If the gun is too light, it work hardens rivets
• Test the rivet gun on wood, and adjust the air valve to be comfortable for the operator
• Adjustments should never be tested on anything harder than a wooden block to avoid set damage
• A different-sized gun is needed if an adjustment fails to provide the best driving force
• Riveting action should start slowly and have one continued burst
• The rivet header can slip off and damage the rivet/skin if riveting starts too fast
• Rivets driven in 3 seconds, it will work harden if the driving process takes too long
• Riveting involves opposing blows that squeeze the rivet, swelling it and forming the upset head
• Never point a rivet gun at anyone
• Rivet guns should only be used to drive/install rivets
• Never depress the trigger unless the set is securely against a block of wood or a rivet
• Disconnect the air hose when the rivet gun is not in use

Rivet Gun Sets

• Pneumatic guns are used with interchangeable rivet sets/snaps
• Rivet sets are made in a variety of styles
• An appropriate set must be a correct match for the rivet being driven
• The working face of a set should be properly designed and smoothly polished
• They're generally made of forged steel, heat treated to be tough but not too brittle
• Sets should be kept clean
• Nonflush sets should contact the center two-thirds of the rivet head
• A set that is too small marks the rivet, while one too large marks the material
• Each set fits the specific rivet type and work location
• Short, straight sets work best when the gun is close to the work
• Long sets are needed when structural interference prevents close access
• Offset sets reach rivets in obstructed places
• Flush sets come in various sizes
  • Smaller sets concentrate driving force for efficiency
  • Larger sets spread driving force for riveting thin skins

Bucking Bars

• Bucking bars, sometimes called a dolly, or bucking iron, are a heavy chunk of steel that counter vibration
• Bucking bars range from a few ounces to 8-10 pounds, depending on the work
• Bucking bars must be hard enough to resist indentation but not too hard
• Bucking bar edges should be slightly rounded to prevent marring/damage
• Bucking faces must be kept clean, smooth, and well polished
• Shape is the first consideration when selecting a bucking bar
• The weight should be considered, too light will not give the necessary bucking weight
• If the bar is too heavy it will bulge the shop head
• Always hold the face of the bucking bar at right angles to the rivet shank
• Failure to hold the face of the bucking bar at right angles to the rivet shank causes the rivet shank to bend and mar the final blows
• The bucker must hold the bucking bar in place until the rivet is completely driven
• Let the weight of the bucking bar do most of the work
• An operator's hands merely guide the bar and allow tension and rebound action
• Defective rivet shop heads may be caused by failure to hold the bucking bar at right angles to the rivet
• Defective heads may also be caused if the bucking bar is removed while the gun is in operation

Compression Riveting

• Compression riveting uses a squeezer for a quick, single-operator method
• Compression riveting can only be used over the edges of sheets/assemblies, given proper conditions and squeezer reach
• One jaw is stationary (bucking bar), the other is movable and does the upsetting
• The three types are hand, pneumatic, and pneudraulic
• They all operate on the same principles

Compression Riveting Types

• Hand rivet squeezers use hand pressure
• Pneumatic rivet squeezers use air pressure
• Pneudraulic rivet squeezers mix air and hydraulic pressure

Countersinking Tool

• A countersink cuts a cone-shaped depression around the rivet hole, letting the rivet sit flush with the skin
• Countersinks match the angles of countersunk rivet heads
• The standard countersink has a 100° angle
• Microstop countersinks, or stop countersinks, can be adjusted for depth and have cutters for different countersunk angles
• Some stop countersinks have a micrometer set mechanism, in 0.001-inch increments, that adjust cutting depths

Dimpling Dies

• Dimpling uses a male and female die, which is a punch and die set
• The male die has a rivet hole guide and the same countersink degree as the rivet
• The female die has a hole with a matching countersink degree to fit the male guide

Microshaver

• Microshavers ensure countersunk rivets are within a specific tolerance, and for smoothness on materials like skin
• A microshaver has a cutter, a stop, and two legs/stabilizers
• The cutter is inside the stop
• Adjust the cutting depth by pulling out the stop and turning in either direction (clockwise for deeper cuts)

Shop Tools

• Shop tools stay in a fixed location due to size, weight, and/or power source where the airframe part to be constructed or repaired is brought to the tool

Squaring Shear

• Squaring shears help airframe technicians in cutting and squaring sheet metal
• Squaring shears are available as manual, hydraulic, and pneumatic models
• A shear consists of a stationary lower blade attached to a bed and a movable upper blade attached to a crosshead
• Two squaring fences (thick metal strips) square metal sheets; one on the right and one on the left to form a 90° angle with the blades
• A scale graduated in fractions of an inch is scribed on the bed
• Foot shears cut by placing the foot on the treadle and pushing downward
• A spring raises the blade and treadle once the metal is cut and foot pressure is removed
• Hydraulic/pneumatic models use remote foot pedals for operator safety
• Shears cutting to a line, place the sheet to cut line even with the cutting edge of the bed
• To cut sheets securely with footshear, step on the treadle
• Foot-operated shears have a 0.063 inch maximum aluminum alloy cutting capacity
• Powered shears should be used for thicker metals
• Hydraulic and pneumatic models use remote foot pedals for operator safety

Bending Break

• Bending breaks bend sheets: place the sheet with the sight line (bend mark) under the nose's edge
• Bending breaks clamp the bar to hold the sheet firmly
• Raise bending leaf to the proper angle
• If other bends, lift the clamping bar and move sheet to the correct position for its bending
• Spring-back occurs as most metals tend to return to their normal shape
• If the bending brake is set for a 90° bend, the metal bent probably forms an angle of about 87° to 88°
• If a bend of 90° is desired, set the cornice brake to bend an angle of about 93° to allow for spring-back

Rotary Punch Press

• Rotary punch press punches holes in metal parts for airframe repair shops
• Rotary punch press can cut cut radii in corners, make washers, and perform many other jobs that require holes
• Rotary punch press has two cylindrical turrets with dies that must be synchronized
• Index pins ensure alignment of punch and dies and will be released for movement by levers on the machine
• Removing the index pins will also release the mechanical locking device
• Operation includes placing the metal between the die and punch
• Pull the lever on the top of the machine toward the operator, forcing the punch through the metal
• When the lever is returned to its original position, the metal is removed from the punch
• The diameter of the punch is stamped on the front of each die holder
• Each punch has a point in its center that is placed in the center punch mark to punch the hole in the correct location