Aircraft Maintenance Sheet Metal SM1 Tools

Hand Tools

• Tools for driving and upsetting rivets: drills, bucking bars, riveting hammers, draw sets, dimpling dies/countersinking equipment, rivet guns, and squeeze riveters.
• Clecos, C-clamps, vises, and fasteners are necessary to hold sheets together when riveting.

Scales

• Scales are available in various lengths, with 6-inch and 12-inch options are the most common and affordable.
• A scale with fractions on one side and decimals on the other can be very useful.
• To obtain accurate measurements with a scale, hold it on its edge and measure from the 1-inch mark as opposed to the end

Hand Cutting Tools

• Many hand cutting tools are available to cut light gauge sheet metal.
• Four cutting tools commonly found in an air frame repair shop: Files, straight hand snips, aviation snips, deburring tools.

Files

• Files are used to shape metal by cutting and abrasion.
• Numerous sizes and shapes of files are available; common shapes include: flat, triangle, square, half round, and round.
• The teeth of the file do the cutting, and are set at an angle across the face of the file.
• Files are graded according to tooth spacing.
  • Coarse files have a small number of large teeth.
  • Smooth files have a large number of fine teeth.
• The coarser the teeth, the more metal is removed on each stroke.
• File teeth can be cleaned with a file card.

Aviation Snips

• Aviation snips are used to cut holes, curved parts, round patches, and doublers.
• Colored handles are used to identify the cutting direction.
  • Yellow aviation snips cut straight.
  • Green aviation snips cut curve right.
  • Red aviation snips cut curve left.

Straight Snips

• Straight snips (or sheet metal shears) feature straight blades sharpened to an 85° angle.
• Available in sizes ranging from 6 to 14 inches, they can cut aluminum up to 1/16 of an inch.
• Straight snips can be used for straight cutting and large curves, however aviation snips are more suitable for cutting circles or arcs.

Deburring Tool

• A deburring tool removes the burr from the edge of a sheet or a hole.

Cleco Fastener

• Reusable sheet metal fasteners temporarily hold drilled sheet metal parts accurately in position for riveting or drilling.
• Sheet metal parts separate while being riveted or drilled if they are not held tight together.
• The Cleco fastener is the most commonly used sheet metal holder.
• The re-useable Cleco fastener keeps the holes in the separate sheets aligned when installed properly
• The Cleco fastener consists of a steel cylinder body with a plunger, spring, step-cut locks, and a spreader bar
• These fasteners come in six different sizes: 3/32, 1/8, 5/32, 3/16, 1/4, and 3/8-inch with the size stamped on the fastener Color coding allows for easy size recognition, and a special type of plier fits the six different sizes

Pneumatic Drill

• Pneumatic drill motors are the most common type of drill motor for aircraft repair work.
• Pneumatic drills are lightweight, have sufficient power, and good speed control.
• Most drill motors used for aircraft sheet metal work are rated at 3,000 rpm.
• A drill motor with more torque and a lower rpm is better to prevent damage to tools and materials when drilling deep holes or drilling in hard materials like corrosion resistant steel or titanium.

Drill Bits

• Standard twist drill bits for aluminum are made from High Speed Steel (HSS) with a 135° split point.
• HSS drill bits are the industry standard for drilling metal because they stay sharper longer.
• HSS drill bits can withstand temperatures nearing the critical range of 1,400 °F (dark cherry red) without losing their hardness.
• Drill diameters are grouped by three size standards: fractional, number and letter.
• Drill bits for titanium are made from cobalt vanadium for increased wear resistance.

Pneumatic Rivet Gun

• The pneumatic rivet gun is the most common rivet tool used in airframe repair work.
• An air driven hammer inside the barrel of the gun provides force to buck the rivet.
• Available in many sizes and types, and can use interchangeable rivet sets.
• The less powerful 3X gun is used for smaller rivets in thinner structures, while 7X guns are used for large rivets in thicker structures.
• Slow hitting rivet guns that strike from 900 to 2,500 blows per minute are the most common type.
• Rivet guns should upset a rivet in 1 to 3 seconds.

Using Pneumatic Rivet Gun

• The correct rivet set and the retaining spring must always be installed.
• The driving force of the rivet gun can be adjusted by a needle valve on the handle.
• A gun that's too powerful is hard to control and may damage the work, and conversely, a gun that is too light may work harden the rivet before the head can be fully formed.
• The rivet gun should be tested on a piece of wood, and adjust the air valve to a setting that is comfortable.
• Adjustments should never be tested against anything harder than a wooden block to avoid set damage.
• A different sized gun is needed if the adjustment fails to provide the best driving force.
• The riveting action should start slowly and be one continued burst.
• If the riveting starts too fast, the rivet header might slip off the rivet and damage the rivet (smiley) or damage the skin (eyebrow).
• Drive the rivets within 3 seconds so the rivet won't work harden if the driving process takes too long.
• Precautions to be observed when using a rivet gun:
  • Never point a rivet gun at anyone.
  • Never depress the trigger unless the set is held tightly against a block of wood or a rivet.
  • Always disconnect the air hose when it is not in use for any appreciable length of time.

Pneumatic Rivet Gun Set

• Pneumatic guns are used in conjunction with interchangeable rivet sets, or snaps.
• Rivet sets are made in a variety of styles.
• A set must be the correct match for the rivet being driven.

Rivet Sets

• The working face of a set should be properly designed and smoothly polished.
• They are made of forged steel, heat treated to be tough but not too brittle.
• Rivet sets should be kept clean.
• Nonflush sets should fit to contact about 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 is designed to fit the specific type of rivet and the location of the work.
• The short, straight set is best when the gun can be brought close to the work.
• Long sets are sometimes necessary when the gun cannot be brought close to the work due to structural interference.
• Offset sets may be used to reach rivets in obstructed places.
• Flush sets come in various sizes.
  • Smaller flush sets concentrate driving force in a small area for maximum efficiency.
  • Larger flush sets spread driving force over a larger area, and are used for riveting thin skins.

Bucking Bars

• The bucking bar, is a heavy chunk of steel that counters vibration during rivet installation.
• They come in a variety of shapes and sizes, between a few ounces to 8 or 10 pounds depending on the work.
• Bucking bars must be hard enough to resist indentation, but not hard enough to shatter.
• Their edges should be slightly rounded to prevent marring the material, and the bucking faces must be kept clean, smooth, and well polished.
• Ensure that the bucking bar has the correct shape and weight for the job.
  • A bar that is too light won't give the necessary bucking weight.
  • A bar that is too heavy risks excess force and bulging the material.

Using Bucking Bars

• Always hold the face of the bucking bar at right angles to the rivet shank. Failing to do so causes the rivet shank to bend.
• Maintain bucking bar position until the rivet is completely driven.
• The weight of the bucking bar should do most of the work. The operator's hands merely guide the bar and supply required tension and rebound action.
• Defective rivet shop heads can be caused by:
  • Failure to hold the bucking bar at right angles to the rivet.
  • Removing the bucking bar while the gun is in operation.

Compression Riveting

• Compression (squeezing) is a quick riveting method requiring only one operator, but can only be used over edges of sheets/assemblies.
• Compression can only be used providing the rivet squeezer's reach is deep enough.
• The compression riveting process involves one stationary jaw acting as a bucking bar, while the other is movable to upset the rivet.
• There are three types of rivet squeezers: hand, pneumatic, and pneudraulic. All operate on the same principles.
  • Hand rivet squeezer's compression is supplied by hand pressure.
  • Pneumatic rivet squeezer's compression is supplied by air pressure.
  • Pneudraulic rivet squeezer's compressions are supplied by a combination of air and hydraulic pressure.

Countersinking Tool

• The countersink cuts a cone-shaped depression around the rivet hole allowing the rivet to sit flush with the surface of the skin.
• Countersinks are made with angles to correspond with various angles of countersunk rivet heads.
• A standard countersink has a 100° angle.
• Microstop countersinks are adjustable to any depth, and have cutters allowing interchangeable holes with various countersunk angles.
  • Some stop countersinks feature a micrometer set mechanism, in 0.001-inch increments, for adjusting the cutting depths.

Dimpling Dies

• Dimpling uses a male and female die (punch and die set).
• The male die has a guide the size of the rivet hole, and with the same degree of countersink as the rivet.
• The female die has a hole with a corresponding degree of countersink in which the male guide fits.

Microshaver

• A microshaver is used if the smoothness of the material (such as skin) requires that all countersunk rivets be driven within a specific tolerance, and has a cutter, stop and two legs/stabilizers.
• The cutting portion is inside the stop.
• Pull outwards on the stop and turn it in either direction to adjust the cut depth as needed, clockwise for deeper cuts.

Shop Tools

• Shop tools are usually in a fixed location because of their size, weight, and/or power source.
• The airframe part to be constructed or repaired is brought to the tool.

Squaring Shear

• The squaring shear provides the airframe technician with a convenient means of cutting and squaring sheet metal.
• It is available as: manual, hydraulic, or pneumatic model.
• This shear has a stationary lower blade attached to a bed and a movable upper blade attached to a crosshead
• Placed on the bed are two squaring fences, consisting of thick strips of metal to form a 90° angle with the blades so that squaring metal sheets can be performed.
• A scale graduated in fractions of an inch is scribed on the bed.
• To make a cut with a foot shear, move the upper blade down utilizing the foot to step on the treadle and push downward.
• Springs raise the blade and treadle once the metal is cut and pressure from the foot is removed.
• Hydraulic and pneumatic models utilize remote foot pedals to ensure operator safety.
• In order to cut to a line, place the sheet on the bed of the shears in front of the cutting blade with the cutting line even with the cutting edge of the bed
• To cut the sheet with a foot shear, step on the treadle while holding the sheet securely in place.
• The metal cutting capacity of foot-operated shears is 0.063 inch of aluminum alloy. Use powered squaring shears for cutting thicker metals.
• Hydraulic or pneumatic models utilize remote foot pedals to ensure operator safety.

Bending Break

• Ordinary bends with the bending brake involves placing the sheet on the bed with the sight line directly under the edge of the nose.
• The clamping bar is brought down to hold the sheet firmly in place.
• The bending leaf is raised until the proper angle is achieved.
• If other bends are to be made, the clamping bar is lifted and the sheet is moved.
• Most metals have a tendency to return to their normal shape, a characteristic known as spring-back.
• If the bending brake is set for a 90° bend, the metal bent probably forms an angle of about 87° to 88°.
• To achieve a bend of 90°, set the cornice brake to bend an angle of about 93° to allow for spring-back

Rotary Punch Press

• Used to punch holes in metal parts, the rotary punch can cut radii in corners, make washers, and perform other jobs needing holes.
• Composed of two cylindrical turrets mounted over each other, which must be synchronized to work properly.
• Index pins ensure correct alignment of the punch and dies.
• The levers on the machine may be moved to release alignment by withdrawing index pins from their locked position
• The operator may turn the turrets to the desired punch size.
• Mechanical locking devices will release because tapered index locking pins will seat to prevent punching until the turrets are aligned.
• To operate the machine, place the metal to be worked between the die and punch.
• Pull the lever on the top of the machine to force the punch through the metal.
• When the lever is returned to its original position, the metal is removed.
• The diameter of each punch is stamped on the front of its die holder.
• Place each punch's centered point in the center punch in order to punch the hole in the correct location.