Sheet Metal Bending Tools PDF

Sheet Metal Bending Tools Sheet Metal Bending Very few sheet metal aircraft skins are perfectly flat. In fact, nearly all require bends or curves that must be shaped in some manner. Forming or bending tools include tools that create straight bends as well as those that create compound...

Sheet Metal Bending Tools Sheet Metal Bending Very few sheet metal aircraft skins are perfectly flat. In fact, nearly all require bends or curves that must be shaped in some manner. Forming or bending tools include tools that create straight bends as well as those that create compound curves. Some of these tools are manually powered, while others are electrically, pneumatically or hydraulically powered. The easiest and most accurate method of bending sheet metal is with folding machines. These machines include: Press brake Cornice brake Bar folding machine Box brake. Sheet metal bending machine 2023-11-16 B1-07d Maintenance Practices Page 83 of 335 CASA Part Part 66 - Training Materials Only  Press Brake With press brakes, a female die is fixed and a male die is driven by energy stored in a heavy flywheel by an electric motor. They are primarily used in repetitive aircraft and commercial production work. The material is moved over the female die until it rests against the stop and the male die is lowered into it. As the dies come together, they form an accurate bend that can be duplicated many times. Press brake The number and types of dies available allow press brakes to be used for almost any kind of sheet metal bend. They are good for economical mass production. A skilled worker sets up the machine to allow semi-skilled production workers or even robots to produce the sheet metal parts. 2023-11-16 B1-07d Maintenance Practices Page 84 of 335 CASA Part Part 66 - Training Materials Only  Press brake dies in use Cornice Brake Cornice brakes can bend large sheets of metal and accommodate a wide range of metal thicknesses.They have a range of standard capacities for mild steel sheet, from 12 to 22 gauge (0.110 in. to 0.032 in.) and 3 to 12 ft wide. A cornice brake 2023-11-16 B1-07d Maintenance Practices Page 85 of 335 CASA Part Part 66 - Training Materials Only  They have a sharp nose bar, around which bars of any radius may be placed. Other parts include the bed which, with the clamping nose bar, holds the job in place and the bending leaf which forms the material around the nose bar/radius block. The clamping nose bar is adjustable to facilitate different thicknesses of material and is actioned by a handle to clamp. © Aviation Australia The action of a cornice brake The bending leaf is adjustable to facilitate different radii and is counterweighted to aid the operator in bending. The higher the bending leaf is raised, the larger the angle. Generally, it is necessary to bend metal past the desired angle to allow for spring-back. Radius bars are tapered to allow greater bending angles. When using radius bars, a sight line is required one radius from the bend line. © Aviation Australia Positioning the sight line 2023-11-16 B1-07d Maintenance Practices Page 86 of 335 CASA Part Part 66 - Training Materials Only  Bar Folder A bar folder is used to bend edges of light material. It has a capacity of up to 22 gauge thick and 42 in. in length. Adjustment screws at each end of the machine are provided to adjust material thickness. A bar folder The Box Brake The box brake is also called a pan brake or finger brake. It is similar to the cornice brake except that its top leaf has removable fingers. It allows boxes to be fabricated, hence the name. Its fingers are adjusted to fit between two sides of a partially formed box, and it allows folding of the adjacent sides. At least 75% of the leaf should be fitted when bending metal with this machine. A box or pan brake 2023-11-16 B1-07d Maintenance Practices Page 87 of 335 CASA Part Part 66 - Training Materials Only  Folding Machine Safety Precautions The following precautions must be observed in order to prevent personal injury and damage to equipment: Keep fingers and other body parts clear of clamping jaws. Keep clear of counterweights attached to clamping jaw and bending leaves. Ensure communication is clear when two or more people are operating. Ensure the machine is set correctly prior to use. Do not fold anything other than sheet metal or plastic in folding machines. Keep all metal parts lightly oiled to prevent rust. A well-maintained machine is a safe and accurate machine. Folding machine safety precautions 2023-11-16 B1-07d Maintenance Practices Page 88 of 335 CASA Part Part 66 - Training Materials Only  Shrinking and Stretching Machines Shrinking and stretching machines are used to form contours by expanding or compressing metal. A stretcher expands the metal’s edge to form an outside curve, while a shrinker contracts the metal to form an inside curve. Both tools are similar in that they have two sets of gripping jaws operated by hand lever or foot pedal. Shrinking and stretching machine Shrinker – jaws grip metal and move inwards, compressing the edge Stretcher – jaws grip and spread metal apart. The progressive working of metal over a certain distance will curve it. The jaws move the metal just enough to compress or stretch it without buckling or tearing. They can be hand operated or power operated, like this Piccolo®. 2023-11-16 B1-07d Maintenance Practices Page 89 of 335 CASA Part Part 66 - Training Materials Only  Using a Piccolo machine Bumping and Hand Forming Bumping and hand forming are the methods used to form compound curves in angles, channels, ribs and non-structural streamlined fairings. Extruded angles can be convex or concave. They are curved by bumping metal with a wooden or plastic mallet around a hardwood block. Hand forming using a mallet 2023-11-16 B1-07d Maintenance Practices Page 90 of 335 CASA Part Part 66 - Training Materials Only  A concave curve can be formed into an angle by shrinking the flange over a hardwood V-block. Hand forming using a mallet and V-block Compound curved channels can be formed by using two hardwood blocks clamped in a vice. The material is formed with a mallet over a radius block that has been constructed to the correct size and shape specifications. Forming a compound curved channel using hardwood radius blocks 2023-11-16 B1-07d Maintenance Practices Page 91 of 335 CASA Part Part 66 - Training Materials Only  When forming compound curves, metal should be backed with a hardwood forming bar for better control of the bend. Using a hardwood forming bar to provide better bend control Ensure the radius block has provision for material spring-back. Finish the bend using a mallet and a block of wood. Using a mallet and hardwood block to finish the bend 2023-11-16 B1-07d Maintenance Practices Page 92 of 335 CASA Part Part 66 - Training Materials Only  Many components and structures can be formed using hand shrinking and stretching (bumping). For example, several different versions of nose ribs can be formed using these methods. Different nose ribs formed by bumping Non-structural streamline fairings may be hand formed in a wooden female forming block. A hold- down plate is used to hold the material, and a mallet is used to stretch the material into the form. If the material ‘work hardens’ during the bumping process, it will need to be annealed again. The fairing is then trimmed to its finished size. 2023-11-16 B1-07d Maintenance Practices Page 93 of 335 CASA Part Part 66 - Training Materials Only  Non-structural parts can be manufactured using hardwood dies Compound curves can also be formed by using a wooden or plastic mallet over a leather lead or steel shot-filled bag. Compound curves can be formed using a mallet and shot-bag 2023-11-16 B1-07d Maintenance Practices Page 94 of 335 CASA Part Part 66 - Training Materials Only  Joggles Joggles are used to overlap pieces of metal so the surface is flat on one side, for example, where a repair doubler is to fit over an angle. The end of one piece is bent just enough to clear the other, then bent back to parallel. Parts should be joggled to fit rather than pulled in with rivets. A joggled doubler fits neatly over a stringer Methods of joggling include: Pressing metal to shape using metal dies Forming in a metal brake. Forming a joggle using a press and metal dies 2023-11-16 B1-07d Maintenance Practices Page 95 of 335 CASA Part Part 66 - Training Materials Only  Roll Formers Rollers are used to put gentle curves in sheet metal. The machine consists of three hard steel rollers in a framework. One is the drive roller, operated by a crank handle. An adjustable clamp roller aids in pulling metal through. The radius roller can be adjusted in or out to increase or decrease radius. Rollers can also be adjusted ‘out of parallel’ to enable a cone shape to be rolled. Rollers are used to form curves in metal To use a roll former, place the metal between the drive and clamp rollers and crank it through a number of times, each time adjusting the radius. For safety: Keep fingers and clothing clear. Roll wire/rod only in the slots provided. Keep the rollers lightly oiled. 2023-11-16 B1-07d Maintenance Practices Page 96 of 335 CASA Part Part 66 - Training Materials Only  Presses Presses are used in aircraft manufacture to produce many components, from small stampings to large compound curved skins. Hydropress Hydropresses are used for smaller compound curved parts. A blank is placed over a metal male die and held in place with pins. The die is placed on the hydropress, a rubber-covered ram is lowered over the die and water pressure is applied to shape the part. A part manufactured in a hydropress 2023-11-16 B1-07d Maintenance Practices Page 97 of 335 CASA Part Part 66 - Training Materials Only  Sheet Metal Cutting Tools Shears Cutting sheet metal is performed using hand or machine shears. Hand shears include: Aviation snips Tin snips. In the aircraft workshop, shears are primarily used for notching out corner material to facilitate folding. Tin snips (top) and colour-coded Aviation snips 2023-11-16 B1-07d Maintenance Practices Page 98 of 335 CASA Part Part 66 - Training Materials Only  Treadle Guillotine A treadle guillotine is used to cut flat sheet metal stock; it has a foot-operated blade. It is also known as a squaring shear and comes in different widths and material cutting capacities. A treadle guillotine 2023-11-16 B1-07d Maintenance Practices Page 99 of 335 CASA Part Part 66 - Training Materials Only  Squaring Shears Squaring shears have side fences as guides to enable a square cut. They also have an adjustable stop fence for setting the depth of cut and incorporate a clamp to hold the job tight. Stepping on the treadle clamps the metal, and the blade cuts the metal smoothly with a minimum of burrs. For safety: Keep fingers clear of the clamp and blade. Keep the shears lubricated. Squaring shears 2023-11-16 B1-07d Maintenance Practices Page 100 of 335 CASA Part Part 66 - Training Materials Only  Power Guillotine A power guillotine is used to cut wider and thicker flat sheet metal stock than is possible with the treadle guillotine or squaring shears. It is foot operated and power assisted by: Flywheel inertia. Hydraulic power. Power Guillotine Note the foot-operated pedal and control panel. 2023-11-16 B1-07d Maintenance Practices Page 101 of 335 CASA Part Part 66 - Training Materials Only  Throatless Shears Throatless shears are a hand-operated tool which allows more mobility in cutting as there is no obstruction due to the design of the shears. Metal of any length and any shape can be cut quite easily. They have the same cutting action as a pair of scissors. Throatless shears 2023-11-16 B1-07d Maintenance Practices Page 102 of 335 CASA Part Part 66 - Training Materials Only  Scroll Shears Scroll shears are used to make irregular cuts on the inside of a sheet without cutting through the edge. The upper blade is stationary while the bottom blade is operated upwards by a handle. It has the same cutting action as a can opener. Scroll shears 2023-11-16 B1-07d Maintenance Practices Page 103 of 335 CASA Part Part 66 - Training Materials Only  Sheet Metal Working Sheet Metal Layout In order to manufacture a sheet metal item accurately, you need to consider the physical changes that occur inside the metal when bending. To finish with the correct size component after bending, you need to know how much material will be used to form the bend. This is done by calculating the bend allowance and adding it to the overall dimension. To calculate the bend allowance, you need to know the following: Bend radius Material thickness Bend angle Neutral axis Mould line and mould point Bend tangent line Flats Setback. Flat Panel 2023-11-16 B1-07d Maintenance Practices Page 104 of 335 CASA Part Part 66 - Training Materials Only  Bend Radius The bend radius (BR) is the amount of curve on the inside of the bend. In general sheet metal bending, the BR is usually quite tight. When bending hard metals like tempered aircraft aluminium alloys, sharp bends need to be avoided as the metal will crack. Bend radius Minimum Bend Radius The minimum BR is used to prevent tempered metals from cracking. Minimum BR charts are available to assist in choosing a bend allowance for material type and thickness. A minimum bend radius chart 2023-11-16 B1-07d Maintenance Practices Page 105 of 335 CASA Part Part 66 - Training Materials Only  Material Thickness and Bend Angle The bend angle is the angle at which the metal is bent. The material thickness (MT) is the thickness of the metal to be bent. Bend angle and material thickness Neutral Axis During bending, the outside of the metal stretches while the inside compresses. A portion within the metal that neither shrinks nor stretches is called the neutral axis. The neutral axis is not exactly in the middle of the sheet. It is located at about 44.53% of the MT, measured from the inside of the bend. The neutral axis 2023-11-16 B1-07d Maintenance Practices Page 106 of 335 CASA Part Part 66 - Training Materials Only  Setback For bends greater or less than 90°, the SB (setback) will be different. Therefore it is necessary to apply an additional multiplier to the SB formulae, known as the K-value. The SB formulae now becomes: SB = K (BR + M T ) For a 90° bend, the K-value is 1. Setback 2023-11-16 B1-07d Maintenance Practices Page 107 of 335 CASA Part Part 66 - Training Materials Only  K Value K charts are available for determining the K value for given angles. If a K chart is not available, then use: K = Tangent of half of the Bend Angle For example, for a 60° bend, the K-value is: K60° = tan 30° = 0.5773 A K Chart 2023-11-16 B1-07d Maintenance Practices Page 108 of 335 CASA Part Part 66 - Training Materials Only  Setback Examples Calculate the setback for the three angles shown in the illustration. Discuss your answers with your instructor when finished. Setback calculations Setback Answers Setback calculation - 90° bend 2023-11-16 B1-07d Maintenance Practices Page 109 of 335 CASA Part Part 66 - Training Materials Only  Setback calculation - open angle Setback calculation - closed angle 2023-11-16 B1-07d Maintenance Practices Page 110 of 335 CASA Part Part 66 - Training Materials Only  Flat The flat is the portion of the metal that is not bent. It is the distance between: The bend tangent lines (BTLs) or The BTL and the edge of the metal. Flats 2023-11-16 B1-07d Maintenance Practices Page 111 of 335 CASA Part Part 66 - Training Materials Only  Calculating the Flat You are to fabricate a channel from 0.040-in. 2024-T3, 3 in. wide with 90° sides, and a bend radius of 1/8 in. From this instruction we know the following: The material thickness (MT) needs to be 0.040 inches. The bend radius (BR) must be 1/8 inches (0.125 inches). You are fabricating a channel (i.e. two sides) and these sides must be 90° (perfectly vertical). To lay out the pattern on sheet metal, we need to know the true length of the flat. For this channel, the flat will be the width (3 in.) minus two setbacks (one for each side). First, calculate the setback: Sheet metal calculation task SB 90° = K(BR + M T ) = 1(0.125 + 0.040 in. ) = 0.165 in. Now, to calculate the flat, subtract the two setbacks from the width: F lat = 3 in. − (2 × 0.165 in. ) = 3 in. − 0.330 43 = 2.67 in. = 2 in. 64 2023-11-16 B1-07d Maintenance Practices Page 112 of 335 CASA Part Part 66 - Training Materials Only  Bend Allowance The flat is one of the two measurements required for a flat pattern layout. The other is called the bend allowance (BA). The BA is the amount of material actually consumed in forming the bend. It is equal to the length of the neutral axis measured between the bend tangent lines (BTLs). Bend allowance 2023-11-16 B1-07d Maintenance Practices Page 113 of 335 CASA Part Part 66 - Training Materials Only  Neutral Axis in the Centre (NA) BA Approach One method of calculating BA assumes the neutral axis is in the centre of the metal. We can calculate the BA by finding the circumference of a circle (πD) drawn at the centre of the material (neutral axis). Calculate the distance from the centre of the BR to the neutral axis. This radius is equal to: BR + M T ÷ 2 Diameter = 2BR + M T ∴ Circumf erence = π(2BR + M T ) Calculating bend allowance The circumference is calculated using πD. This is the amount of metal required to form a full circle. 2023-11-16 B1-07d Maintenance Practices Page 114 of 335 CASA Part Part 66 - Training Materials Only  Calculating Bend Allowance The following values for bend radius and material thickness have been provided. Where BR = 0.250 in. and MT = 0.064 in. calculate the bend allowance using the NA approach. You may take π as 3.1416 for this exercise. C = π (2BR + M T ) = 3.1416 (2 × 0.250 in. + 0.064 in. ) = 3.1416 (0.500 in. + 0.064 in. ) = 3.1416 × 0.564 in. = 1.77186 in. This is the amount (length) of metal required to form a full circle. Bend allowance calculation Now that you know how much material is in a full (360°) circle, the next step is to determine how much metal is required in only the bend (in this case the bend is 90°). To work out this, the amount of material per one degree will be found and then it will be multiplied by the 90° bend. 2023-11-16 B1-07d Maintenance Practices Page 115 of 335 CASA Part Part 66 - Training Materials Only  Finding 1° of material length: 1° = Circumf erence ÷ 360 = 1.77186 in. ÷ 360 = 0.0049218 in. Multiplying it by 90 for the 90° bend: 90° = 0.0049218 in. × 90 7 = 0.44296 in. ⟹ in. 16 7 T heref ore, BA = in. 16 You may have noticed that you could have simply divided the 360° by 4 to get the 90° bend allowance. This process of finding the material per 1 degree works for all angles where the maths might not be as straightforward. The formulae for calculating bend allowance (BA), assuming that the neutral axis is in the middle of the material, is: 1 2π (BR + MT ) 2 BA = × Bend Angle 360 Calculating the BA by assuming the neutral axis is in the centre of the material is not the most accurate method, but it is close and works well for most cases. Bend allowance calculation 2023-11-16 B1-07d Maintenance Practices Page 116 of 335 CASA Part Part 66 - Training Materials Only  Empirical Formula (EF) BA Approach The most accurate method is using an empirical formula which places the neutral axis at 44.5% of the MT, measured from inside the bend. The formula to calculate the BA for 1° of bend is: BA = (0.0078 M T + 0.01743 BR) × Bend Angle Given the following bend radius, material thickness and bend angle, calculate the BA to three decimal places using the empirical formula. The BR = 0.250 inches, MT = 0.064 inches and the bend angle is 90°. BA = (0.0078 M T + 0.01743 BR) × Bend Angle BA = (0.0078 × 0.064 in. + 0.01743 × 0.250 in. ) × 90° = (0.0004992 + 0.0043575) × 90° 7 = 0.437 in. ⟹ in. 16 The empirical formula has been used to compile these tables: Bend allowance table 2023-11-16 B1-07d Maintenance Practices Page 117 of 335 CASA Part Part 66 - Training Materials Only  Bend Allowance Examples Calculate the BA for these three angles using both methods: Neutral Axis in the middle (NA approach) The Empirical Formulae (EF approach). Bend allowance calculations 2023-11-16 B1-07d Maintenance Practices Page 118 of 335 CASA Part Part 66 - Training Materials Only  Bend Allowance Answers 90° NA – 0.442944 in. (7/16 in.) EF – 0.437103 in. (7/16 in.) 45° NA – 0.221481 in. (7/32 in.) EF – 0.2185515 in. (7/32 in.) 135° NA – 0.66443 in. (43/64 in.) EF – 0.6556545 in. (43/64 in.) Note: The greater the bend angle, the greater the difference between the two formulae. Bend allowance answers 2023-11-16 B1-07d Maintenance Practices Page 119 of 335 CASA Part Part 66 - Training Materials Only  Flat Pattern Layout Following the calculations, the bend allowance and other dimensions need to be contextualised for a sheet of metal. The first question to ask is: What is it going to look like on a flat piece of metal? Flat pattern layout Step 1 - Using the values BR = 0.125° and MT = 0.032 inches (taken from the diagram below) the measurements for the flats and BAs need to be calculated and marked out on the sheet metal. This diagram does not explicitly provide the bend angle, however the straight lines illustrated allow the assumption that the angle is to be 90°. Note that the side length values (2.00 inches) will also be important. 2023-11-16 B1-07d Maintenance Practices Page 120 of 335 CASA Part Part 66 - Training Materials Only  Dimensions of the desired channel Step 2 – Calculate the setback and bend allowance. SB 90° = K (BR + M T ) 1 (0.125 in. + 0.032 in. ) 5 = 0.157 in. ⟹ in. 32 BA 90° = (0.0078 M T + 0.01743 BR) × 90° = (0.0078 × 0.032 in. + 0.0174×0.125 in. ) × 90° = 0.0024283 in. × 90° 7 = 0.218547 in. ⟹ in. 32 Once the setback and bend allowance are calculated, the length of the flats (the two sides and the base of the metal channel) can be calculated. Recall the flat calculation method. The side length measurement was provided in the original diagram, each side is to be 2.00 inches in length. Step 3 – Calculate length of flats (sides and base). 2023-11-16 B1-07d Maintenance Practices Page 121 of 335 CASA Part Part 66 - Training Materials Only  Sides = 2 in. − SB 90° = 2 in. − 0.157 in. 27 = 1.843 in. ⟹ 1 in. 32 Base = 2 in. − (2 SB 90°) = 2 in. − 0.314 21 = 1.686 in. ⟹ 1 in. 32 Calculating lengths of flats Step 4 - Now that all of the measurements have been found, the flat pattern should marked and the metal trimmed to size. 2023-11-16 B1-07d Maintenance Practices Page 122 of 335 CASA Part Part 66 - Training Materials Only  Mark flat pattern out and trim to size 2023-11-16 B1-07d Maintenance Practices Page 123 of 335 CASA Part Part 66 - Training Materials Only  Sight Line To have the bend starting on the bend tangent line (BTL), it is necessary to mark a sight line one radius length from the BTL because the BTL will be hidden beneath the radius block. This prevents the error that the radius block would cause if you used the BTL as your sight line. Using a sight line Step 5 - To complete the process from the previous section, the final step is to mark the sight lines and then form the channel. 2023-11-16 B1-07d Maintenance Practices Page 124 of 335 CASA Part Part 66 - Training Materials Only  Sight lines marked on the flat pattern layout 2023-11-16 B1-07d Maintenance Practices Page 125 of 335 CASA Part Part 66 - Training Materials Only  Folding a Box Thus far, the sheet metal has been bent into simple shapes (a channel). How does this approach scale to a slightly more complex build, such as a metal box? Step 1 – What will it look like on a piece of metal? The first step is to mark the expected flat pattern layout of a box. Flat pattern layout of a box 2023-11-16 B1-07d Maintenance Practices Page 126 of 335 CASA Part Part 66 - Training Materials Only  Metal Box Instructions The required box must be 4 inches square in size and the sides of the box must be 1 inch high. The material used to build the box is given as 2024-T3, 0.051 in. and the bend radius is 5/32 inches. Step 2 – Calculate SB and BA. SB 90° = K (BR + M T ) = 1 (0.15625 in. + 0.051 in. ) 13 = 0.207 in. ⟹ in. 64 BA 90° = (0.0078 M T + 0.01743 BR) × 90° = (0.0078 × 0.051 in. + 0.01743 × 0.15625 in. ) × 90° = (0.0003978 in. + 0.0027234 in. ) × 90° = 0.0031212 in. × 90° 9 = 0.280908 in. ⟹ in. 32 Calculating setback and bend allowance for the metal box 2023-11-16 B1-07d Maintenance Practices Page 127 of 335 CASA Part Part 66 - Training Materials Only  Calculating the lengths of flats Step 3 – Calculate length of flats. Because it is a square box: A = B. A & B = 4 in. − (2 SB) = 4 in. − 0.414 in. 19 = 3.586 in. ⟹ 3 in. 32 Because the sides are all 1 in. high: C = D = E = F C&D&E&F = 1 in. − 0.207 in. 51 = 0.793 in. ⟹ in. 64 2023-11-16 B1-07d Maintenance Practices Page 128 of 335 CASA Part Part 66 - Training Materials Only  Calculating the lengths of flats Step 4 – Once the pattern is drawn, consideration must be given to cutting or ‘notching’ waste material. Start by deciding which two sides are going to fit inside the other two. Cutting or notching waste material Side D and F are going to fit between sides C and E once bent. Sides C and E have cut lines marked 1SB from the BTL for length. Sides D and F have cut lines marked 1SB – 1MT from the BTL. 2023-11-16 B1-07d Maintenance Practices Page 129 of 335 CASA Part Part 66 - Training Materials Only  Therefore, the length of C and E should be same as the outside of box. D and F should be the length of the box minus 2MTs. Calculating the lengths of the folded sides Step 5 – Drill relief holes and notch out waste material. To prevent cracks emanating from the corners of the bends, relief holes are drilled. A good rule of thumb for the size and position of relief holes is Diameter = 2BR. The centre of a hole must be at the intersection of the inner BTLs. 2023-11-16 B1-07d Maintenance Practices Page 130 of 335 CASA Part Part 66 - Training Materials Only  Marking and drilling relief holes Step 6 – Determine the bending sequence and mark sight lines. Think about the bending sequence and how it will affect which BTLs your sight lines will be measured from. Remember: The BTL that goes under the folder is where the sight line must be measured from. Example 1 – If Side C is placed under the folder, then the sight line will be measured from this BTL. Example 2 – if the base is placed under the folder, then the sight line will be measured from this BTL. 2023-11-16 B1-07d Maintenance Practices Page 131 of 335 CASA Part Part 66 - Training Materials Only  Determining bending sequence and marking sight lines Step 7 – Form the component. The finished box 2023-11-16 B1-07d Maintenance Practices Page 132 of 335 CASA Part Part 66 - Training Materials Only