Chapter 2C - Sheet Metal Fabrication
On a properly driven rivet, the width of the bucked head must be ______ times the original shank diameter and the height must be _______ times the original shank diameter.
1.5; 0.5
Adjacent rivets in a row should be no closer than _______ diameters, and no further apart than ________ to _______ diameters of the rivet shank.
3; 10; 12
The distance between rows of staggered rivets should be _______ % of the distance between rivers in a given row.
75%
2C-27 D07A Unless otherwise specified, the radius of a bend is the A — radius of the neutral axis plus one half the thickness of the metal being formed. B — inside radius of the metal being formed. C — inside radius plus one half the thickness of the metal being formed.
Answer B. JSAT 2-70 (AC65-15A) The radius of a bend on a sheet of material is the distance from the intersection of the bend tangent lines to the inside of the bend, or it is the radius measured on the inside curve of the material.
2C-1 D01A A well designed rivet joint will subject the rivets to A — compressive loads. B — tension loads. C — shear loads
Answer C. JSAT 2-51 (AC65-15A) Rivets hold pieces of aircraft skin together, and in a properly designed riveted joint, the rivets support shear loads only.
What are the two special calculations that must be made when bending sheet metal?
Answer — Bend allowance and setback. JSAT 2-71
What are the two reasons for installing a lightening hole in a sheet metal wing rib?
Answer — Lightening holes reduce the weight and increase stiffness. JSAT 2-81
What is done to a corner where two bends intersect to prevent cracking?
Answer — Relief holes are drilled in the corner. JSAT 2-77
What factors must be considered in order to determine setback?
Answer — The thickness of the metal and the bend radius. JSAT 2-71
The head angle of an MS20426 rivet is ________ degrees.
100
For a rivet joint to develop its required strength, no rivet should be installed with its center nearer to the edge of a sheet than ______ rivet diameters.
2
In order for sheet metal pieces to be flat against the skin and yet have one flat on top of another, a process called ___________ is used.
joggling
An AN470DD6 rivet would be most properly driven with a(n) _______________ rivet gun.
one-shot
2C-18 D06A A sheet metal repair is to be made using two pieces of 0.0625-inch aluminum riveted together. All rivet holes are drilled for 1/8 inch rivets. The length of the rivets to be used will be A — 5/16 inch. B — 3/16 inch. C — 5/32 inch.
Answer A. JSAT 2-52 (AC43.13-1 B) To find the rivet shank length, add the material thickness and then add 1-1/2 times the rivet diameter. The material required to form the shop head is .3125" or 5/16" total shank length.
2C-3 D01A The shop head of a rivet should be A — one and one-half times the diameter of the rivet shank. B — one and one-half times the diameter of the manufactured head of the rivet. C — one-half times the diameter of the rivet shank.
Answer A. JSAT 2-53 A properly formed shop head is one-half the shank diameter high, its diameter is one-and-one-half times that of the shank, and it is concentric with the hole.
The formula used to determine setback of an angle other than 90 degrees is:
Setback = (BR + MT)k
For a bend of 90 degrees, the setback is calculated using what formula?
Setback = BR + MT Where: BR = Bend Radius MT = Material Thickness
What is done to lightening holes in a wing rib to add stiffness?
They may be flanged
The amount of material actually involved in the bend is known as the
bend allowance
When installing rivets according to the N.A.C.A. method, the manufactured head is placed on the ______________ of the structure.
inside
For a bend of more or less than 90 degrees, we must apply a correction factor known as a(n) _______ -factor to find the setback.
k
Indicate the minimum bend radius of each of these types of metal by referring to the bend radius chart in figure 2-127 of the "Jeppesen A&P Technician Airframe Textbook" > 0.032-inch 5052-O: _______ inch > 0.032-inch 2024-T3: _______ inch > 0.064-inch 7075-T6: _______ inch
> 0.032-inch 5052-O: 0 inch > 0.032-inch 2024-T3: 2t-4t inch > 0.064-inch 7075-T6: 4t-6t inch
What size drill should be used for the installation of each of these rivet sizes: > 3/32-inch: __________ > 1/8-inch: __________ > 5/32-inch: __________ > 3/16-inch: __________
> 3/32-inch: #40 > 1/8-inch: #30 > 5/32-inch: #21 > 3/16-inch: #11
The tapping code used in team riveting is: > Bad rivet: ________ taps > Good rivet: ________ taps > Drive the rivet some more: _______ taps
> Bad rivet: 3 taps > Good rivet: 2 taps > Drive the rivet some more: 1 tap
2C-10 D05A A factor which determines the minimum space between rivets is the A — diameter of the rivets being used. B — length of the rivets being used. C — thickness of the material being riveted.
Answer A. JSAT 2-54 (AC65-15A) Rivet spacing, known as pitch, is determined by the diameter of the rivets being used.
2C-14 D06A Which of the following need not be considered when determining minimum rivet spacing? A — Rivet length. B — Type of material being riveted. C — Rivet diameter.
Answer A. JSAT 2-54 (AC65-15A) The length of the rivet has no effect on the rivet spacing.
2C-20 D06A What is generally the best procedure to use when removing a solid shank rivet? A — Drill to the base of the manufactured rivet head with a drill one size smaller than the rivet shank and remove the rivet with a punch. B — Drill through the manufactured head and shank with a drill one size smaller than the rivet and remove the rivet with a punch. C — Drill through the manufactured head and shank with a shank size drill and remove the rivet with a punch.
Answer A. JSAT 2-67 Using a drill one size smaller than the shank of the rivet, and drilling only through the head should prevent enlarging the rivet hole.
2C-19 D06A The length of a rivet to be used to join a sheet of .032 inch and .064 inch aluminum alloy should be equal to A — one and one half times the rivet diameter plus .096 inch. B — three times the rivet diameter plus .096 inch. C — two times the rivet diameter plus .064 inch.
Answer A. JSAT 2-52 (AC65-15A) When determining total rivet length, the combined thickness of the materials to be joined must be known. This measurement is grip length. The total length of the rivet must be grip length plus 1-1/2 times the diameter of the rivet shank (necessary to form a shop head on the rivet).
2C-2 D01A The general rule for finding the proper rivet diameter is
Answer A. JSAT 2-52 (AC65-15A) As a general rule, the rivet diameter should be not less than three times the thickness of the thickest sheet being riveted.
When practical, bends should be made _________ the grain of the metal.
across
What type of dimpling is used on magnesium sheets to prevent them from cracking in the dimpling process?
hot dimpling
2C-15 D06A A rivet set used to drive MS20470 rivets should A — be nearly flat on the end, with a slight radius on the edge to prevent damage to the sheet being riveted. B — have a slightly greater radius than the rivet head. C — have the same radius as the rivet head.
Answer B. JSAT 2-64 The radius of the cup of the rivet set must be slightly larger than the radius of the rivet head. If it is too small, it will produce a small indentation on the head of the rivet. If it is too large, it will produce the same indentation on the skin around the rivet.
2C-24 D07A When a piece of aluminum alloy is to be bent using a minimum radius for the type and thickness of material, A — less pressure than usual should be applied with the movable (upper) clamping bar. B — the layout should be made so that the bend will be 90 degrees to the grain of the sheet. C — the piece should be bent slowly to eliminate cracking.
Answer B. JSAT 2-69 (AC65-15A) The sheet metal we use for aircraft construction and repair was formed from an ingot of aluminum alloy passed through a series of rollers until it was reduced to the thickness needed. In the process of rolling, the metal assumes a grain structure which is easy to see in a piece of sheet aluminum alloy. When laying out a pattern, the bends in the metal should be made across the grain as much as possible.
2C-37 D07A (Refer to Airframe figure 5) What is the length of flat A? A — 3.9 inches. B — 3.7 inches. C — 3.8 inches.
Answer B. JSAT 2-70 (AC65-15A) Using the setback formula given in the drawing, substitute .25 for R and .062 for T. Performing the calculation you get .312. To find the flat, subtract the setback from the mold line dimension. Therefore, 4 - .312 = 3.688. Rounding 3.688 to one decimal accuracy we get 3.7.
2C-21 D06A The length of rivet to be chosen when making a structural repair that involves the joining of 0.032 inch and 0.064 inch aluminum sheet, drilled with a No. 30 drill, is A — 1/4 inch B — 7/16 inch C — 5/16 inch
Answer C. JSAT 2-52 The length of rivet to use is determined by adding together the thickness of the material, and then adding 1-1/2 times the diameter of the rivets to this value. The thickness of the material in this case is .096". A No. 30 drill is .1285" diameter, which would take a 1/8" diameter rivet. One and one-half times the rivet diameter, or 3/16", plus the thickness of the material, would call for a rivet 5/16" in length.
2C-17 D06A Which rivets should be selected to join two sheets of .032-inch aluminum? A — MS20455DD-5-3. B — MS20425D-4-3. C — MS20470AD-4-4.
Answer C. JSAT 2-52 (AC65-15A) To join the two pieces of aluminum together, the rivet will need to be .064" long plus 1-1/2 times its diameter. The AN470AD-4-4 rivet is 1/8" in diameter and 1/4" long. This rivet meets the length requirement.
2C-6 D05A What is the minimum edge distance for aircraft rivets? A — Three times the diameter of the rivet shank. B — Two times the diameter of the rivet head. C — Two times the diameter of the rivet shank.
Answer C. JSAT 2-53 (AC65-15A) If rivets are too close to the edge, the sheet is likely to tear, but if they are too far back, the edge of the sheet will lift. Accepted practice is to have an edge distance of no less than two times the diameter of the rivet.
2C-9 D05A Aircraft structural units, such as spars, engine supports, etc., which have been built up from sheet metal, are normally A — repairable, using approved methods. B — not repairable, but must be replaced when damaged or deteriorated. C — repairable, except when subjected to compressive loads.
Answer A. JSAT 2-51 (AC43.13-1B) Aircraft structural units, which are made from sheet metal, are generally repairable if the repair procedures used bring the aircraft back to an airworthy condition, and meet the requirements of the Federal Aviation Administration.
2C-12 D05A Rivet pitch is the distance between the A — centers of adjacent rivets in the same row. B — heads of rivets in the same row. C — centers of rivets in adjacent rows.
Answer A. JSAT 2-54 The distance between adjacent rivets in a row is called the pitch of the rivet.
2C-23 D07A A piece of flat stock that is to be bent to a closed angle of 15 degrees must be bent through an angle of A—165 degrees. B — 105 degrees C — 90 degrees .
Answer A. JSAT 2-71 (AC65-15A) When a closed angle is referred to, it means an angle that is formed by taking a flat piece of stock and bending it past 90 degrees, to where the two ends of the stock start coming together. Because there are 180 degrees in a piece of flat stock, to end up with a closed angle of 15 degrees would require a bend of 165 degrees.
When three sheets of metal are dimpled and stacked to be riveted together, they should be _____________ dimpled.
coin
If a piece of metal becomes too hard when it is being bumped into a compound curve, it _________ be annealed to soften it.
may
The point of intersection of the mold lines of two sides of a bend is called the __________ point.
mold
The distance from the mold point to the bend tangent line is known as the ___________.
setback
When bending a bulb angle into a curve, the flange of the metal with the bulb must be ____________.
stretched
2C-26 D07A If it is necessary to compute a bend allowance problem and bend allowance tables are not available, the neutral axis of the bend can be A — found by adding approximately one half of the stock thickness to the bend radius. B — represented by the actual length of the required material for the bend. C — found by subtracting the stock thickness from the bend radius.
Answer A. JSAT 2-70 (AC65-15A) The line along which the portion of sheet being bent does not shrink or stretch is called the neutral axis of the metal. It is not located exactly in the center of the sheet, but is actually about 44.5% of the sheet thickness from the inside of the bend. For practical purposes, we can consider this to be in the center.
2C-28 D07A The sharpest bend that can be placed in a piece of metal without critically weakening the part is called the A — minimum radius of bend. B — bend allowance. C — maximum radius of bend.
Answer A. JSAT 2-70 (AC65-15A) The radius of bend of a sheet of material is the radius of the bend as measured on the inside of the curved material. The minimum radius of bend of a sheet of material is the sharpest curve, or bend, to which the sheet can be bent without critically weakening the metal at the bend.
2C-30 D07A A piece of sheet metal is bent to a certain radius. The curvature of the bend is referred to as the A — bend radius. B — bend allowance. C — neutral line.
Answer A. JSAT 2-70 (AC65-15A) The bend radius for a piece of sheet metal is the distance from the intersection of the bend tangent lines to the inside of the bend or it is the measure of the inside curve of the bend.
2C.22 D07A If a streamline cover plate is to be hand formed using a form block, a piece of dead soft aluminum should first be placed over the hollow portion of the mold and securely fastened in place. The bumping operation should be A — started by tapping the aluminum lightly around the edges and gradually working down into the center. B — distributed evenly over the face of the aluminum at all times rather than being started at the edges or center. C — started by tapping the aluminum in the center until it touches the bottom of the mold and then working out in all directions.
Answer A. JSAT 2-80 (AC65-15A) With a bumping block clamped in a bench vise, a soft-faced mallet or hard-wood drive block and suitable mallet should be used to start the bumping action. With light blows of the mallet, work the material down gradually from the edges. The object of the bumping process is to work the material into shape by stretching it, rather than by forcing it into the form with heavy blows. Always start bumping near the edge of the form; never start near the center of the blister.
2C-16 D06A A sheet metal repair is to be made using two pieces of 0.040-inch aluminum riveted together. All rivet holes are drilled for 3/32 inch rivets. The length of the rivets to be used will be A — 5/16 inch. B — 1/4 inch. C — 1/8 inch.
Answer B. JSAT 2-52 (AC43.13-1 B) To properly form a rivet shop head, the rivet length (L) should be equal to the thickness of the metal being joined (grip) plus one and one-half times the diameter (D) of the rivet or (L = Grip + 1.5 x D). Substituting the values from the question into the formula we get L = (.040 + .040) + 1.5 x 3/32 or approximately .221". Standard rivet lengths are in increments of 1/32", and the closest standard length is .25" or 1/4".
2C-5 D05A A single lap sheet splice is to be used to repair a section of damaged aluminum skin. If a double row of 1/8-inch rivets is used, the minimum allowable overlap will be A — 3/4 inch. B — 13/16 inch. C— 1/2 inch.
Answer B. JSAT 2-53 (AC65-15A) The minimum edge distance when riveting is two times the diameter of the rivet, which in this case is 1/4". Because this is an overlap splice, there are two edge distances involved, or a total of 1/2". The minimum pitch, or distance between rivets, should be no less than three times the diameter. The transverse pitch, or distance between rows, should be about 75% of the pitch. In this case, 75% of 3/8" is 9/32". The edge distance total of 1/2", and the transverse pitch of 9/32", gives a total of 25/32" minimum overlap. The only answer that gives at least this overlap is 13/16 inch.
2C-11 D05A Rivet gauge, or transverse pitch is the distance between the A — heads of rivets in the same row. B — centers of rivets in adjacent rows. C — centers of adjacent rivets in the same row.
Answer B. JSAT 2-54 The distance between the rows of rivets in a multi-row layout should be about 75% of the pitch, and the rivets in adjacent rows should be staggered.
2C-7 D05A What is the minimum spacing for a single row of aircraft rivets? A — Three times the length of the rivet shank. B — Three times the diameter of the rivet shank. C — Two times the diameter of the rivet shank.
Answer B. JSAT 2-54 (AC65-15A) The minimum spacing, or pitch, for a single row of rivets is three times the diameter of the rivet shank.
2C-4 D05A How many MS20470 AD-4-6 rivets will be required to attach a 10 x 5 inch plate, using a sin single row of rivets, minimum edge distance, and 4D spacing? A — 54. B — 56. C — 52.
Answer B. JSAT 2-55 (AC43.13-1B) | The rivets identified in this question are 4/32" in diameter. Minimum edge distance, according to the AC43.13-1B, is two times the diameter. This gives an edge distance of 1/4 inch. One-fourth of an inch taken away from each side of the plate leaves the dimensions as 4-1/2" by 9-1/2". With four times the rivet diameter spacing, the spacing will be 1/2 inch. Because the plate has two 4-1/2" sides and two 9-1/2" sides (in terms of rivet installation), there are 28 inches total to be covered, with ½" spacing, or 56 rivets needed.
2C-8 DOSA What is one of the determining factors which permits machine countersinking when flush riveting? A — Thickness of the material and rivet diameter are the same. B — Thickness of the material is greater than the thickness of the rivet head. C — Thickness of the material is less than the thickness of the rivet head.
Answer B. JSAT 2-58 (AC65-15A) As a general rule, use the drill or machine countersink method when the thickness of the material is greater than the thickness of the rivet head. If the material is too thin, drill or machine countersinking will grind away too much of the material. In this case, dimpling should be used.
2C-13 D05A (Refer to Airframe figure 2) Select the preferred drawing for proper countersinking. A — 2. B — 1. C — All are acceptable.
Answer B. JSAT 2-60 (AC65-15A) In order to insure that a countersunk rivet has sufficient bearing strength, the thickness of the sheet that is to be countersunk must be at least as thick as the depth of the rivet head (#2 in figure 2). However, it is preferable to have the skin thicker than the depth of the rivet head (#1 in figure 2).
When repairing an all-metal aircraft, how do you determine what metals should be used?
Answer — Always use metal of the same type and thickness as the original structure. JSAT 2-86
2C-25 D07A The flat layout or blank length of a piece of metal from which a simple L shaped bracket 3 inches by 1 inch is to be bent depends upon the radius of the desired bend. The bracket which will require the greatest amount of material is one which has a bend radius of A — 1/2 inch. B — 1/4 inch. C — 1/8 inch.
Answer C. JSAT 2-69 (AC65-15A) The smaller the bend radius in an L-shaped bracket, the greater the amount of material needed to make the bracket. If the bracket is made from 1/8" sheet metal, with a bend radius of 1/8", the flat layout would need to be 3.742" long. As the bend radius becomes greater, the length of the flat layout becomes less.
2C-29 D07A The most important factors needed to make a flat pattern layout are A — radius, thickness. and mold line. B — the lengths of the legs (flat sections). C — radius, thickness, and degree of bend.
Answer C. JSAT 2-70 (AC65-15A) In order to make a flat pattern layout, the technician must know the radius of the bend, because this must be accounted for when calculating bend allowance. The thickness of the material is needed so the technician can calculate the setback, and thickness is also accounted for in calculating bend allowance. The degree of bend is also needed when calculating bend allowance.
2C-41 D07A (Refer to Airframe figure 7) What is dimension F? Setback at D = .095; Setback at E = .068; Bend allowance at D = .150; Bend allowance at E = . 112 A —4.836 B — 5.738 C— 5.936
Answer C. JSAT 2-70 (AC65-15A) The dimension "F" is the total flat layout for the object. This dimension is going to equal the individual flats "A", plus "B", plus "C", plus the bend allowances at "D" and "E". Keeping in mind that the dimension of a flat is equal to the mold line minus the setback, the following dimensions can be calculated: Flat "A" = 1 - .095 or .905; Flat "B" = 3 - .095 and .068 or 2.837; Flat "C" = 2 - .068 or 1.932; Bend Allowance at "D" = .150 Bend Allowance at "E"= . 112. The total of the five dimensions above is 5.936.
2C-38 D07A (Refer to Airframe figure 5) What is the flat layout dimension? A — 6.6 inches. B — 7.0 inches. C — 6.8 inches.
Answer C. JSAT 2-70 (AC65-15A) The flat layout for a 90 degree bend should be accomplished by the following steps. First calculate the setback using the formula given (.312). Then subtract the setback from the given mold line dimensions. Flat A 4 - .312 = (3.688), Fiat B 3 - .312= (2.688). Then calculate the bend allowance using the formula given (.441). Calculate the sum of the flats and bend allowance to find the flat layout dimension. (3.688 + .441 + 2.688) 6.817 or 6.8
2C-32 D07A When bending metal, the material on the outside of the curve stretches while the material on the inside of the curve compresses. That part of the material which is not affected by either stress is the A — mold line. B — bend tangent line. C — neutral line.
Answer C. JSAT 2-70 (AC65-15A) Bending a strip compresses the material on the inside of the curve and stretches the material on the outside of the curve. However, at some distance between these two extremes lies a space which is not affected by either force. This is known as the neutral line or neutral axis.
2C-40 D07A (Refer to Airframe figure 6) What is dimension D? Setback = .252; Bend allowance = .345 A— 3.841 B— 3.492 C— 4.182
Answer C. JSAT 2-70 (AC65-15A) Dimension "D" in this figure is the total flat layout dimension. This dimension would be equal to the three flats "A", "B", and "C", plus two bend allowances for the two bends. The values for the three flats was calculated earlier, and the bend allowance is given in the question as .345. The three flats plus two of the bend allowances would give a total dimension of 4.182.
2C-39 D07A (Refer to Airframe figure 6) Determine the dimensions of A, B, and C in the flat layout. Setback = 252; Bend allowance = .345; A — A = 1.252; B = 2.504; C = 1.752 B — A = .748; B = 2.252; C = 2.004 C — A = .748; B = 1.496; C = 1.248
Answer C. JSAT 2-70 (AC65-15A) The dimension for flat "A" is its mold line of 1 minus the setback. The setback is given in this question as .252, so the dimension of flat "A" is .748. The dimension for flat "B" is its mold line of 2 minus two setbacks (one at each end), or 1.496. The dimension of flat "C" is its mold line of 1.5 minus the setback, or 1.248.
2C-35 D07A (Refer to Airframe figure 4) The length of flat A is A — 3.875 inches. B — 3.937 inches. C — 3.750 inches.
Answer C. JSAT 2-71 (AC65-15A) The length of flat "A" is equal to the total length from the mold point to the end of the flat, or 4", minus the setback. The setback for a 90 degree bend is equal to the metal thickness plus the radius of the bend. The thickness of the metal, .0625" or 1/1 6", plus the bend radius of 3/16", is equal to 1/4". Four inches minus 1/4" leaves a flat of 3.75".
2C-34 D07A On a sheet metal fitting layout with a single bend, allow for stretching by A — adding the setback to each leg. B — subtracting the setback from one leg. C — subtracting the setback from both legs.
Answer C. JSAT 2-71 (AC65-15A) When accounting for the total flat layout dimension when the object has a single bend, the two flats forming the bend must both have the setback subtracted from their mold line dimension, and then the bend allowance is added in.
2C-36 D07A (Refer to Airframe figure 4) The amount of material required to make the 90 degree bend is A — 0.3717 inch. B — 0.3925 inch. C — 0.3436 inch.
Answer C. JSAT 2-73 (AC65-15A) The amount of material required to make the bend is known as the bend allowance. The bend allowance for a 90 degree may be calculated using the formula given in the drawing. Simply substitute 3.14 for π, .1875 for R, and .0625 for T. Then complete the calculations.
2C-33 D07A The sight line on a sheet metal flat layout to be bent in a cornice or box brake is measured and marked A — one radius from either bend tangent line. B — one-half radius from either bend tangent line. C — one radius from the bend tangent line that is placed under the brake.
Answer C. JSAT 2-75 The sight line is a line that is made on a piece of metal to indicate where the metal is to be placed in a brake (the sight line is placed directly under the nose of the radius rod). To allow for the stretch of the metal it is placed one radius away from the bend tangent line that is placed under the brake shoe.
2C-31 D07A The purpose of a joggle is to A — decrease the weight of the part and still retain the necessary strength. B — increase obstruction for a sheet or an extrusion. C — allow clearance for a sheet or an extrusion.
Answer C. JSAT 2-82 (AC65-15A) A joggle is an offset formed on an angle strip to allow clearance for a sheet or an extrusion.
Describe a joggle and explain its function.
Answer — A joggle is an offset formed at an intersection of two or more sheets of metal to allow the multiple sheets to be stacked flat against each other. JSAT 2-82
