A&P Practical Sheet Metal Layout: Bends and Rivet Rows
A&P practical sheet metal layout practice starts with the assigned drawing and ends with dimensions you can check on the work. This O&P guide uses a fictional 90-degree bracket and a separate rivet-row exercise. The numbers are study illustrations, not a repair design for an aircraft.
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Which sheet-metal skills can the O&P evaluate?
The Airframe section of the ACS (AM.II.A, Metallic Structures) includes designing a repair using the manufacturer’s structural repair manual, making a repair drawing that identifies rivet quantity and sheet size, installing and removing solid rivets, and trimming and forming sheet to fit a prepared area. Those skills are broader than memorizing a bend-allowance answer.
On the test and on real aircraft, follow the manufacturer’s data or other applicable approved data; on the test, the DME explains the task you must perform. The study examples below do not establish aircraft-specific limits or replace the assigned procedure. The Airframe handbook points to manufacturer maintenance-manual charts for minimum bend radius and, for rivet spacing on most repairs, to the spacing the manufacturer used around the damage, adding that the aircraft’s SRM may also be consulted.
FAA-S-ACS-1, p. A-3 · FAA Order 8900.1, Vol. 5, Ch. 5, Sec. 11, p. 16 · FAA-H-8083-31B, p. 4-59 · FAA-H-8083-31B, p. 4-33
What are the givens for the bend illustration?
Assume an assigned training drawing specifies a single 90-degree bend, inside radius R = 0.250 in, thickness T = 0.040 in, and outside mold-line dimensions of 1.000 in and 2.000 in. Treat those values as fictional drawing inputs, not as proof that the radius suits an unspecified alloy and temper.
Use one calculation method consistently. The handbook gives SB = K(R+T), with K = 1 for a 90-degree bend, and Flat = MLD - SB. For this illustration we use its Formula 2 for bend allowance: BA = (0.01743R + 0.0078T)N, where N is the number of degrees of bend. This method uses the handbook’s stated constants rather than mixing in the bend allowance from another method.
FAA-H-8083-31B, p. 4-63 · FAA-H-8083-31B, p. 4-64
| Step | Illustrative arithmetic | Result |
|---|---|---|
| Setback | 1 × (0.250 + 0.040) | 0.290 in |
| First flat | 1.000 - 0.290 | 0.710 in |
| Second flat | 2.000 - 0.290 | 1.710 in |
| Bend allowance | (0.01743 × 0.250 + 0.0078 × 0.040) × 90 | 0.420255 in |
| Developed width | 0.710 + 1.710 + 0.420255 | 2.840255 in |
FAA-H-8083-31B, p. 4-63 · FAA-H-8083-31B, p. 4-64
For the drawing in this exercise, the calculated blank width is approximately 2.8403 in. Retain the unrounded values until the last step. Use the assigned drawing’s tolerances to decide how to mark and inspect the real work; this four-decimal display is not an FAA tolerance.
How do you lay out a rivet row?
The handbook’s straight-row procedure starts by locating the edge distance at each end and then laying off the rivet pitch. The handbook also says that, beyond matching the manufacturer’s original spacing, no specific set of rules governs rivet spacing in all cases, although certain minimum requirements must be observed. Work from the assigned drawing and applicable SRM rather than treating one memorized multiplier as every repair’s limit.
FAA-H-8083-31B, p. 4-34 · FAA-H-8083-31B, p. 4-33
For a separate fictional row, let the drawing give a 4.375-in length, 0.125-in rivet diameter, 0.3125-in end distances, and 0.750-in pitch. The end distance is 2.5D and the pitch is 6D in this illustration; these are chosen exercise inputs, not universal minima.
| Check | Illustrative calculation | Result |
|---|---|---|
| Distance between first and last centers | 4.375 - 2 × 0.3125 | 3.750 in |
| Number of spaces | 3.750 ÷ 0.750 | 5 |
| Number of rivet centers | 5 + 1 | 6 |
| Centers from the left edge | 0.3125; 1.0625; 1.8125; 2.5625; 3.3125; 4.0625 | 0.750-in intervals |
The handbook’s spacing guidance is not identical throughout: page 4-33 gives 3½D as the minimum spacing between protruding-head rivets but also says pitch should be at least 3D when new sections are added, and page 4-34 gives 3D for one- and three-row layouts and 4D for a two-row layout. Do not resolve those differences by applying the smaller value to a repair. Use the aircraft-specific data or the drawing you are given; on the test, the DME explains the task, and locating and applying the right reference data is part of what you demonstrate. The fictional 6D pitch above is an exercise value, not a decision between those statements.
FAA-S-ACS-1, p. A-1 · FAA Order 8900.1, Vol. 5, Ch. 5, Sec. 11, p. 16 · FAA-H-8083-31B, p. 4-33 · FAA-H-8083-31B, p. 4-34
What should you inspect before forming or drilling?
Our suggested study check is to label the drawing inputs, the chosen bend method, each flat, and the hole centers before making the part. Recheck the end distances and the first-to-last center span. Then follow the assigned procedure for forming, drilling, and inspecting the work. For terminology review, use the separate sheet-metal oral guide.
Frequently asked questions
Will every O&P sheet-metal project use this bracket?
No. This bracket is an invented exercise; the ACS includes several metallic-structure skills, and you are not permitted to know before testing which selections will be on your test.
FAA-S-ACS-1, p. 19 · FAA-S-ACS-1, p. A-1
Are setback and bend allowance the same number in this example?
No. The illustrated setback is 0.290 in and the bend allowance is 0.420255 in, calculated with the two different handbook formulas shown in the worked steps.
FAA-H-8083-31B, p. 4-63 · FAA-H-8083-31B, p. 4-64
Can I treat 3D as the universal minimum rivet pitch?
No. The handbook gives different minimum spacing figures by context, such as 3½D between protruding-head rivets and 3D for one- and three-row layouts; the assigned drawing and the applicable aircraft data settle the layout, not a memorized multiplier.
FAA-H-8083-31B, p. 4-33 · FAA-H-8083-31B, p. 4-34
Why are there six centers but only five spaces?
Because the example’s five equal intervals connect a first center to a last center; counting both endpoints gives six rivets. This is the geometry of the invented row, not a rivet-count rule for repairs.
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Related guides
Sources
FAA sources checked October 18, 2026.
- FAA-S-ACS-1
- FAA Order 8900.1, Vol. 5, Ch. 5, Sec. 11, Administer an Oral and a Practical Test (CHG 929, 9/17/2024)
- FAA-H-8083-31B, Aviation Maintenance Technician Handbook—Airframe
About this guide: drafted with AI from the FAA sources listed on this page and checked claim by claim against them. Not reviewed by an A&P mechanic or DME. How we make our guides
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