Advanced geometric pattern development · Lesson 2 of 4

Advanced geometric pattern development: materials, standards and design constraints

Which documents govern a pattern, the allowances added outside a development and how to calculate them, where seams go, and how sheet size, thickness, AFS's limits and the number of divisions constrain a pattern.

You will be able to: Identify who sets the rules for a pattern on a job, add seam and edge allowances to a development, place seams, and check a pattern against sheet size, thickness and AFS's published limits.

10 min · 10 slides · 7 questions

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Slide 1 of 10

Who sets the rules for a pattern

The Red Seal standard (Canada) describes trade competency; the US Navy manuals (1994, 1996) are training texts. Neither is a building code.

On a job, the project specification and the system manufacturer's instructions govern the pattern's seams, edges and allowances.

SMACNA publishes the Architectural Sheet Metal Manual (7th edition, 2012) for architectural sheet metal work.

Sources

Red Seal Occupational Standard, Sheet Metal Worker (2026), Task B-6 Performs pattern development - Employment and Social Development Canada (Red Seal Program)
Blueprint Reading and Sketching, NAVEDTRA 14040 (May 1994), Chapter 8 Developments and Intersections - U.S. Navy, Naval Education and Training Professional Development and Technology Center
Architectural Sheet Metal Manual, 7th edition (2012) - SMACNA (listing on the ICC store)

Glossary

Grooved seam: A locked seam joining two edges; in the US Navy Steelworker manual its allowance is three times the lock width, half added to each edge.
Blank width: FlashDraft's flat width of a folded profile: the legs measured to the mold line plus hem allowances. It ignores bend radius, so it is informational.
Hem allowance (FlashDraft): The extra flat width FlashDraft adds for a hem when it quotes a profile: a quoting simplification, not a fabrication bend-deduction calculation.
Seam placement: Where the seam of a development is put: normally on the shortest side, with the seams of an elbow's pieces placed alternately 180 deg apart to avoid waste.