Architectural Flashing Supply
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Tier 2 · Fabrication Technician

Flat patterns and bend allowances

The geometry of a bend and the numbers that turn a drawn profile into a flat blank: bend allowance, setback, bend deduction and the K-factor. Worked AFS order blanks and developed blanks, K calibrated from test pieces, and how to diagnose parts that come out long or short.

4 lessons · about 41 min · 12 diagrams · 5 videos

Version 1.1.0

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Lessons

0 of 4 complete

  1. Lesson 1 · 11 min · 12 slides · 8 questions

    Flat patterns and bend allowances: principles and terminology

    The geometry of one bend: mold line, tangent lines, inside radius, neutral axis and K, and the three numbers that turn a drawn profile into a flat blank.

    You will be able to: Name the parts of a bend, define bend allowance, setback, bend deduction and the K-factor, tell the AFS order blank from a developed blank, and state the safety limits.

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  2. Lesson 2 · 9 min · 12 slides · 7 questions

    Flat patterns and bend allowances: materials, standards and design constraints

    What K and the inside radius depend on, published values and their limits, painted coil and the 2T rule, gauge tolerance, press brake versus folder, and the limits a blank must fit.

    You will be able to: Explain what sets K and the inside radius, read published values as typical rather than AFS values, allow for thickness tolerance and coating limits, and check a blank against AFS limits.

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  3. Lesson 3 · 12 min · 12 slides · 9 questions

    Flat patterns and bend allowances: methods and worked application

    Three methods with worked numbers: the AFS order blank, the developed blank with hems and a reverse bend, and K from test pieces, then how the drawing reaches the folder.

    You will be able to: Work out the AFS order blank and a developed blank for a hemmed profile, calibrate K from test pieces, and record every assumption and unit.

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  4. Lesson 4 · 9 min · 11 slides · 7 questions

    Flat patterns and bend allowances: defects, verification and case study

    The flat-pattern errors that make formed parts long or short, how each shows, the checks on a formed part, and a worked case from order to record.

    You will be able to: Diagnose a formed part that is long or short from a flat-pattern error, choose the correction, and document the evidence for review.

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Practical task

Produce a flat-pattern job packet for a hemmed L-flashing or a FlashDraft profile in 24 ga galvanized: the AFS order blank, a developed blank from your own test pieces or the stated example values, and the checks on the formed part.

Hand in

  • A decision rationale: which blank model is used for what, and why
  • A marked-up sketch: mold-line legs, turn angles and directions, hems and their side, and the face the legs are measured on
  • An assumptions table: t and its source, R and K and their source, angle convention, units and rounding
  • A calculation sheet: BA, setback and BD at every bend, the developed hems with the hem measuring convention stated, the order blank and the developed blank
  • A test-piece log of at least three pieces if K was calibrated: measured legs, radius, worked K and the average
  • A quality checklist for the formed part and a defect analysis of one deviation: cause, correction and evidence

Rubric

CriterionMeets the standard when
SourcesEvery number names where it came from: the register, a cited source, a measurement, or an example value labelled as such.
Model choiceThe order blank and the developed blank are kept apart and each is used for its own job.
CalculationBA uses the turn angle in radians; setbacks are outside or inside as the measured face requires; the arithmetic checks.
AssumptionsThickness, R, K, angle convention, measured face, hem measuring convention and units are written down before the numbers.
VerificationLegs are measured to the mold line, angles and radius recorded, hems and coating checked, thickness within the gauge range.
Defect analysisThe deviation is traced to a flat-pattern cause with numbers, and the correction is stated and recorded.
SafetyThe packet notes hand protection for cut edges and that no machine was run outside a trained, guarded set-up.

Module quiz

10 questions drawn from a bank of 31; a new set each attempt. Pass mark 80%.

1. How does the FAA handbook define the mold line?
2. What is the largest K-factor seen in practice, according to The Fabricator?
3. At 24 ga, how far does a 0.001 in reading error in the legs move K?
4. In the 90 deg worked example, how much does the bend deduct?
5. What does The Fabricator say never to use when calculating bend allowance?
6. In the case study, how short in girth does the part come out?
7. On the Profile tool's hem convention, with the example R and K, what is the developed blank of the hemmed L-flashing?
8. What sets the minimum bend radius?
9. In the example, how much too wide is the blank when the included angle is used?
10. If the leg and the foldback are both measured to the outside of the fold, what is the developed blank?