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Compound transitions and complex forms · Lesson 4 of 4

Compound transitions and complex forms: defects, verification and case study

The faults that ruin complex pieces, worked through with numbers: slant height versus height, true versus plan length, seam allowance, joints and laps; how to verify a pattern and inspect the work; and a chimney and pipe collar case study.

You will be able to: Diagnose a short cone, a transition that will not reach, a wrong joint or a missing cricket from its cause, choose a correction, and record the evidence a reviewer needs.

10 min · 10 slides · 6 questions

All lessons in this module
Slide 1 of 10

Four faults that ruin a complex piece

Four faults this module has met, each from a wrong length or a wrong lap:

  • The vertical height used where the slant height belongs.
  • Plan lengths used where true lengths belong.
  • Seam allowance counted inside the divisions.
  • A flat seam lapped against the flow.
Four faults, right and wrongFour pairs, right with a tick on the left, wrong with a cross on the right. 1: a frustum laid out from its slant height stands 10 in high; from its vertical height it stands 9.17 in high, 0.83 in short. 2: an element line at its 7.644 in true length reaches the round; at its 4.736 in plan length it falls short. 3: seam allowance added outside six equal parts, against an allowance squeezed inside the parts. 4: a flat seam with the upper sheet over the lower, against a lower sheet lapped over the upper so water runs into the lap.1Pattern radius2Element line length3Seam allowance4Flat seam lap10 in9.17 inhigh,0.83 inshort7.644 in4.736 infalls short6 equal partsseamseam inside partsupper over lowerwater into the lap

Four pairs, correct with a tick on the left, wrong with a cross on the right. 1 a frustum laid out with its slant height stands 10 in high; with its vertical height it stands 9.17 in. 2 an element line at its true length 7.644 in reaches the round; at its plan length 4.736 in it falls short. 3 seam allowance outside the divisions, versus counted inside them with the last division squeezed. 4 a flat seam with the upper sheet over the lower, versus lapped against the flow with water running into the seam.

1
Radius from the slant height, not the vertical height
2
Element lines at true length, not plan length
3
Seam allowance outside the divisions
4
Flat seam lapped in the direction of the flow
Example numbers from the lesson 3 worked examples. Rules from BCcampus (1 to 3) and UFGS 07 60 00 article 3.1.6.5 (4). Not to scale.

Sources

Glossary

Pattern fault
An error in the flat layout, such as a height used for a slant height or a plan length used for a true length, that makes the formed piece the wrong size.
Arc check
Comparing the length of a radial line pattern's arc with the circumference it must form; if they differ, the pattern is wrong.
Quality control checklist
A written list of points to be observed during sheet metal work; the optional field quality control article (3.5) of UFGS 07 60 00 requires one and daily documented observations.