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Dimensional inspection and tolerances · Lesson 4 of 4

Dimensional inspection and tolerances: defects, verification and case study

Defects an inspector catches, why oil canning is judged by the contract, how to record a check, and a worked case study with its findings.

You will be able to: Recognize the common dimensional defects, decide between re-measuring, holding and remaking against the order, and record the evidence a reviewer needs.

9 min · 10 slides · 7 questions

All lessons in this module
Slide 1 of 10

Defects to catch

The defects this module checks for:

  • Thickness out of band
  • A leg off its drawn length
  • An angle open, over-bent or bent the wrong way
  • A hem on the wrong end or face
  • A hem return under 0.375 in
  • Painted side reversed
  • Length over 126 in or the wrong count
  • Waviness or a scratched finish
Four inspection mistakes, right and wrongFour numbered rows, right on the left with a green tick and wrong on the right with a red cross. 1: a hem folded to the inside face as ordered, versus to the outside face. 2: a leg dimension to the dashed mold line, the outside faces extended to their sharp corner, versus to the inside face of the bend, which falls short. 3: caliper jaws square across the hem, clear of the jaw root and tip, read straight on, versus tilted jaws gripping at the tips. 4: micrometer on flat metal with the ratchet, versus on the bend radius.short1234RightWrongInside, as orderedOutside faceTo the mold lineTo the inside faceSquare, read straightTilted, at the tipsFlat, on the ratchetOn the bend radius

Four rows, right on the left with a green tick, wrong on the right with a red cross. 1: hem folded to the inside face as ordered, versus folded to the outside face. 2: a leg dimension to the dashed mold line, the outside faces extended to their sharp corner, versus to the inside face of the bend, which comes up short. 3: caliper jaws square across a hem, clear of the jaw root and tip, read straight on, versus tilted jaws gripping at the tips. 4: micrometer on flat metal using the ratchet, versus on the bend radius.

1
Hem on the face the order shows (new hems start on the inside face), not the other face
2
Leg measured to the mold line on the outside face, not to the inside face of the bend (and never to the centre of the sheet)
3
Caliper jaws square, part clear of the jaw root and tip, read straight on; not tilted, not at the tips
4
Micrometer on clean flat metal with the ratchet; not on the bend radius
Rules: 1 the order and the FlashDraft hem face; 2 the AFS mold-line convention; 3 Mitutoyo caliper guidance (even force; readings at the jaw root or tip can carry a large error); 4 Mitutoyo micrometer guidance (ratchet, clean flat faces). Not to scale.

Sources

Glossary

Remake
This module's term: making a held piece again to its order. The UCSF specification asks for sections formed true to shape and accurate in size.
Inspection record
This module's method: each measurement with the tool used, its zero check (Mitutoyo), who measured and when.
Face (of a hem)
The side of the sheet a hem folds to; FlashDraft starts new hems on the inside face.