CAD, CAM and shop data exchange · Lesson 4 of 4

CAD, CAM and shop data exchange: defects, verification and case study

The data defects that build a wrong part from a right-looking file, a case study from a coping drawing AFS used to test its reader, a pre-send check that catches them, and the lockout rule for clearing a jam.

You will be able to: Diagnose common data-exchange defects (wrong units, mirrored bends, swapped angle convention, misattributed dimensions, unreadable formats, stale revisions, duplicate sends) and document the evidence and the correction.

11 min · 11 slides · 8 questions

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Slide 1 of 11

Unit scale errors

A unit mix-up between inches and millimetres scales every length by 25.4.

Inches read as millimetres make a leg tiny; millimetres read as inches make it 25.4 times too big, which can push it past the 48 in girth limit, where the limit check catches it. A small error inside the limits is caught only by a known dimension.

Sources

HEADER Section Group Codes (AutoCAD DXF Reference, 2020 help) - Autodesk
NIST Handbook 44 (2026), Appendix B: Units and Systems of Measurement - National Institute of Standards and Technology
AFS fabrication limits - materials, thicknesses, bend rules and sizes the shop can make - Architectural Flashing Supply

Glossary

Mirror image: A profile with the same leg lengths as the drawing but every bend turned the other way, the result of copying coordinates between a y-down and a y-up frame without negating y, or of negating y twice.
Dimension override: Text typed over a DXF dimension in place of the measured value; it can disagree with the drawn geometry.
Revision Compare: An AFS tool that lists what was added, removed and changed between two DXF revisions of a drawing and overlays them.
Servicing (lockout): Under 29 CFR 1910.147, work such as setting up, adjusting, unjamming and tool changes where unexpected start-up or release of energy could injure the worker.