Definition
CAD (computer-aided design) is software used to create and edit a part's 2D or 3D geometric model. In manufacturing, the 3D CAD model is usually the source both the drawing and the CAM program are derived from, even when the drawing remains the contractual reference.
Why the model and the drawing can disagree
A factory's CAM programming and process planning normally work from the 3D CAD model directly, not by re-measuring a printed drawing, which is why a mismatch between the model and the drawing (an out-of-date model, a missed drawing revision) is a real and recurring risk.
How CAD relates to the drawing
Not itself on the drawing; the drawing is typically a 2D or annotated 3D derivative of the CAD model, produced for communication and, in many cases, contractual reference.
Common mistakes
Assuming the CAD model and the drawing are always in sync. A model can be updated after a drawing is issued, or vice versa, and reconciling which one is authoritative is exactly the problem model-based definition tries to solve.
A factory's CAM programming and process planning normally work from the 3D CAD model directly, not by re-measuring a printed drawing, which is why a mismatch between the model and the drawing (an out-of-date model, a missed drawing revision) is a real and recurring risk.
See how Blake reviews a partFrequently asked questions
Is the CAD model the same as the drawing?
No, the drawing is usually derived from the CAD model for communication and reference; they can drift out of sync if one is updated without the other.
Does a CNC machine read the CAD file directly?
No, CAM software converts the CAD model's geometry into toolpaths and NC code; the CAD file itself isn't executed by a machine.
What happens if the CAD model and drawing disagree?
It becomes a judgment call for the work preparer or engineer about which one governs, unless the contract or a model-based definition explicitly resolves it.