3D scanning

A 3D scanner (structured light or laser) measures an object’s surface and produces a point cloud, which is converted into a triangle mesh (STL). It is the fastest way to capture complex geometry, such as freeform surfaces, castings and worn parts, which would take days to measure with hand instruments.

How it works

A scanned mesh is not a CAD model: it records the part as it is, wear and flaws included. To manufacture, the engineer uses the mesh as a reference and rebuilds surfaces and features (planes, cylinders, holes) into a solid model. Scanning also serves inspection: the mesh is overlaid on the CAD and a color map shows the deviation in each region.

Practical example

An imported cast housing needed a new mold. Scanning took two hours; rebuilding it in CAD, with planes and holes snapped to nominal sizes, took two days. The deviation map between the part and the new model confirmed the differences were only shrinkage and flash.

Common mistakes

• Sending the scanner’s STL straight to machining.
• Scanning shiny or transparent parts without preparing the surface.
• Trusting the scan for tight dimensions without checking with a contact instrument.