Reverse engineering

Reverse engineering is the process of capturing the geometry, dimensions and design parameters of a physical object in order to create a CAD model and manufacturing documentation. It is used mainly when the original documentation does not exist or is not available.

Typical applications include making spare parts for older machines whose manufacturer has discontinued them, rebuilding machine assemblies that have no drawings, digitizing historical equipment or tooling, modifying and optimizing an existing part, and creating documentation that allows the part to be made again.

In practice, reverse engineering usually combines 3D scanning (to capture complex geometry), precise contact measurement of critical dimensions, and engineering judgment in interpreting the measured data. A worn part cannot simply be scanned and the result accepted as is. An experienced design engineer has to tell the original geometry apart from the traces of wear.

The output is a parametric CAD model (for example in SolidWorks or as a STEP file), manufacturing drawings with tolerances and, where needed, a bill of materials for the assembly.

Reverse engineering makes sense when you have a working or worn part but no drawing or model for it: a spare part for a machine whose manufacturer no longer exists, a part from a supplier who refuses to hand over documentation, or an older design of your own that exists only on paper.

It is also used to design new parts around existing ones (fixtures, covers and adapters that must fit the existing geometry precisely) and to modify a part that has shown weak points in service.

A scanned shape is not the same as design intent. Wear, deformation and manufacturing inaccuracies of the original easily carry over into the new model. For functional surfaces (bearing seats and fits, threads, sealing faces), the dimensions therefore have to be looked up in standards or derived from the mating parts, and the tolerances set again according to function, not according to the measured value.

Decide in advance what output you need: a mesh model (STL) for visualization or printing, or a parametric CAD model with drawings for manufacturing. The effort for the two differs considerably. Also check whether intellectual property rights prevent you from copying the part, for example a patent or a protected industrial design (a design patent in the US, a registered design in the EU and UK).