Why a CAD model may cost more than 3D scanning

We sometimes get incredulous responses from those previously unfamiliar with CAD modeling costs. It is a common misconception that CAD models are produced automatically from scans. While there are some automated methods to process scan data to a CAD model, the results are useful only in very limited circumstances. Ninety nine percent of the time it is a human that is responsible for the CAD model.

A good example is an an engine block. Think about all the detail … the mating surfaces for all the supplementary equipment, alternator, transmission, cylinder head(s), exhaust, all the bolt holes, and the complexity of the surfaces where no parts are located, (the cast surfaces).

Although there is some additional effort in the scanning to capture additional detail for a complex item such as the engine block, that might take an additional few hours, so it could be done in maybe 3 or fours hours. However, the CAD time could easily be 30 – 50 hours.

The scan result has no distinctions, the points or triangles that make up the mating surfaces are not in any way different than the ones that make up a bolt hole or any other surface. Its is the job of the CAD modeler with the appropriate software and training to assign the specific type of surfaces that are needed in the CAD model. The reason why the specific surfaces are needed is for the CNC machining process. If there’s no surface specified, it can’t be machined efficiently. A CAD model is also preferred for 3D printing as its a lot more efficient to provide a clean file than can be modified later if needed.

The software allows the modeler to fit the specific surfaces to the scan data. A hole for example needs to be a cylinder, so it can have a center. If there’s no center, the hole cannot be drilled on a CNC machine. This is why simply processing the scan to CAD by automated software does not work well. Automated software is currently not smart enough to put the right surface where it needs to be. So it could make something that looks like a hole where there’s a hole in the scan, but it won’t be recognized as a hole because its not a true cylinder.

Every surface and feature of the engine block requires multiple choices by the CAD modeler to generate the appropriate surfaces. The CAD modeler might have to make over 5000 decisions or actions to complete the model using our engine block example. This takes time. Architectural modeling requires similar decisions to be made by a human to create the architectural CAD model. Although the end result is not CNC machining, the downstream processes requires that walls, ceiling, floors, windows, and structural elements are specified. If the these elements are not specified it can be inefficient (or may not be possible) to develop floor plans, analyze the 3D space to estimate material usage, or provide a result that is useful for future processes.

While its true that machine learning and AI are making advances in many areas, CAD modeling from scans is one area where you can’t replace the skilled person that does the modeling (yet).

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