In parametric CAD programs, the software tracks the changes and allows the user to change earlier steps, and then the software reapplies the layer transformations or actions. Like building a model out of wood, where you want to change shapes at the bottom of the model, the user has to remove all of the wood structures constructed on top of this base. In many of these direct manipulation programs, once a step is complete, combining two items and then using a third object to model a hole in the combination, the user is unable to go back to the first step and make a change. Some CAD programs start with standard 3d shapes cubes, cones, pyramids, spheres, and more, and the user manipulates there objects by combining them to create the model.

Why parametric CAD, and what is it? A simple definition of computer-aided design programs that use computer software to create 3d dimensional objects and plans divides these programs into two types. This series will teach FreeCAD to anyone interested in learning how to prepare 3d models from scratch for fun or profit. While I have covered FreeCAD in the past, I have not created a series of videos that teach regular people about parametric (more on this in a minute) computer-aided design (CAD) from the very first step to advance techniques.

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