3D CAD Modeling

Different kinds of CAD call for different ways of thinking about how to use them and how to create virtual parts.

Many companies make entry-level 2D systems, and some of them are even open source or available for no cost at all. Since these can be modified as needed during the final draft’s creation, they offer an alternative to hand drafting that eliminates the need to worry about scale and placement on the drawing sheet.

3D wireframing is essentially a 3D version of a 2D drawing (not often used today). It’s up to the artist to draw each line. The finished product has no mass properties and can’t have holes or other features added to it directly. Although many 3D systems allow using the wireframe model to make the final engineering drawing views, the operator approaches these in much the same way as 2D systems.

The creation of these 3D “dumb” solids is very similar to the manipulation of physical objects (not often used today). Solid volumes are assembled or subtracted from standard 3-D geometric shapes (prisms, cylinders, spheres, etc.) in much the same way that one would assemble or cut physical objects. The models can be quickly converted into projectable two-dimensional views. Most standard implementations of 3D solids lack the necessary controls for freely moving parts, limiting their range of motion, and detecting collisions.

There are two types of 3D solid modelling

Parametric modelling

enables the user to make use of “design intent.” It’s possible to alter the final product. Making alterations to the original design process is a viable option for future tweaks. The operator should place features in the model from the part’s center if that is how the feature was originally intended to be placed. Any available geometric object in the part could be used to locate the feature, but doing so would be counter to the design goals. The parametric modeler can make adjustments to the part while keeping its geometric and functional relationships the same if the operator designs the part as it functions.

Direct or Explicit modelling 

enables geometry to be modified without resorting to a revision history tree. Once a sketch is used to generate geometry in direct modelling, it becomes part of the generated geometry and the designer can make changes to it without referring back to the original sketch. Analogous to parametric modeling, direct modeling can incorporate connections between carefully chosen geometries (e.g., tangency, concentricity).