Dimensioning in a 3-D CAD system

摘要

How important are dimensions to 3-D CAD modeling? Depends on your design objective, I guess. The 3-D CAD software that I frequently use will allow me to model products without using any dimensions at all. The ability to model without dimensions is a characteristic of most of the competing software as well. The result of such free-form modeling may look great, but it really leaves the actual size of the product in a subjective state. If eye-balling it is close enough, then all is well. Some manufacturing processes directly use the 3-D CAD model for programming manufacturing equipment. For example, I've used a "3-D printer" to create plastic models that closely resemble the 3-D CAD model; no mechanical drafting or blueprint was needed. As with other types of "rapid prototyping" equipment, a 3-D printer manufactures a part by depositing thin 2-D layers of plastic to build up the final 3-D shape. Some final sanding and finishing are required, but if all you need is a shape to hold in your hand, this is a pretty amazing tool.