Tomorrow over at
CADCAMNet we conclude a three-part series on
what makes MCAD products doodoo what they voodoo, or something like that. For the most part, the series boils down to describing the difference between the two leading MCAD technologies, and helping the reader to understand which is best for various tasks. For the uninitiated, it must seem like Spy vs. Spy; the two are fighting but it is hard to understand why.
In today’s marketplace, if you want to buy a top-selling mid-market MCAD product, you can choose from a variety of constraint-driven, history-based products. SolidWorks, Inventor, SolidEdge, and several others all work on the same principle. The geometry on the screen is a reflection of the steps listed in the history (or structure) tree. Every modeling step is recorded, in order, in the tree.

A typical history-based modeler, relentless in its ability to log every piddling detail of how the model came to be; just don’t suggest changes at the last minute.
History-based models have been leading the market for more than a decade, and to a large degree they have defined MCAD. But in recent years 3D modelers that do not rely on a history tree, but allow users to directly define and edit geometry, have been gaining momentum. These products are described by various terms. Rhino uses the phrase “free form modeling;” KeyCreator says “geometry-based design;” and CoCreate says it is “dynamic modeling.”

A typical history-free modeler, a tireless crusader for free geometry. History tree? We don’t need no stinkin’ history tree.
In editing the CCN series, I realized I have a personal bias in this matter. I understand the importance of locking down design intent with a structure tree, but it still comes across to me as control-freak behavior. Give me a free form modeler any day. Unless I’m designing a brake assembly. Or a motor. Or a 10’ mining auger. Or a jet.

Good CAD? Bad CAD? It never ends.
See the problem. It doesn’t matter if I have a personal bias, there is no one tool for the job. No wonder Black Spy and White Spy fought for years, and there was no clear winner. They must have worked for enemy CAD companies.