What Is Model-Based Definition?
Ryan Reid posted on January 28, 2016 |
Get used to MBD and you will wonder why you ever put dimensions on a 2D interpretation of the model.

Model-based definition, or MBD, lets you place the dimensions and notes right on the 3D model.

Tradition is not always bad, but if it gets in the way of truth, it’s time to reconsider. Traditional drafting practices have us creating 2D views of 3D models. On these 2D views, tradition would have us place all dimensions. But if you think of the 3D model as the source, the single truth, then 2D views of it are only interpretations. One mistake, or misinterpretation, and we have a problem. So why did we ever start putting dimensions on 2D views in the first place? We had no choice when we only had paper. Everything had to get flattened into 2D views so it could be put on paper. But now, just about all our designs are in 3D. Is it time to reconsider tradition and put the dimensions right on the 3D model itself? 

What’s Behind the Buzzwords? 
First, let’s get the acronyms out of the way. MBD stands for model-based definition. MBD is very similar to, or a synonym for, PIM, or product information modeling. GD&T is geometric dimensioning and tolerancing. It’s a different way of dimensioning parts in either 2D or 3D. It dimensions features and geometry instead of lines. There are other definitions of it, but I won’t get into that now. 

MBD is the practice of placing either traditional or GD&T dimensions on the 3D model itself during the design process. The engineer or designer can place these dimensions on the model for a variety of uses. Following is a brief overview of why MBD would be used.


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