MBD Implementation 10 DOs and 10 DON’Ts – Don’t Skip Critical 3D Dimensions and Tolerances (Part 2)

Part 1 of this topic covered four benefits of calling out critical 3D dimensions and tolerances explicitly in Model-Based Definition (MBD), or the downsides of not doing so. Here let’s look into two more.

Downstream data consumers may not be able to measure adequately and accurately using lightweight viewable tools. Table 1 below compares the wrong and right usages of Adobe Reader measuring tools, and by the way, to get the correct result, two buttons must be pressed in advance in Figure 2: Snap to Planar Face and Perpendicular Dimension. Obviously, these details are prone to misinterpretations and manufacturing errors. Let’s remember this is just a simple screw. Now imagine a modest part with hundreds of features. What would be the chance of mistakes if each and every critical piece of information must be queried every time?

The point of this example is not to get into the weeds or discourage using measurement tools, but to illustrate that both Engineering and Manufacturing, both clients and suppliers have to be extremely careful and well prepared with obtaining critical information on the fly, because the stakes are high and the techniques are tricky. So to avoid this unnecessary layer of complexity, at least at the beginning of an MBD journey, we would be better off to annotate explicitly.

Now let’s think about an overall MBD implementation. We all know change is hard and communication is vital, therefore at least initially, we’d rather over communicate than under communicate. Sufficient and clear 3D dimensions and tolerances can alleviate resistance. We should comfort participants by cultivating this kind of reality and perception: ”My job is much easier with MBD, because I have everything my job needs just like in 2D drawings. Moreover MBD conveys richer information, brings better clarity, and provides more capabilities.”

Please note calling out critical dimensions and tolerances doesn’t mean fully defining an entire model, because not all features are critical, rather, often times only a few are. Military-Standard-31000A (Source: Department of Defense of U.S.A., 2013) outlined three levels of annotations and their use cases as summarized in the table below. In many cases, annotations can be reduced.

With new technologies emerging, explicit callouts may not be necessary anymore where production procedures are seamlessly integrated and fully automated, because machines and software can read implicit model data to drive machining, inspection, and purchasing digitally. There are indeed encouraging applications in this direction today. However, most manufacturers and suppliers are not there yet. As long as human interpretations of 3D PMI are needed, explicit callouts will be a cost-effective safety measure to minimize risks and also drive downstream smart manufacturing applications.

That’s it for now on this topic: Don’t skip critical 3D dimensions and tolerances (Part 1 and Part 2). Please stay tuned to upcoming posts for more on MBD implementation best practices. Next post will dive into the importance of 3D PMI organization and presentation, which matters significantly to a successful MBD implementation to many people’s surprise. To learn more about SOLIDWORKS MBD, please visit its product page. Also welcome to discuss with me at Twitter (@OboeWu) or LinkedIn (OboeWu).