My last two blogs on the topic of model-based definition (MBD) implementations (Part 1 and Part 2) explained the importance of calling out critical dimensions and tolerances. Another best practice from a product perspective is to organize and present 3D PMI clearly because people do judge a book by its cover. In an MBD implementation, we should try to avoid inviting any unnecessary objections ourselves.
Let’s take Figure 1 below as an example. Yes, there are 3D dimensions and tolerances. But how do you feel about this presentation?
Busy, messy, confusing, even frustrating? Some call it “fur ball” or “rat nest,” which is one of the common objections against MBD, resulting in resistance to implementation efforts. Tim with Waters Corp. exemplified it very well in a SOLIDWORKS MBD forum discussion: “One point listed that should NOT be discounted is the capturing of organized, thoughtfully presented 3D views. Just recently, our Core Research team began using MBD, and one of the first parts completed was not presented very well. The views and dimensions were scattered about, in no logical order, and it just looked bad. So bad, in fact, that the machinist ended up creating his own manual sketch on paper to create something he could work with! Not exactly a ringing endorsement of MBD. Fortunately, I was able to clean up the presentation and show the machinist how the data could/should be presented. He was much happier after that.”
Now that we understand the significance of MBD organization and presentation, how should we achieve it? Well, first of all, MBD doesn’t mean automatically throwing away every 2D drawing technique. We need to understand the nature of a practice and select accordingly: Is this 2D practice tied to 2D projection, or paper sheet, or is it still applicable in 3D model space? Here are several examples for these cases: First or Third Angle Projection declaration in Figure 2 may no longer be necessary anymore because this ambiguity is greatly resolved in MBD.
Similarly, Drawing Sheet Zones are not so useful for digital models and PMI thanks to dynamic model manipulations, but may still be necessary in printouts.
However, there are indeed 2D practices still effective and efficient in MBD, view layer being one. For example, from the same perspective, there could be large amount of linear dimensions, angle dimensions, datums, geometric tolerances, notes, tables, hole callouts and so on. View layer is a great tool to categorize and control them. As shown in Figure 3, Military-Standard-31000A in U.S. defines “Each annotation data type should be placed on an appropriate layer and orientation plane corresponding to the view it represents” (Source: MIL-STD-31000A, Department of Defense Standard Practice Technical Data Packages, 2013).
Besides layers, view organizations in 3D are also instrumental in conveying PMI in a presentable, consumable, and actionable way. SOLIDWORKS MBD provides rich and powerful tools to help organize and present MBD data, such as:
- An overview of multiple perspectives all at once in Figure 4;
- Dynamic Annotation Views to fade in and out PMI intelligently according to the viewing direction in Figure 4 (Lower right quadrant);
- 3D Views similar to visual bookmarks on a filmstrip to quickly capture and locate orientations, zooming factors, configurations, display states, and annotation views in Figure 5;
- Model Break Views to improve display efficiency by skipping repeated segments in Figure 6.
Now let’s compare Figure 1 with Figure 4, 5, and 6. Clearly, the fur ball issue is gone and data consumption is much easier now.
My Next blog will look into the differences between graphics (human-readable) and semantic (machine-readable) PMI and their respective significance. To learn more about SOLIDWORKS MBD, please visit its product page. Also welcome to discuss with me at Twitter (@OboeWu) or LinkedIn (OboeWu).