In order to avoid this common confusion, SOLIDWORKS MBD automatically aligns the label to the width feature size dimension line as shown on the left of Figure 7. A drawing comparison between a width feature as a datum feature (left) and a single face as a datum feature (right). The one shown on the left indicates that datum feature B is the width feature because the label B is aligned with the width dimension line, while the one shown on the right indicates that datum feature B is only a single face because the label is not aligned with the width callout.įigure 6. For instance, according to this standard, the datum feature symbol B in the two figures when compared to Figure 6 conveys two completely different design requirements. Similarly, SOLIDWORKS MBD follows the ASME Y14.5-2009 GD&T standard closely. For example, Johnson Controls estimated significant value benefits with improved GD&T practices in the CATIA MBD environment. Although this issue can occur in both 2D drawings and 3D annotations, some MBD software guides the definitions with built-in GD&T rules to ensure solid practices. This lens barrel case demonstrates the costly downside of ambiguous GD&T definitions. The software then highlights the actual face once a label is selected and automatically aligns the datum symbol to the size diameter and tolerance callout.įigure 5. In this approach, you can select the smaller outer cylinder to define the feature. Figure 5 shows the recommended definition using SOLIDWORKS MBD. This problem could have been easily avoided if the symbol was specifically defined to an intended tangible feature, rather than an ambiguous geometry. Inspecting the total runout by holding the smaller outer cylinder. This ambiguity led to a lawsuit of nearly$8 million.įigure 4. ![]() Now, as shown in Figure 4, the total runout is violated and the part should be rejected. As a result, the smaller cylinder on the right should be spun to inspect the part based on the intent of the design. Unfortunately, the customer held the barrel in the way it would assemble in the lens mount. Inspecting the total runout by holding the convenient larger outer cylinder. If the supplier grabs a convenient feature such as the larger outer cylinder on the left, spins the part, and then inspects the runout, the part is good as what is shown in Figure 3.įigure 3. ![]() An exaggerated example of a machined part. Clearly, the smaller cylinder on the right of the figure was misaligned.įigure 2. Figure 2 shows an exaggerated example of a machined part by the supplier. In the actual production, the supplier inspector didn’t have definitive instructions on how to hold the part. A centerline is theoretical and intangible. The real problem with this part is the datum label attached to the centerline on the customer drawing, because it didn’t specify which tangible feature would serve as the datum feature to inspect the tight tolerance. Figure 1 is a simplified illustration of the part.Ī tight tolerance is fine as long as the product function justifies it. The original part by a customer was a lens barrel in a space telescope on which the opening at the left interfaced with a lens, which is why the total runout tolerance was controlled tightly at 0.0006 inch. This actually turned out to be a million-dollar problem. (Image courtesy of a Tec-Ease GD&T tip video.) We can begin by asking the question: Do you see any problem with the GD&T definition in Figure 1? In the figure, datum symbol A is attached to a centerline and then is referenced in a total runout tolerance.įigure 1. So let’s look into this important topic in this article. Datum features provide similar references in a feature control frame. ![]() When we locate a physical address on a map, we reference the country, state, city and street of the address. Datum features are the foundation of composing and interpreting geometric dimensioning and tolerancing(GD&T) definitions. This SOLIDWORKS MBD forum post provides a recent example. A frequent question about 3D annotations is how a datum symbol can be attached to a centerline, an axis or a middle plane of solid bodies.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |