SolidWorks 2011 Parts Bible - Matt Lombard [253]
FIGURE 19.16
The Feature Scope panel
The default setting for the Feature Scope is to use the Selected bodies option with the Auto-select option. The All bodies option is essentially the same as using the Merge result option. When the Selected bodies option is selected and Auto-select is unselected, as is shown in Figure 19.16, you must select bodies for the current feature to affect them. New bodies that are added to the model are not automatically added to the list; you need to manually edit the feature and add additional bodies to the list as appropriate.
Using the Rib feature
The Rib feature is hypersensitive to changes to the number of bodies. A rib only automatically merges with a body if it is the only body in the part. If a rib is created in a single body part and then the model is rolled back and an additional body is created before the rib, then the Rib feature will fail when the tree is unrolled. The error that this causes reads, “The rib is not bounded properly. The extension of the rib does not intersect the part model.” Technically speaking, this is true, but like other SolidWorks error messages, that does not make it helpful. The cause of the error is that suddenly the body that the rib is supposed to merge with is no longer identified. The Rib feature does not have an Auto-select option. You can fix this problem by going to the Feature Scope in the Rib PropertyManager to select a body for it to merge with. The Rib feature does not use the normal Feature Scope, because the Feature Scope is intended to select multiple bodies, and the Rib feature requires a single body. There is a simple Selected Body selection box in the Rib PropertyManager.
After you have selected the target body, deleting the new bodies that caused the problem in the first place, thankfully, does not make the problem reoccur. However, if the body that the rib is merged with is split using the Split feature, then that does cause a problem. As a result, the two things that cause the Rib feature problem are rolling back and either adding bodies or splitting the body to be ribbed.
Caution
As you encounter more specialized situations with multi-bodies and dependencies, you may notice more quirks in the SolidWorks internal body management. The next section on managing bodies addresses some of these quirks directly.
Using the Delete Solid/Surface feature
If you have created many ribs in a casting or plastic part, then it may be tedious to go through and repair them all every time the body count changes. This sort of thing happens even if the other body is just a reference body or an unused leftover.
In cases like this, you can use the Delete Solid/Surface feature. This is alternatively called Delete Body, depending on where you look. Delete Solid/Surface removes the body from the body folder (discussed in the section on body folders). This is a history-based delete, which means that before the Delete Body feature in the tree, the body exists, and after the Delete Body feature in the tree, the body does not exist. This feature has no effect on file size, because the data for the body must still exist, and it has little, if any, effect on rebuild time. What is happening is that the body is still there; you just cannot see it and have no access to it.
Delete Solid/Surface is often used for other purposes as well, primarily to clean up a model at the end of the tree. The reasoning is that multiple bodies in a part confuse people. My recommendation here is to remove bodies if they are getting in the way, either for a hyper-sensitive feature like the Rib feature or if they are causing visualization problems.
Creating multi-bodies with the Cut feature
A Cut feature may create multi-bodies, either intentionally or unintentionally. When it does happen, the Bodies to Keep dialog box appears, enabling you to select which bodies you intend to keep. The Bodies to Keep dialog box