SolidWorks 2011 Parts Bible - Matt Lombard [305]
FIGURE 23.14
Editing limitations with direct editing
If you change the bottom square area such that the flat face between the bottom square and the arc disappears, you cannot get it back by just moving the face back to where it was; you would have to move the face and then make a cut to reinstate the flat face. This limitation is less serious when the direct edit tool is just another tool within a history-based modeler, because you can resort to the more powerful history-based tools to compensate, but with a dedicated direct edit–only tool you will be up against a more difficult task.
Other limitations of direct edit–only CAD software are going to center around features that themselves are some sort of process, such as fillets or shells. While fillets and shells are two of the most problematic features for history-based modeling, they are also two features that create the biggest limitations for direct edit software.
Using SolidWorks Direct Edit Tools
So how does SolidWorks, a history-based system, incorporate the advantages of direct editing techniques, which are not typically thought of as history-based? What does it look like when contradictory regimes collide and start sharing ideas? SolidWorks has taken ideas from a history-free scheme and incorporated them into a history-based scheme.
First, I will show you how this works in a simple example. Using the part from Figure 23.14, Figure 23.15 shows the FeatureManager and the original sketch. Notice that the original sketch has not changed, but the part itself has. Rolling back eliminates the Move Face features, and making changes to the original sketch changes the starting points for the Move Face features when they are unrolled.
FIGURE 23.15
Direct edits in a history-based part
You may be able to imagine that in a part with a much longer feature tree, where the relationships between the faces and the features are more complex, overriding that complexity by editing a face directly could have some appeal.
Combining direct edit with history
SolidWorks has several features that do not create new geometry, but edit existing geometry only, whether it is native or imported. These include the following:
• Move Face
• Delete Face
• Freeform
• Flex
• Deform
• Draft
• Scale
I'll show you a slightly more complex example. In traditional SolidWorks usage, if you wanted to move the face indicated in Figure 23.16, you would go back and edit the sketch or feature that was used to create it. That would be easy enough, and the fillets would update to match the new geometry.
The direct edit salesmen would say that first finding the feature you need to change is difficult, then waiting for the change to rebuild all the features, and last dealing with the downstream features like fillets that might fail due to the changes is frustrating, and he would be right. (You can find a feature in the tree by right-clicking geometry in the graphics window and selecting Go To Feature In Tree.) The problem is that the part, as shown in Figure 23.16, cannot be changed at all in the traditional direct edit scheme. In the direct edit scheme, the fillets are just faces; they are not intelligent features. If you move faces they are attached to, you have to also explicitly tell the fillet faces what to do.
FIGURE 23.16
Fillets greatly complicate direct editing schemes.
While the direct edit implementation in software such as Solid Edge ST3 is smart enough to make changes to models with fillets on them, the direct edit tools in SolidWorks are less sophisticated and cannot deal with the fillets at all.
Here's how to simplify the part by suppressing fillets and using the Move Face feature to change the part (see Figure 23.17). Here, I've moved the ring around the top of the barrel as well as the mounting boss.
FIGURE 23.17
Using Move Face to extend the length of the barrel