SolidWorks 2011 Parts Bible - Matt Lombard [304]
Part of the charm of the direct edit scheme was that the software didn't add any information to the model. The model could be transferred between direct edit CAD packages without losing any information. This is clearly not the case with parametric history-based CAD software, where you basically lose the ability to edit the existing model when you transfer it from one parametric history-based program to another. You can add new features, but you can't change what originally appears.
Defining the role of direct edit tools
But direct edit CAD software has not taken over the market, even with all of the recent hype. History-based modelers are still popular with users who design things. There must be more to this story: the direct edit scheme does have some weaknesses. While making individual changes is easy and intuitive, making conceptual changes (changes to the design intent) can be just like starting over again with direct edit. There are also situations in which certain edits cannot be made, or reversing a set of edits does not result in the original configuration. People who are used to the control and power of history-based systems will be less likely to relinquish that control for simple ease of use.
It turns out that the simplified capabilities of direct edit tools are more suited to non-CAD specialists who still need to work with geometrical data either upstream or downstream from the main production modeling. This means that a non-specialist can do the equivalent of a 3D napkin sketch in Sketchup and hand it off to a specialist to create the detailed production model. It means that an FEA (Finite Element Analysis) analyst can make simple edits to a model given to her by a specialist. A machinist can add stock to a finished detail model without being highly CAD proficient. I don't see CAD power users or production modelers giving up history-based CAD software and changing over to direct edit-only tools any time soon.
As a part of the direct edit resurgence, CAD companies have figured out how to apply the concept of parametrics (driving dimensions and geometrical relationships) directly to the solid model, without using sketches or feature definitions as an intermediate step. Also, the history-based modelers are adding some direct-editing functionality. This cross-pollination helps bridge the gap that is now becoming mainly a discussion about how to combine direct edit and history-based modeling techniques. In this chapter, I do not cover the details of how each CAD program has implemented the direct editing scheme; I just want to help you understand where SolidWorks is today in the direct edit spectrum, and what you might have to look forward to as the comparison between the history-based and history-free worlds continues to take shape.
This background information is important as a part of the overall discussion of the place of these tools within the SolidWorks software. Adding direct edit tools to SolidWorks is not an earth-shattering change, but of secondary importance. Notice that the topic of direct edit does not dominate this book, just 1 chapter out of 24. SolidWorks includes the tools because they are useful, not because they are necessary.
Understanding the strengths and limitations of direct edit tools in SolidWorks
Some of the selling points for the direct edit CAD tools are that you don't have to worry about how a part was made (you just make the changes you want to make), and that feature trees with “history” always include feature rebuilds (which users tend to complain about taking a long time, especially for large parts and assemblies).
Without a doubt, grappling with feature order and feature rebuild times are problems that SolidWorks users face daily and often complain about.
Direct edit strengths include:
• Avoid feature order problems
• Avoid rebuild time
• Changes are more intuitive
• Concept of moving faces directly is very intuitive
Probably the most serious