The Legacy of 2D

30 Sep, 2002 By: Jeff Wymer

Over the past year I have heard a number of statistics regarding the number of AutoCAD users worldwide, generally reported as being between two and three million. Regardless of the exact number, that's a lot of AutoCAD users. A large number of them use AutoCAD for mechanical and manufacturing design, and are part of a growing trend of 2D users converting to 3D design. This raises concerns over legacy AutoCAD data, as many users have databases consisting of thousands of DWG files. So what can they do with their old 2D AutoCAD drawings?

The answer varies from organization to organization. Often, it depends on a particular company's workflows and requirements. Many businesses, which have made a large investment in AutoCAD customization and automation over the years, enjoy the luxury of maintaining their legacy drawings within AutoCAD, which is installed as part of the Autodesk Inventor Series product. These organizations remain productive with their existing 2D designs while they come up to speed on 3D.

What about those organizations just starting out in 3D that do not have an extensive database of 3D parts and assemblies? Many new designs reuse existing components. In order to get going, businesses are turning to their database of legacy 2D AutoCAD drawings as a starting point for a new 3D design. Autodesk Inventor 5.3 provides users a workflow that allows them to reuse their AutoCAD data to assist in the development of new 3D designs. While the concept itself is not unique, Autodesk Inventor's implementation of the concept is. Autodesk Inventor 5.3 provides functionality, permitting users to continually mine a 2D AutoCAD DWG file.

What Method Works Best for You?
Autodesk Inventor software does not limit or interfere with a natural workflow by forcing designers down a single path while moving from 2D to 3D. Instead, it offers multiple paths, allowing the designer to choose what works best for the task at hand. AutoCAD 2D DWG data can be imported wherever and whenever it is required, whether it is in the 2D drawing-manager environment or directly into a part sketch for use in 3D modeling.

Figure 1. The DWG Import Options wizard provides functionality to filter what data is to be imported and what its destinations will be.

The first method involves importing the 2D AutoCAD drawing into Autodesk Inventor's 2D drawing manager. To do this, use the Open dialog box to browse to the AutoCAD file. Be sure to set the file type to DWG in order to search for only the AutoCAD files within that directory. By selecting the Options button, the DWG File Import Options wizard becomes available, as shown in Figure 1, providing functionality to filter what data is to be imported, and what the destination will be within Autodesk Inventor. Be sure to place a check in the "Constrain Endpoints" checkbox and select "New Drawing" as the destination for this workflow. The DWG data will be imported into a 2D sketch within the drawing manager, referred to as a draft view. Next, promote the dimensions needed to drive the part to the sketch level. This is done by selecting a dimension, right-clicking, and selecting the Promote to Sketch option. When building a 3D model from a 2D drawing, one fundamental rule to remember is that the dimensions used to detail a component are not necessarily the dimensions required to make a solid with proper design intent.

The draft view can be edited by selecting its icon in the browser and pressing the Sketch button. Finally, window-select the geometry and dimensions required to make the next feature on a part, and select "Copy" from the right-click menu to locate it in one of the model's sketches.

The second method of using AutoCAD data involves directly importing the required geometry while in the context of any sketch. Select the Insert AutoCAD File button, as shown in Figure 2, which looks like the icon for a DWG file. This will launch the Open dialog, allowing a designer to browse to the desired DWG file. As mentioned earlier, by pressing the "Options" button, you can filter the required layer data needed to insert into the sketch. Once the data is opened, you can use Autodesk Inventor's 2D move and rotate commands to position the geometry. Repeat this as many times as required until the part has been completed.

Figure 2. When you select the "Insert AutoCAD File" button, which looks like the icon for a DWG file, it will launch the Open dialog-box where you can browse and locate the desired DWG file.

Reusing Consumed Sketches
Once a sketch has been used to create a feature, it is said to be "consumed" by the feature. Often, when 2D AutoCAD geometry is imported into Autodesk Inventor to assist in the creation of a 3D part, there are multiple profiles contained within the sketch. Each profile may be used to create different features. Rather than reinserting the same AutoCAD geometry over and over, the original sketch that is now consumed by a feature can be shared. This is done by selecting the required sketch within the browser, right-clicking, and selecting the share sketch option. A new sketch entry will appear in the browser, directly above the original feature created using the sketch. Now multiple features can be created from this single sketch that originated from AutoCAD. An added benefit of this feature is that all the features are tied back to a single sketch. In other words, multiple features can be modified by making a change to that one sketch!

Is there a Doctor in the House?
When Autodesk Inventor software attempts to create features with imported DWG data, it may find errors that prevent the feature creation from proceeding--items such as open loops, redundant sketch points, or overlapping curves. This is common with many 2D AutoCAD drawings; users don't typically create 2D drawings with the intent to move them to 3D. To fix these issues, Autodesk Inventor has incorporated the Sketch Doctor to highlight sketch errors, describe error types, and suggest solutions, as shown in Figure 3. This unique functionality makes the transition from AutoCAD easier by guiding the user through the error-recovery procedure. To access the Sketch Doctor, right-click while in the context of a sketch and select the "Sketch Doctor" option. The feature-creation dialog box may also indicate sketch issues with a button that looks like a red cross. This button will also launch the Sketch Doctor.

figure Figure 3. The Sketch Doctor identifies, highlights, and describes sketch errors; it also suggests possible fixes and allows you to select the desired solution.

The Sketch Doctor works like a wizard. It first helps identify the problems within the sketches. It may report multiple problems. Upon selecting an issue, the Sketch Doctor will provide more information about this particular problem. Along with a description for the problem, the Sketch Doctor suggests a fix. Next, the wizard provides suggested options, allowing the user to pick the best means of fixing the sketch.

Many mechanical and manufacturing businesses have used AutoCAD in the past to generate the required detailed drawings within the engineering departments. As a result they have a large database of 2D AutoCAD drawings. As these businesses move to 3D design to stay competitive, migrating the legacy data also becomes important. Autodesk Inventor offers flexible tools for reusing 2D AutoCAD data.

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