Autodesk Inventor: Making the Transition from 2D
By Neil Munro
Figure 1: Completed part.
One of the challenges when moving from a 2D environment, such as the one in AutoCAD?, to 3D modeling in Autodesk Inventor? is learning the different thought process required to build rather than document a model. In fact, you may have an easier time of it if you've got little or no 2D AutoCAD experience because you lack the ingrained habits of good 2D designers. The accompanying tutorial, New to Autodesk Inventor?, leads you through planning and creating a simple part model in Autodesk Inventor. The tutorial highlights some of the areas where you may need to think outside the AutoCAD "box" to be proficient with Autodesk Inventor.
Three Words: Planning, Planning, Planning As with most things, a little planning goes a long way. The process of building a 3D part model typically involves a series of operations that either add material to, or remove material from, the model. There are many exceptions to this process, but the following steps comprise much of the workflow for many part models. 1. Create a closed-profile 2D sketch. 2. Add some rules (constraints and dimensions) as to how the sketch entities should behave. 3. Create a 3D solid from the sketch by either extruding the sketch perpendicular to the sketch plane, or revolving the sketch about an axis on the sketch plane.The resulting solid can add or remove material from the part. 4. Repeat as necessary.
The biggest hurdle is often where to start. Well, since the part will be modeled as a series of features, break it down into discreet features. Identify the one shape that best describes the part's form. That shape is usually a great candidate for your first sketch and feature.
Examine the part in Figure 1. What would your choice be for the feature that defines the part? To me, the plate with the chamfered corners is the most obvious feature and would be a reasonable place to start. If you look at the part from the end, an inverted "T" shape might define the part just as efficiently.
Figure 2: Feature breakdown.
Figure 2 shows the part exploded into features. The image on the left shows the part starting with a sketch and extrusion of the plate outline. The image on the right shows the part starting with an extrusion of the T-shaped sketch. The feature created from the initial sketch is shown in gold; features that remove material are shown in red; and the feature that adds material is shown in blue. Note that the bottom rail is not included in the first extrusion in the left image; that's because it's a different thickness than the plate. There are advanced techniques you can use to overcome this, but better keep it simple when creating your first models.
If you were using AutoCAD software to document this part, you would likely start with the view of the face with the chamfered corners. In addition, the view would probably be drawn entirely in the positive XY quadrant of the WCS. It is also likely that you would draw entities from left to right and use symmetry where appropriate. When building a 3D model, using symmetry is important for efficient and robust designs.
Figure 3: Reference geometry.
Figure 4: Dimension value drives sketch geometry.
A new part file contains default reference geometry (planes, axes, and center point). It is good practice to build models around this geometry, aligning critical geometry with the reference axes or center point. You must project reference geometry into your sketch before it can participate in the sketch. Adopting a more "center-out" design philosophy will lead to the creation of robust 3D models.
AutoCAD 2D vs. Autodesk Inventor 2D A drawing view created in 2D AutoCAD consists of precisely created geometry representing edges, points, and so on. To reduce the chance of being frustrated during sketch creation, you have to let go of the good 2D habit that everything must be drawn exactly. Unlike AutoCAD associative dimensions that can track changes to the underlying geometry, dimensions added to Autodesk Inventor sketches drive the size of the sketch geometry. Editing a sketch dimension value changes the size or position of the referenced geometry (Figure 4).
Figure 5: Parallel constraint and horizontal alignment.
Because changing a dimension value modifies the geometry, you can get some interesting results if the value change is large. Sketching roughly to scale reduces the chance of odd editing behavior. Use the following as a guide to editing sketch dimensions.
Modify dimensions in the following order: