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  • Understanding History-Based Modeling and Dependencies

    Discussion in 'Autodesk Inventor' started by phongnvt, Jun 27, 2017.

    1. phongnvt

      phongnvt Member

      Jul 2016
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      Inventor is often referred to as a history-based modeler, meaning that as you create sketches and turn them into features and then add more features and still more features, each addition is based on a previous feature, and so the model is said to have history. This history is recorded and tracked in the Model browser. The Model browser is a panel that displays on-screen and shows every feature you create during the design of your part. Figure 1.5 shows the Model browser for the pivot link fi le. You can see that each feature is listed in the browser in the order in which it was created, forming a history tree. To create a part that handles changes predictably, you must create a solid foundation on which to build the rest of the model. In most cases, when you are designing a part model you will start with a sketch, much like the one shown back in Figure 1.1. This base sketch will be your foundation, and therefore you must create it to be as stable as possible. Each part, no matter what it is or what it looks like, has a set of origin geometry in the form of the origin planes, origin axes, and a single origin point. You can fi nd these origin features by expanding the Origin folder in the Model browser. Figure 1.5 shows the Origin folder not expanded. If you expand the Origin folder in any part or assembly fi le, you will see the following items:

      • ◆ YZ Plane, the plane that runs infi nitely in the Y and Z directions
      • ◆ XZ Plane, the plane that runs infi nitely in the X and Z directions
      • ◆ XY Plane, the plane that runs infi nitely in the X and Y directions
      • ◆ X Axis, the axis running infi nitely in the X direction
      • ◆ Y Axis, the axis running infi nitely in the Y direction
      • ◆ Z Axis, the axis running infi nitely in the Z direction
      • ◆ Center Point, the point found at zero in the X, zero in the Y, and zero in the Z directions


      When creating the base sketch of a part fi le, you typically start on one of the origin planes. Because the origin plane cannot be edited, deleted, redefi ned, or upset in any manner, this base sketch is inherently stable, and as a result, the base feature you create from it is stable as well. If the second sketch of your part is created on a 3D face of the base feature, this sketch is dependent on the base sketch and is considered slightly less stable than the base sketch. This is because the base sketch could be edited, deleted, or redefi ned in a way that would upset the secondary sketch.
      Understanding how dependencies are created when a sketch and features are based on one another will help you avoid creating a “house of cards” that will fall apart if the base is upset. Although you could base all of your sketches and features on origin geometry to minimize dependencies, it is generally not practical to do so. It should be your goal, however, to keep the number of chained dependencies to a minimum. Assemblies work in much the same way, using the faces and edges of parts to constrain them together and as a result building dependencies between them. Just like part fi les, assembly fi les have origin planes, axes, and a center point that can be used to minimize chained dependencies, thereby creating a more stable model.


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