Modeling three-dimensional solid features often begins with creating a two-dimensional sketch that defines a portion of the shape of your part. Sketching involves the creation of lines, arcs, circles, and dimensions. They are familiar steps to anyone who has created a drawing in a CAD product. Autodesk Inventor's sketch commands look and feel like the two-dimensional geometry commands you used previously. Autodesk Inventor sketch geometry captures relationship information as it is being created. The key difference is that these relationships (or constraints) make the inevitable editing process much easier and more predictable when they are applied correctly.
In the 2D design world, it is possible to create geometry in any sequence because you are responsible for tracking the meaning of the geometry. The 3D modeling sequence resembles the creation of the physical part and the creation of one feature usually depends on a previous feature. This feature hierarchy allows the computer to track the meaning of the geometry. For example, when creating a 2D drawing, first create a circle that represents a hole followed by a rectangle that represents the stock in which the hole is placed. This sequence does not work while modeling in 3D because to place the hole, you must first have a model into which you plan to place the hole.
Assembly designs are often started using a technique called top-down design (or skeletal modeling). You can begin the solid modeling process using sketches that represent some (or all) of the parts in your assembly. Individual part models are then created using geometry from a single sketch in the context of the assembly model. Assembly models are also frequently created using a bottom-up approach in which previously created part models are placed together to represent the final assembly.
When the addition of features (or components) to your model is complete, it is time to create the traditional three view drawing. Views of your model are arranged on your drawing sheet. Because you have a solid representation of your model the system knows which edges to display as solid or dotted in each of your drawing views. Dimensions in your drawing can be manually applied. You can also import the dimensions you placed on your model sketches and use them in the appropriate drawing view. Because the drawing uses placed views of your model any changes that you make to your models are automatically reflected in your updated drawings.
Other tools allow you to take advantage of the power of your computer while assisting you with the functional aspects of your design. These tools allow you to verify the engineering integrity of: bolted connections, shafts, gear train designs, bearing life, springs, and structural loads all using three-dimensional models and design parameters unique to your design.
Both the drawing and modeling approaches to design result in a familiar engineering drawing. In the 2D approach, the drawing captures the physical information needed to create the part. In the solid modeling approach, the drawing is one of several uses for the created model.