Features are really just like steps in building a part; the steps can either add material or remove it. However, when you make a part on a mill or lathe, you are only removing material. The FeatureManager is like an instruction sheet to build the part. When you reorder and revise history, you change the order of operations and thus the final result.
Sketching with Parametrics
You have already seen that sketching is the foundation that underlies the most common feature types. You will now find that sketching in parametric software is vastly different from drawing lines in 2D CAD.
Dictionary.com defines the word parameter as “one of a set of measurable factors . . . that define a system and determine its behavior and [that] are varied in an experiment.” SolidWorks sketches are parametric. What this means to you as a SolidWorks user in a practical sense is that you can create sketches that change according to certain rules, and maintain relationships through those changes. This is the basis of parametric design. It extends beyond sketching to all of the types of geometry you can create in SolidWorks.
In addition to 2D sketching, SolidWorks also makes 3D sketching possible. Of the two methods, 2D sketches are by far the more widely used. You create 2D sketches on a selected plane, planar solid, or surface face, and use them to establish shapes for features such as Extrude, Revolve, and others. Relations in 2D sketches are often created between sketch entities and other entities that may or may not be in the sketch plane. In situations where other entities are not in the sketch plane, the out-of-plane entity is projected into the sketch plane in a direction that is normal to the sketch plane. This does not happen for 3D sketches.
You use 3D sketches for the Hole Wizard, routing, and weldments, among other applications such as complex shape creation.
For more information on 3D sketching, please refer to Chapter 31.
For a simple example of working with sketch relations in a 2D sketch, consider the sketch that is shown in Figure 1.19. The only relationships between the four lines are that they form a closed loop that is touching end to end, and one of the corners is coincident to the part origin. The small square icon near the origin shows the symbol for a coincident sketch relation. The setting to enable or disable these sketch relation symbols is found at ViewSketch Relations.
If you drag any of the unconstrained corners (except for the corner that is coincident to the origin), the two neighboring lines will follow the dragged endpoint, as shown in Figure 1.20. Notice the ghosted image left by the original position of the sketch. This is helpful when experimenting with changes to the sketch because you can see both the new and the old states of the sketch. The set- ting to enable or disable this ghosted position is found at ToolsOptionsSketchGhost Image On Drag.