SolidWorks 2011 Parts Bible - Matt Lombard [103]
The “Base” part of the Extruded Boss/Base is a holdover from when SolidWorks did not allow multi-body parts, and the first feature in a part had special significance that it no longer has. This is also seen in the menus at Insert⇒Boss/Base. The Base feature was the first solid feature in the FeatureManager, and you could not change it without deleting the rest of the features. The introduction of multi-body support in SolidWorks has removed this limitation.
Cross-Reference
Multi-body parts are covered in detail in Chapter 19.
Creating a solid feature
In this case, the term solid feature is used as an opposite of thin feature. This is the simple type of feature that you create by default when you extrude a closed loop sketch. A closed loop sketch fully encloses an area without gaps or overlaps at the sketch entity endpoints. Figure 7.1 shows a closed loop sketch creating an extruded solid feature. This is the default type of geometry for closed loop sketches.
Creating a thin feature
The Thin Feature option is available in several features, but is most commonly used with Extruded Boss features. Thin features are created by default when you use open loop sketches, but you can also select the Thin Feature option for closed loop sketches. Thin features are commonly used for ribs, thin walls, hollow bosses, and many other types of features that are common to plastic parts, castings, or sheet metal.
Even experienced users tend to forget that thin features are not just for bosses, but that they can also be used for cuts. For example, you can easily create grooves and slots with thin feature cuts.
Figure 7.2 shows the Thin Feature panel in the Extruded Boss PropertyManager. In addition to the default options that are available for the extrude feature, the Thin feature adds a thickness dimension, as well as three options to direct the thickness relative to the sketch: One-Direction, Mid-Plane, and Two-Direction. The Two-Direction option requires two dimensions, as shown in Figure 7.2.
FIGURE 7.1
A closed loop sketch and an extruded solid feature
FIGURE 7.2
The Thin Feature portion of the Extrude PropertyManager
You can create the simplest cube from a single sketch line and a thin feature extrude. However, because they are more specialized in some respects, thin features may not be as flexible when the design intent changes. For example, if a part is going to change from a constant width to a tapered or stepped shape, thin features do not handle this kind of change. Figure 7.3 shows different types of geometry that are typically created from thin features.
Exploring sketch types
You may see the words loop, contour, region, and profile used interchangeably in various areas of the software. In this book I try to standardize some of the more confusing terminology, but in this case, each of the four terms tends to be used in different situations.
FIGURE 7.3
Different types of geometry created from thin feature extrudes
A loop is a selection of edges or sketch entities that touch end-to-end without gaps or overlaps. A contour can mean the same thing as a loop or it may also mean an area enclosed by a loop of sketch entities that may not meet the “touch end-to-end without gaps or overlaps” part of the definition. Contours can also refer to an enclosed area selected for a feature such as an extrude or revolve, as you will see later in this chapter. A region is typically the same thing as a contour, but the term is only found in error messages and is probably nonstandard terminology left over from previous versions of SolidWorks. Technically, a profile is only