SolidWorks 2011 Assemblies Bible - Matt Lombard [54]
A much newer, formal assembly feature is called the Layout. The Layout is an assembly-level 3D sketch that displays a specific icon and has some special properties. Although the formal feature and the informal technique have similar names, they have very different functions. SolidWorks users do not often distinguish between the two, and many do not even know there is a difference. In fact, most users are unfamiliar with the Layout feature.
In this book, you will find the word layout used with a lowercase “l” to refer to the informal assembly-based sketch layout method. The formal assembly-based 3D sketch with special properties will be referred to with a capital “L” as a Layout. The Layout icon may also accompany the formal feature.
Using the assembly layout sketch
In SolidWorks, layout sketches are a great way to simulate mechanisms, or locate the major components of an assembly. Figure 6.1 shows three examples of assemblies created with the assistance of an assembly layout sketch.
FIGURE 6.1
Assembly layout sketches can be used in a wide range of applications.
The bicycle example is used throughout this book, and the layout sketch was instrumental in establishing the geometry of the frame. Most of the components of a bicycle are purchased as off-the-shelf items that may come in different sizes but are not custom created for individual bikes. The only parts that are generally custom built for a particular size are the frame and possibly the fork. So to design the frame, you have to lay out all of the data that you are given from the individual components, such as wheels, stem, crank set, and seat. When you put everything together, there are additional pieces of information that determine the frame geometry before the detail design of the frame can be started. You need to know the following:
• The size of the wheels
• The wheelbase (distance between the wheel centers)
• The length of the pedal arm
• The necessary clearance between the bottom of the pedal and the ground
• The head angle (effective pivot angle of the front fork)
• The distance between the center of the crank and the center of the rear wheel
The workflow for using an assembly layout sketch is as follows:
1. Open a new assembly.
2. Create sketches on the standard planes, or create new reference planes (you cannot use sketch pictures in assembly sketches).
3. Mate existing parts to the sketch and reference geometry (bottom-up method).
Alternatively, you can build parts in place using the layout sketches as reference (top-down or in-context method).
This bicycle will be used as an example to show how the frame was developed.
First, you start with the wheels. In this example, you want to design an urban utility bike based on mountain bike components, with dual suspension, but using narrow tires, and that means 26" wheels. You need a certain amount of ground clearance as the pedals rotate, and even clearance between the rider's toes and the back side of the front wheel. You will design the frame to fit a rider who is about 5' 8".
The size information is important because the distance between the wheel centers (wheelbase) creates certain characteristics for riders of different heights. A longer wheelbase generally means a more stable and comfortable ride but is less maneuverable and heavier. In this case, based on other research, you want the wheelbase to be 41".
The above information allows you to create the sketch shown in Figure 6.2.
FIGURE 6.2
Starting the bicycle layout sketch
The next set of information you can put into the sketch has to do with the height of the top bar (which is important when you stand over the bike with your feet on the ground),