SolidWorks 2011 Assemblies Bible - Matt Lombard [52]
• When possible, it is best to mate all parts to the “ground” part. Creating daisy-chain mates (where A mates to B, which mates to C, and so on) forces the mates to be solved in a particular order, which may take more time to solve. If all the mates relate to established assembly references, the mates may be more stable. Chapter 11 describes using a skeleton in a part to make sketch and feature relations. You can apply a similar concept in an assembly, by mating parts to an assembly sketch.
• When possible, leave part positions fully defined, especially when other geometry is dependent upon the position of parts. Some examples include in-context features, assembly features, or assembly-level reference geometry, which are dependent on part geometry.
• Constraining the rotational degree of freedom for components such as screws, washers, and nuts is usually considered excessive. At times, too many open degrees of freedom may cause problems with complex motion, such as a gripper on the end of a robotic arm. SolidWorks functions well when there is a single, well-defined path between two points, but when there are multiple options, the software may become confused.
• Do not leave errors unresolved in the tree.
• Remember to use subassemblies to break up the number of mates that are solved in the top-level assembly.
• Limit the use of flexible subassemblies.
• Do not mate to entities that may be removed later by suppressing or unsuppressing features, especially edges or faces that are created by features such as fillets. For this reason, it is usually best to wait until parts are complete before you use them to create an assembly, although this is rarely practical.
• Use a degree-of-freedom analysis to prevent mates from becoming over-defined.
Tutorial: Mating for Success
In this tutorial, you will put together a model of a robotic arm to better understand some of the mate issues discussed in this chapter. Follow these steps to mate for success:
1. Open the part named Chapter 5 Robot Base.sldprt from the DVD.
2. In the part document window, click the Make Assembly From Part icon, and click the cursor on the Origin of the assembly to place the part Origin at the assembly Origin. The part is automatically fixed in place.
3. Choose Insert⇒Component⇒Existing Part/Assembly. Click the Browse button in the PropertyManager and find the part called Chapter 5 Robot Tower.sldprt. This part contains a Mate reference to help you mount it to the base. If you bring the cursor near the big circular hole in the base, you can see the preview of the tower snap into place. Click to accept this placement. Figure 5.24 shows this placement in progress. Notice that the cursor appears as a SmartMate cursor for the peg-in-hole mate. When the part is dropped, check the mate list to confirm that a Concentric and a Coincident mate have been applied by the Mate reference.
FIGURE 5.24
A Mate reference being used to SmartMate a component
4. Open the part with the filename Chapter 5 Arm.sldprt, the Default configuration, in its own window, and choose Window⇒Tile Vertically. The part and the assembly should be open in adjacent windows.
5. Click the face inside the hole without the chamfer around it in the Arm part, as shown in Figure 5.25. Then drag it into the assembly to the cylindrical face inside the hole at the top of the Robot Tower part. The concentric SmartMate symbol should appear on the cursor.
FIGURE 5.25
Displaying a SmartMate when dragging between windows
6. Click the green check mark icon to accept the Concentric mate. Move the part to test that the mates are correct.
7. Click the Mate tool on the Assemblies toolbar. Expand the Advanced Mates panel and click the Width mate.
8. In the Width Selections box, select the two inner faces of the Robot Tower part, and in the Tab Selections box, select the outer faces of the Arm part. The selection should look as shown in Figure 5.26.
9.