Part III: Working with Assemblies
Best Practice
This may be an overly cautious approach, but it can mean the difference between an assembly that works and
one where errors are frustratingly persistent. If you are careful to approach all parts with the degree-of-free-
dom analysis in mind such that any newly added mate does not duplicate any of the degrees of freedom that
are already tied down, you will have fewer assembly mate errors and fewer problems with assembly motion.
This means that instead of having the traditional three face-to-face Coincident mates, you would have one face-to-
face Coincident mate (one translational degree of freedom, two rotational degrees of freedom), one edge-to-face
Coincident mate (one translational degree of freedom, one rotational degree of freedom), and one point-to-
face Coincident mate (one translational degree of freedom). This accounts for three translational and three
rotational degrees of freedom without over-defining any of them.
It is true that SolidWorks internally compensates for over-defined degrees of freedom, but relying on it to do so
and then tempting fate by methodically over-defining all assemblies is a risk that you do not have to take, even
though it is common practice. n
Setting up successful motion
The best bet for creating motion in a SolidWorks assembly is to leave open a single degree of
freedom. This means that there is only one way the part can move, back and forth, by translation
or rotation. Computers in general do not respond well to ambiguity. Dragging an item that might
move in several ways is more likely to cause jerky or hesitant motion.A good example of this kind of problem with motion can be found in one of the sample assemblies
that installs with SolidWorks. I have included this example on the CD-ROM for your convenience,
and it is shown in Figure 13.8. The filename for the assembly is Plunger.sldasm.FIGURE 13.8An assembly displaying best bet for motion
Drag here and the motion is poorDrag here and the motion is smooth