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Power Tools:  Skeletons

Pro/Assembly provides a quick and simple method of assembly using something called a skeleton part.  The skeleton part, just like your own skeleton bones, are a building block for the rest of your assembly.  You can create the skeleton part first, or “on the fly” as you work in your assembly.  The skeleton can then be used to assemble the other components.  By modifying a few simple dimensions of the skeleton, the rest of the assembly can “move.”  This is a great way to exercise the assembly to see if your design is right, to check interference and clearance at different positions, and to demonstrate functionality.

The following pictures show an example assembly built with a skeleton.  The left column shows the tractor body and the boom skeleton in each position, the right column shows the corresponding full assembly.

Figure 1A
Figure 1B
Figure 2A
Figure 2B

Could this be done without a skeleton?  Yes.  However, the constraints for the 6-bar linkage controlling the shovel could become a real nightmare.  What happens when you want to change out one of the parts?

Figure 3A
Figure 3B
Skeletons can include any features you desire, including solid geometry, but are not included in bills of materials, or for calculations of mass properties.  Here is the skeleton part for the boom of the above example showing the datum planes, curves and axes.  These curves, plane and axes are used for assembly of the subsequent assembly components.
Figure 4
Using skeletons can minimize parent/child relationships between parts in an assembly.  It can also allow drastic changes to the assembly without requiring a lot of redefinition.  Here a fairly important assembly member has been deleted, but because the other assembly members reference the skeleton part NOT the deleted member, the assembly regenerates fine.  This is a great way to explore options ... if your boss comes and asks you to put in an I-Beam construction member instead of the Box construction you have.  Simply suppress the Box construction member, and assemble the I-Beam constructed part to the skeleton instead.
Figure 5
There are a lot of little tricks to use with skeletons, and they are useful for a lot of different things.  For more information, look in the Pro/E documentation, and read the article by David Paulson on skeletons coming out in Pro/E Magazine.

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