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Using family tables is an easy way to create multiple versions of similar parts. It is a highly versatile function of Pro/ENGINEER that can be a real time-saver.
How to Rename Dimension Symbols
1. From the menu select Modify, Dimension.
2. Select the part on the screen to display the dimensions.
3. Select the dimension you want to modify.
4. Middle mouse button to accept your selection
5. In the Dimension Properties window, select the Dimension Text tab.
6. Type the desired name in the Name field and change the "D" in the Dimension Text field to a capitol "S". This will allow the name to display on your model instead of the dimension symbol.
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The larger the family table gets, though, the more difficult it is to understand and maintain. One way to reduce the number of variable dimensions that your family table controls is with the use of parameters and relations. In fact, with the methods described below, you can drive an unlimited number of dimensions with a set of relations and a few parameter fields.
The example presented here is a library part of a hex head cap screw. Within a specific screw size, you can have several different lengths while all other dimensions remain constant. These groups of "constant" dimensions can be driven by relations as the screw size changes.
The model utilizes nested family tables in conjunction with relations and parameters to reduce the complexity of the family table. In essence, the family table contains the parameters, whose values activate the relations that drive the dimensions in the model.
To make the process of writing and understanding relations easier, I renamed the dimension symbols and gave them simple, descriptive names (Fig 1).
Figure 1 (image of part)
Within my generic, I started a family table with two instances called COARSE and FINE. Although it separates only the coarse and fine thread screws, this step makes things a bit more organized than lumping them all together in one family table.
Figure 2: Parameters
In each of these instances, I created a second-level family table with an instance for each screw thread size. I then created a string parameter called THREAD_SIZE within my generic and gave it no value.
This parameter will be added to the family table and given a different value for each size screw (instance) within the family table.
Figure 3: Family Table COURSE
As shown above, the value of the THREAD_SIZE parameter is 1/4-20 or 3/8-16 based upon the size of the screw. The value assigned in the family table is then used in the relations in the form of an "if, then" statement to drive the desired dimensions for each instance. Dimensions such as hex size, head thickness, and major diameter will be driven by relations to simplify the family table and to make global changes easier.
Here is a sample of the relations:
HEAD_CHAM = HEX (This controls the size of the head chamfer in relation to the hex size for all screw sizes.)
CHAM = DIA/8 (This makes the end chamfer 1/8 the size of the screw diameter for all screw sizes.)
IF THREAD_SIZE=="1/4-20" (These statements drive dimensions based on their size assigned in the family table.)
DIA=.250
HEX=.437
ENDIF
IF THREAD_SIZE=="3/8-16"
DIA=.375
HEX=.563
ENDIF
Finally, I created a third-level family table under each thread size instance and added the Length dimension to the table. I can then create an instance for every screw length I want in my library.
Figure 4: Family Table HHCS_0_250_20
As you can see, this entire family table of screws was driven by adding only one dimension. All other dimensions are controlled by relations, keeping the family table small and neat.
This is just a simple example of the power of relation-driven family tables. The relations in this part allow you to replace multiple dimensions in the family table with one string parameter. You can also make global dimensional changes more easily. To change the hex size to maximum material condition, for example, all you have to do is change this dimension once in the relations. The benefit of using this technique is obviously even greater in larger parts where you can control many more dimensions. 
Kenneth S. Johnson is an associate industrial engineer at ITT Industries, Engineered Process Solutions Group. He can be reached by email at Kenneth.Johnson@itt.com.
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