First Draft of The Methodology

After the second family was completed, the information gathered from the creation of the first two families was used to create a first draft of the ``How to Create Families of Parts'' document. (See Appendix C for the final document, ``Creating Families of Parts''.)

The document begins with a short overview of important points that designers may not normally consider when making parts, but can make a large difference in Family of Parts performance. This includes such things as database size, number of variables, robustness of the model, and how well it handles out-of-range dimensions in the _tbl file.

Following this is a list of criteria that a group of parts should meet in order to be created as a family of parts. Some of the criteria used for selecting the initial group of parts are included in this list. However, some of those criteria were specific to selection for this project, and so were not included.

The next section is a collection of pitfalls, how to avoid them, and suggestion of things that should be done before entering CADDS so as to minimize the amount of work necessary to create the family. Some of the most important suggestions from this section are summarized below.

1. Before a design for a part is created, the part needs to be studied to determine which of the geometric features are necessary and which can be ignored. Eliminating unnecessary features from the model can often substantially decrease the size of the family and model without hurting their usability.
2. The given dimensions can be very helpful in determining what method to use in creating the part. A method that uses the given parameters directly will generally be more efficient than one that uses many calculated or derived parameters.
3. When entering points, avoid using location parameters, which specify the absolute coordinates of the point, as much as possible. They decrease the flexibility of the model. Also, points should be referenced such that the fewest number of parameters are necessary to control the position. When it is desired that the part be able to be moved with respect to the origin, only one point in the model should be referenced from the origin, and all other points be referenced from other locations of the model, such as the center of an entity or a vertex.
4. Determine how each point is to be referenced before starting to build the part. A plan that is drawn out ahead of time can save much time and many rebuilds later on.

Finally, there is a set of instructions on how to prepare the _tbl file. It also included several pitfalls that were encountered while creating the previous two families.

Once this first draft was completed, it was used in the creation of the third and fourth families. More information was added and current information was revised while creating these two families.

Last Modified: Wed Aug 28 14:41:29 EDT 1996