Results of the Survey

Approximately 40 different parts or families of parts were suggested as being candidates for families of parts. Some of these parts did not fit the criteria for families of parts because they have such small family sizes that creating them as a family of parts wouldn't be worth the overhead involved. These small families include electrical components such as resistors and capacitors, and various types of electrical connectors.

One of the most widely suggested groups of families was a set circular connectors defined by a Military Specification, or MIL-SPEC. These groups included inline and panel mount versions, as well as their backshells. Another such group was a family of metal handles used on various types of equipment. These families of handles include a variety of different styles, each of which has a substantial number of members. The most common family, made with round bar stock, has almost 2400 members. The handles are available in three different materials, reducing the number of geometrically distinct parts to just under 800.

There were four basic uses for standard parts among Raytheon users. The first two were visualization and interference checking. For these uses, the important aspects of the model are appearance, outer dimensions, and mounting hole dimensions and locations.

These suggested parts are occasionally used for weight and center of gravity calculations. Elimination of geometric features of the part, such as threads, interior detail, and pins or holes in connectors can drastically affect these types of calculations. If these calculations are necessary, the part has to be modeled as accurately as possible, or the weight and center of gravity of the part have to be determined from another source, and manually entered into the model.

Several important standards and conventions were determined during this survey. Some of these are detailed below.

The global origin should be located at the center of a mounting hole, if there are any. For hardware such as bolts, screws, nuts, and washers, the origin should be on the centerline, at the surface that will meet the panel or other mounting surface. This would be at bottom of the head, near the threads of the bolts and screws. The threads should be created as just a cylinder with the diameter being the major diameter of the thread. The extra effort of creating the threads and the increase in size of the model are not warranted, and having the threads adds no useful information to the model.

For connectors, ignore any pins or sockets. Create the models as if the female connectors had no sockets, and the male connectors had no pins. The connector should be designed to be inserted along z axis, with the axis in the center, and the XY plane on the mating surface. The backshells on the connector should be modeled as the exterior profile for interference checking.

All parts should be inserted along z-axis. Include any mounting holes on the part, as the mounting hardware often has to be shown. If there is a chamfer on the end of a connector, to aid insertion, then it should be modeled as well.

The CADDS5 program allows geometry to be built on any of 256 ``layers'' (0 - 255). These layers can be viewed individually, or as a group. Selected layers can be turned on or off to show different parts of a model or assembly. This is similar to creating a drawing on multiple sheets of clear plastic. They can be viewed individually or multiple sheets can be placed on top of each other to create a complete picture. By Raytheon convention, all entities in a part should be built on layer 1 or above.

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