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This phase of the fixture-design process requires the most creativity. A typical workpiece can be located and clamped several different ways. The natural tendency is to think of one solution, then develop and refine it while blocking out other, perhaps better solutions. A designer should brainstorm for several good tooling alternatives, not just choose one path right away.
During this phase, the designer's goal should be adding options, not discarding them. In the interest of economy, alternative designs should be developed only far enough to make sure they are feasible and to do a cost estimate.
The designer usually starts with at least three options: permanent, modular, and general-purpose workholding. Each of these options has many clamping and locating options of its own. The more standard locating and clamping devices that a designer is familiar with, the more creative he can be.
Areas for locating a part include flat exterior surfaces (machined and unmachined), cylindrical and curved exterior surfaces, and
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internal features (such as holes and slots). The choice of standard locating devices is quite extensive.
Similarly, there are countless ways to clamp a part, using a wide array of standard clamping devices. For example, a workpiece can be clamped from the top, or by gripping its outside edge or an internal surface.
For preliminary drawings of the fixture, use several colored pencils. Often black is used to sketch the fixture, red for the part, and blue for the machine tool. Use isometric graph paper to keep the sketch proportional.
The exact procedure used to construct the preliminary design sketches is not as important as the items sketched. Generally, the preliminary sketch should start should start with the part to be fixtured. The required locating and supporting elements, including a base, should be the next items added. Then sketch the clamping devices. Finally, add the machine tool and cutting tools. Sketching these items together helps identify any problem areas in the design of the complete fixture. |
