Areas Suitable for Holding

Establishing areas appropriate for holding or clamping the workpiece, while it is being machined, may be as hard and as important as in case of locating and supporting it. Since the order for establishing the processing areas leaves holding till last, the choice of qualified surfaces can be limited. For holding or champing the ideal surfaces are those directly opposite the locating points. Because those surfaces are the ones that are also most likely to be the ones requiring the machining, the process engineer frequently must affect a compromise. In this case, a resultant holding force should be obtained on other surfaces equivalent to the ideal holding force. It is not always a simple task and without the aid of the part print, it would be almost impossible to resolve in advance.

Some fundamental guidelines for selecting surfaces for holding the workpiece are as follows:

1. Check the print to recognize areas which are to be machined. Avoid using these areas for clamping unless the machining does not include the overall surface.

2. Check surfaces chosen for location. While possible, choose surface for clamping opposite those for location.

3. When the surface opposite the locators must be machined, choose alternate surfaces in such a way that a resultant force can be established that acts against the locators.

4. Choose surfaces which will not cause the clamping action to distort the workpiece.

5. Choose surface areas large enough to distribute the clamping forces. Holding forces concentrated in small areas often mutilate the workpiece. Remember, enough force must be applied to prevent the workpiece from shifting during machining.

6. When possible, avoid using previously machined areas for clamping when there is the possibility that they might become damaged when applying the holding force.