Eliminate the excessive pressure with springs

         Springs are very common components in fixture design. Their capacity to absorb energy is very useful, especially when this energy is larger than the permissible one. Various factors constantly modify each workpiece set up which is causing micro irregularities in the final result. If a clamping fixture was wrong designed then a few more negative factors will be added to fixture-workpiece stack-up. Some examples are the workpiece distortion from over clamping, the distortion of the fixture it self, and the wear of the fixture kinematical elements. The wear of the kinematical elements is very common in fixtures which contain linkages like the toggle clamping fixtures. The toggle clamping fixtures produce large clamping loads when the moving links form a straight line. It is a common practice to allow them to go slightly beyond that line in order to prevent vibration from creating an unwanted unclamping action. A large part of the produced loads is applied through the moving links to the fixture connecting parts (pins, pivots, etc.), so some toggle clamps have a built-in spring to avoid this excessive amount of clamping pressure. Components like the push-pull spring loaded link (see figure below) are made in various sizes (from small to large ones) in order protect the fixture structure and to facilitate the clamping action.   

 
Modifications of the push-pull spring loaded link are used as workpiece pushers or as constant pusher (or pullers) for the fixture links. The link pusher always forces the fixture link in its rest position (or the workpiece insert position). Workpiece pushers are adjusted for clamping the workpiece with specific clamping load (see figure below).