Work supports, unlike clamps, do not actually exert force on a workpiece. Instead, after adjusting to the location of the workpiece, work supports lock in place and essentially become fixed supports, or rests. The load capacity of a work support increases proportionally as the fluid pressure rises, as shown in the above chart. When selecting work supports, choose sufficient load capacity to resist: (1) machining forces; (2) workpiece weight; (3) clamping forces not resisted by the fixed locators.
When a work support is positioned directly under a clamp, the load capacity of the work support should be substantially greater than the clamping force. A proper load capacity requires the work support to resist both the static and dynamic clamping loads. These dynamic loads, the repeated "hammering" due to clamping-arm momentum, must not be overlooked. For best results and for safety, the load capacity of the work support should be at least twice the clamping force.
Another good idea when clamping above a work support is using a sequence valve to activate the work support before the clamp. This prevents the problem of the clamp building up its clamping force faster than the work support builds up load capacity. The sequence valve delays the clamp's activation until the work support has reached sufficient load capacity.