WORK SUPPORTS
Supporting the workpiece is a basic function of any workholder. Although solid supports alone are adequate for some workholders, combining power work supports with solid supports is often a better choice. Hydraulic work supports are sometimes used even with manual clamps. Work supports are available in a variety of types and styles.
Work supports automatically adjust to the correct workpiece height and, once positioned, securely lock. A sliding-fit pressure sleeve holds the plunger absolutely vertical, even while unlocked; therefore the plunger remains stationary during the locking process, so there is no loss of accuracy as the support is locked. This design provides far better accuracy and repeatability than earlier segmented-collet or sandwiched-plate work supports.
Including work supports in a fixture design prevents deflection and vibration caused by the machining forces. As shown above, work supports act as supplements to the three fixed supports. The locators and fixed supports properly position the workpiece. The work supports are then positioned at any points where clamping forces or machining forces can deflect or deform the workpiece. Work supports, like many clamps, can be manifold mounted or plumbed with tubing.
The three primary forms of work supports are the spring-extended, fluid-advanced, and air-advanced actions. Each type comes in several shapes and mounting configurations to meet virtually all workpiece-supporting requirements.
Spring-extended work supports continuously extend the plunger with a light spring pressure. The weight of the workpiece when loaded depresses the plunger to the proper height. The spring force maintains plunger contact with the workpiece until fluid pressure locks the support in place. Once locked, the work support becomes a fixed, precision-height support.
Fluid-advanced work supports are retracted until fluid pressure is applied, for clear loading. Applying fluid pressure gently advances the plunger. Once workpiece contact is made and a preset resistance is reached, fluid pressure locks the plunger at the precise height. Once locked, the work support becomes a fixed, precision-height support. Note: fluid-advanced work supports should not be used to lift loads.
Air-advanced work supports advance the plunger with air pressure. These work supports are much like the fluid-advanced type, that is, normally retracted and advanced as air pressure is applied. Air-advanced work supports are used for fine tuning the contact force, using a simple air regulator. Contact force can be as light as a few ounces. Leaving air pressure continuously on allows these supports to be used as light-force spring-extended work supports.
