workpiece hold-down clamp are special units in CNC- machining centres, which are to support the available vacuum clamping systems and ensure to properly clamp workpieces within difficult processing conditions.
workpiece hold-down clamp in milling process
workpiece hold-down clamp for the router head are mainly used in the nesting processing, when particularly small or complicated workpieces are to be milled out. Here the vacuum is being additionally supported from the top by circular pressure around the router head.
Because the downholder moves with the router head, the danger persists that workpiece may be laterally displaces through friction between workpiece and downholder. This were the contrary effect to the original purpose.
Hence downholders are usually equipped with an air cushion or balls, which facilitate a frictionless gliding on the workpiece surface.
Dornholder have also been used in the 80´s and 90´s for drilling gears in CNC-machine centers. This was relatively easy to realize by subsiding a panel with the appropriate hole profile around the drilling machine. Because the service of the vacuum pump and the clamping systems significantly increased from the year around 2000 and only vertical forces occur during the drilling in the technical principle, these downholders completely vanished from the marked from around 2000.