Abstract: A frame is designed for temporarily supporting a horizontal plate-like workpiece until it undergoes a vertical translation between guiding and squaring stops, which frame is located in a machine. The frame comprises lateral retractable supporting surfaces which are either edges of a horizontal flat bar or sides of a horizontal flat bar. When the supporting surfaces are the edges of the horizontal flat bar, the bar is mounted so that it can be moved from a straight line position retracted from the supporting of the sheet to a curved position for supporting the edge of the sheet. The bars can also be positioned utilizing the side and are moved either by pivoting or by a four-bar linking arrangement between the retracted and engaged positions. Finally, the bars can be mounted for rotation along one edge between the engaging and retracted positions.