The machine table of a plain table is usually made of a phenolic plate with plain surface.
The workpieces can be clamped by double-acting suction cups or via template. Thus, the suction cup as well as the template can be positioned completely freely. Stops for the reference point are mostly available and retractable in the machine table.
A special version of the plain table has openings within the table in regular distances. These are closed by solenoid valves. By using special suction cups with solenoid valves, the valves open automatically, when a suction cup is positioned above an opening. Thus, a main disadvantage of the plain table disappears: By the usage of conventional double-acting suction cups the vacuum hoses always run over the machine table.
A main advantage that can be achieved by using the plain table is the fully free positioning of the suction cup on the machine table. But this causes also a disadvantage: The orientation and exact alignment of the suction cups is difficult, because there is no corresponding raster.
For that reason positioning aids are very important while using this type of table.