A screw machine focuses on small diameter parts and higher quantities. In many cases the diameter of a Screw Machine Part is less than 1″. These parts are called Turned Parts. When turned parts are high-precision, very small diameter, or highly complex, they are usually made on a CNC Swiss Screw Machine. Swiss Screw Machines have very precise mechanisms for cutting very close tolerances.
To achieve an extremely high-precision diameter on a round bar, the surface is ground to exacting dimensions by a grinding machine. Sometimes a Screw Machine will cut a turned part to get it within a certain tolerance, and then the parts are sent to a grinding house to finish of the surface with a grinding machine, to get a very tight dimensional tolerance. In other cases, the raw bar material will be sent out to a grinding house in 6ft. or 12ft.lengths, for grinding to very close tolerances, before the Machine Shop cuts the bar into shorter pieces with chamfers at the end of each piece. This is done for motor shafts, Dowell Pins and other parts.