an apparatus for calibrating hollow chamber sheet extruded lines out of thermoplastic resin includes a vacuum housing and a planar intake area at a first end of the vacuum housing . the planar intake area is configured to receive the extruded line . support rollers within the vacuum housing are configured to support the extruded line . the extruded line exits the vacuum housing through a planar outlet area located at a second end of the vacuum housing opposite the first end .