A method of continuously casting thin strip by controlling roll crown comprising the steps of: a. assembling a caster having a pair of counter rotating casting rolls with a nip there between capable of delivering cast strip downwardly from the nip, each casting roll having a casting surface formed by a cylindrical tube having thickness of no more than 80 millimeters of a material selected from the group consisting of copper and copper alloy, optionally with a coating thereon, and having a plurality of longitudinal water flow passages extending through the tube; b. positioning two expansion rings within and adjacent the cylindrical tube, each expansion ring centerline being spaced within 450 mm of edge portions of the cast strip formed on opposite end portions of the casting rolls during a casting campaign, the expansion rings adapted to increase in radial dimension causing the cylindrical tube to expand changing roll crown of the casting surfaces of the casting rolls and thickness profile of the cast strip during casting; c. assembling a metal delivery system capable of forming a casting pool supported on the casting surfaces of the casting rolls above the nip with side dams adjacent to the ends of the nip to confine the casting pool; d. positioning at least one sensor capable of sensing at least one of the following properties: - the thickness profile of the cast strip downstream; - the local thickness of the cast strip at a defined spot close to the cast strip edges; - the casting roll surface crown during the casting campaign; - the radial casting roll expansion at a defined spot close to the cast strip edges; and generating digital or analogous signals indicative of at least one of the above mentioned properties of the cast strip; and e. controlling the radial dimension of the expansion rings responsive to at least one of the digital or analogous signals received from the sensor to control the roll crown of the casting surfaces of the casting rolls during the casting campaign. a. assembling a caster having a pair of counter rotating casting rolls with a nip there between capable of delivering cast strip downwardly from the nip, each casting roll having a casting surface formed by a cylindrical tube having thickness of no more than 80 millimeters of a material selected from the group consisting of copper and copper alloy, optionally with a coating thereon, and having a plurality of longitudinal water flow passages extending through the tube; b. positioning two expansion rings within and adjacent the cylindrical tube, each expansion ring centerline being spaced within 450 mm of edge portions of the cast strip formed on opposite end portions of the casting rolls during a casting campaign, the expansion rings adapted to increase in radial dimension causing the cylindrical tube to expand changing roll crown of the casting surfaces of the casting rolls and thickness profile of the cast strip during casting; c. assembling a metal delivery system capable of forming a casting pool supported on the casting surfaces of the casting rolls above the nip with side dams adjacent to the ends of the nip to confine the casting pool; d. positioning at least one sensor capable of sensing at least one of the following properties: - the thickness profile of the cast strip downstream; - the local thickness of the cast strip at a defined spot close to the cast strip edges; - the casting roll surface crown during the casting campaign; - the radial casting roll expansion at a defined spot close to the cast strip edges; and generating digital or analogous signals indicative of at least one of the above mentioned properties of the cast strip; and - the thickness profile of the cast strip downstream; - the local thickness of the cast strip at a defined spot close to the cast strip edges; - the casting roll surface crown during the casting campaign; - the radial casting roll expansion at a defined spot close to the cast strip edges; e. controlling the radial dimension of the expansion rings responsive to at least one of the digital or analogous signals received from the sensor to control the roll crown of the casting surfaces of the casting rolls during the casting campaign.