Large-diameter thin-walled hollow components some times need to be rounded, or corrected for circularity, in the course of manufacture or repair. Various tools have been used for roundness correction, such as expanding split collets and tools having an array of levers actuated by a central plunger. Such tools tend to have considerable mass, and can introduce further distortions into the component to be corrected. Also, known tools tend to fill the interior of the component to be corrected, and so obstruct other measuring or machining operations.
Split collets have been used which have an annular expander core which reduces obstruction, but the expander core is driven by an array of bolts distributed around it, and these must be tightened in exact unison to ensure equal expansion around the periphery of the split collet.