Royal Products’ line of CNC expanding mandrels are useful for workholding applications that require access to the entire outer diameter of the workpiece. Lathe drawbar motion expands the mandrel sleeve to grip the part, and parallel sleeve expansion maintains full contact with the workpiece for high holding force and torque transmission. Gripping a workpiece by its inner diameter (ID) rather than its outer diameter (OD) is a workholding option that many job shops fail to consider when turning or grinding parts. However, this technique offers a number of advantages, especially in the machining of workpieces with complex surfaces. Royal Products (Hauppauge, New York) produces a series of CNC expanding mandrels designed for a range of spindle types that it says offers more flexibility in workholding than people might think. According to Tom Sheridan, Royal’s vice president of marketing, expanding mandrels can be used to grip any workpiece that has a suitable inner bore diameter and which lends itself to being completely machined on the outside. The suitability of a workpiece’s inner bore is application-specific; Mr. Sheridan generally advises that there be, at most, a 3:1 length-to...