Step Jaws, designed by the famous Australian woodturner and author Richard Raffan, are used for holding a range of spigot sizes with minimum jaw movement and without the necessity to change the jaws due to its many steps. These Jaws are designed primarily for bowl turning and they are especially useful when roughing out a number of bowls at one time. Boxes are also easily turned using the step jaws. The bottom can be turned by holding the rim without leaving unsightly pressure marks.
The sizes indicated on the drawing are when the Jaws form a perfect circle. VM120 and VM150 chucks provide approx. 48mm of expansion beyond these specified sizes. All steps on these Jaws have an internal dovetail angle of 14 degrees for clamping and an external dovetail angle of 10 degrees for expanding.