I often find myself trying to chuck a workpiece wider than it is deep, and shorter than the chuck jaws-or needing to be gripped by the tips of the jaws only. Accurate centering-even with loose tolerance-is a challenge. A few workpieces have walked back into the chuck under the pressure of the tool bit. In those cases the material was either very hard, or delicate enough that the full force of the chuck would have distorted or marred the finish.
These stackable spacer plates were my solution. The chuck jaws slide in the slots, and the inner end of the workpiece can rest against the spacer's face. I was lucky that my scrap box had some pieces of very precisely ground hard aluminum plate. The diameters were turned on a mandrel that fit the center hole of the spacer. The three smaller holes held alignment pins that kept the parts together when I drilled and band-sawed the three slots.
All images and text Copyright Dale Austin, 1962-2008