Make Duplicate Curves with a Spindle Sander
A spindle sander can be used to duplicate curves with crisp edges, similar to a router equipped with a flush-trimming bit. However, the spindle sander is longer than a router bit and can shape much larger workpieces than is possible with a traditional template and router combination.
To use a spindle sander for pattern sanding, make an auxiliary table for the sander and attach a half-circle wooden bushing to it. Don’t be too precious about the bushing. It just needs to wrap around the spindle without touching it and be as smooth and even as possible on its outside diameter. Now bandsaw the workpiece to rough shape. Use double-sided tape to attach the workpiece to a template cut in the shape of the desired curve. Then push the workpiece into the spindle sander and move across the spindle. The template will hit the bushing when the shaping is finished.
Drawing: Jim Richey