After the spline sections are clamped to the former board, shoot screws in to hold the radius.

This photo also shows a method I was fond of at the time - spline ends cut at 45 degrees. The idea there was to spread the weak spot of a joint over a longer area. This approach SEEMED to be more effective than a normal butt-end, but later I decided that it was a non-issue when using former boards to construct a curve.