Warren in Lancaster, PA
>I think those who have trouble understanding this technique are greatly overestimating the amount of curvature that is necessary or desireable. If one is taking a .001 inch shaving and the shaving is somewhat thinner (say .0006} at the edge of the shaving than at the center, he can take advantage of that small discrepancy to make small adjustments in the edge being planed. As Wilbur suggests, we are not talking about big arcs here.

I once inadvertantly insulted a fellow on this forum. He said his irons were perfectly straight across and I asked "how perfect are they?" The truth is that it is difficult to get rid of every last bit of curvature on the edge, especially with hand methods, and that curvature shows up when taking thin shavings. I have not seen a Veritas jig in the Diderot Encyclopedia and I have not seen granite plates in 18th century cabinetmakers inventories. My hunch is that they did not flatten their stones several times an hour and that they had very small curvatures on their plane irons as well.