> Something that has been troubling me ever since I bought my Japanese > chisel: Starting just a few millimeters back from the sharpened edge, > the entire backside has a hollow ground out. Why? Is that to make > flattening the backside easier? After many sharpenings, the edge of my > chisel is getting very close to the beginning of that hollow. Of course, > as soon as the edge gets right up to the hollow, the chisel dies. Is > this just a feature to sell more chisels? > > Terry Farrell With plane blades, and presumably chisels with a single backside hollow, the beveled side is gently hammered to push the backside out so flattening it will restore the edge. Scary but true. Now I wonder. Why all the extraordinary trouble to mirror polish the back sides of chisels and plane blades dead flat? The control and precision required to fit traditional Japanese joinery is far beyond that needed to notch a bridge, or much of anything else we do to pianos. A notch scoop with only one nominally critical edge is somewhat different from maintaining straight lines and tight fits on three axes in a complicated joint in finish carpentry. And why would a plane blade need a hollow behind the edge under ANY conditions? As friction relief and fine depth control with a freehand chisel used in microfitting joints, yes. In a plane blade that is wedged in a block that handles the cut depth, friction, and presentation angle, what's the hollow for? Virtually all my sharpening is done with a coarse 6" DMT Diasharp "stone" and a steel or ceramic rod if necessary, or a worn out fine grit EZE-LAP (I think it is). Major chisel or plane blade reshaping, in the rare instance of need, is done carefully on the bench grinder with a coarse wheel. My notching chisel has an intentionally slightly rounded back edge (maybe 1mm), because I can steer it better through the scoop than a flat backed blade. There is nothing magic about Japanese chisels other than the extremely hard steel that the laminated construction allows at the edge (which is admittedly terrific). The presumed need for a mirror finish on an absolutely flat back, I don't see as valid for the uses we make of them. If someone made laminated long bladed paring chisels with flat backs, I'd likely upgrade my chisel collection. Does anyone? Ron N
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