Paul's hammer trick for flattening irons / blades
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Here is a photo of the finished blade. You can see a rough patch, back from the edge, where the blade was hollowed with a small grinding wheel chucked into a drill. There is more rough area even further back, also from the grinder. The flat area between the two rough areas was once rough, too, so it was part of the high spot. Quite a few cycles of grinding a hollow and flattening on the stone were required to ultimately produce a flattened band at the edge. A bit more polishing is needed, but even as it is, I just took tear out free shavings in hard maple, some figured maple with grain going in multiple directions, and in some tiger maple. Success!
@ed, Yes the thin shiners are the hammer marks. Some in the vertical orientation in the photo and about two rows in the horizontal down the bottom of the photo (some partially obscured by the sticky tape residue). What I have to find out from Paul W. is how did the direction of the slight bend in the plate of the blade affect the orientation of the hammer blow that was given (and I say most strongly that it was a very light hammer, used deftly). The hammer would have been shaped like the cross pein end of a Warrington hammer, but much lighter – perhaps similar to the small cross – pein hammers that LN manufactured.
Paul W will have used the pecking hammer similarly to the technique used to “square up” carpenters stairbuilding squares. If the square had an inside angle less than 90 degrees, you hit the inside of the corner to deform the metal slightly and move the angle out to 90degrees. If the inner angle was more than 90, hit the square on the outside of the corner to move the inner faces back towards 90 degrees. Using multiple light hammer hits on the inside of the curve to reverse that curve and gradually take out the bend. Effectively changing the residual stress in the cutter.Yes, I can see the roughened area on your cutter and the polished area near the cutting edge. I don’t think that you need any more of the cutter polished than what you already have, after all you will have a backing iron covering most of that part of the blade anyway. Only polish that part of the steel further up the cutter when you have to.
Cheers
Mark H@markh Thanks for the info over in ( link ). Yes, I was puzzled, too, by him mixing the grit sizes. I must say, though, that I’ve tried his mixture, and it does work well. By the way, in this case, we know the “600 grit” is 9.5 microns because we know the manufacturer. So, it is a CAMI grit size. By the way, when I said the blade needed further polishing, I meant to refine the existing polish rather than to extend it. You can see that the lapping scratches (parallel to the edge) were not removed by the strop.
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