Hand Tools

Subject:
The only real criteria
Response To:
Re: The real story... ()

David Weaver
..for flatness is being able to get to the burr on the back side of a chisel or plane blade. If something is rounded sharply on the back of a blade (not uncommon in older tools), then that's failed. If the last 1/2 or 3/4ths inch of a chisel is slightly out of being planar with the rest of the back but is otherwise functionally fine, the cut is long well established before the abraded part is all the way in the wood. Plenty of japanese chisels are made so that only the last 1/2inch or so of the edge registers on the stone (they're convex on the back a little bit) and they work great because we're looking at the cut while we establish it and making tiny adjustments to get a result.

the HF chisels that I pictured above are about 8 thousandths hollow in the back, but most is just near the bolster. for 5 out of 6 of them, flattening the first 3/4ths of an inch takes about a minute because of this probably unintentional bias. It would be difficult to find a fixture that would make them unworkable because they're already not that long. The hollowness is probably only 2 thousandths or so in the first 2 1/2 inches of chisel blade. It's something you can actually see but would have a bear of a time showing to cause poor work.

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