Bench chisel, 25 degree primary with a 30 degree micro bevel on a 1000 then 6000 waterstone. It comes off the stones sharp enough to pare end grain cleanly, but after roughly two mortises in dry white oak the edge has a visible bright line and cuts like a butter knife. Not chipped, just folded over. Vintage chisel, no idea what the steel is. Am I sharpening it wrong or is the tool wrong for the job?
Second possibility worth ruling out: you may be leaving a wire edge rather than removing it. A wire edge feels shaving sharp for the first ten seconds and then falls off, and what is left behind looks exactly like a rolled edge under a light.
After the 6000, strop on plain leather with a little compound, alternating sides, about ten passes each getting lighter. Then slice through some scrap end grain before you start real work — if it was a wire edge, that first cut takes it off and the edge you feel afterwards is the honest one.
Drag the edge very lightly across your thumbnail at about 45 degrees. A clean edge bites and stops. A wire edge skitters one way and catches the other, because there is a flag of steel hanging off one side.
How do you tell the difference between a wire edge and a properly sharp edge without a microscope?
Vintage chisels vary enormously. Some old cast steel is superb, some was overheated by a previous owner on a dry grinder and is soft for the first few millimetres behind the edge. If the problem persists at 35 degrees, grind back 3-4mm into fresh steel — keep it cool, dunk it often — and see if it behaves differently.
Also check what is under the workpiece. Chopping over a void or on a springy bench lets the wood bounce into the edge on the rebound, which is exactly the kind of load that folds a thin bevel.
@bench_dogged · 2mo ago · 3 replies
Folded rather than chipped, in oak, at 30 degrees, points at the edge being too thin for the work rather than the sharpening being bad. Chopping a mortise is impact work — the edge is driven into hard end grain repeatedly and 30 degrees does not have enough steel behind it.
Take the micro bevel to 35 degrees on your mortising chisel and leave your paring chisels at 30. Two seconds more on the stone and the edge lasts several times longer. You lose a little of that first-cut glide, which does not matter at all when you are removing waste.
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@burr_and_edge · 2mo ago
Did three mortises at 35 last night with no bright line at all. Slightly more effort per blow, entirely worth it.
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@grinder_gremlin · 2mo ago
Same story with hinge mortises in hardwood doors. 35 for anything I hit with a mallet, no exceptions.
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