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I Forge Iron

why is a softer hardness better for woocuttig tools?


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I constantly read that bronze/straw oxide color is for cutting metal and blue/purple is for cutting wood. But why wouldn't full hardness be just as good for woodcutting? I get that a softer metal is easier to touch up, but wouldn't a harder edge last longer and wouldn't your time investment in sharpening be proportional to the longevity of the edge at the end of the day? What gives?

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you have to take into account the included angles of your cutting edge and what it's for.   Pretty sure that a cold chisel can get away with being harder and a bit more on the brittle side due to the angle of the cutting edge and the support that that offers.  A feather fine edge will be more prone to chipping the harder it is.

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Certainly I keep my carving tools on the light to medium straw tempers!  Things like axes can be a bit softer to allow for impact strength... but I am more likely to use a slightly lower carbon alloy for those... so I still temper them pretty hard!  I would give very different advice from what you've been reading!

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I have a suspicion that this is an old principle dating to the days before powered, even foot powered, grinders were common. Go to a junk shop and find a chisel with a badly chipped edge. Now, using nothing more than a sharpening stone and perhaps a jig, grind the chisel until a flat primary bevel is achieved. It takes a long, long time. I could be wrong but it certainly seems plausible. A softer edge that would be more likely to roll than chip badly would be a more easily remedied failure.

Similarly I've seen people worry themselves to death when sharpening drill bits, even though the bits in question were HSS. Folks will tell you to cool a drill often while sharpening so that the temper isn't ruined, despite the fact that HSS is engineered to maintain its hardness at much higher temperatures than simpler steels. Dunking serves to keep the drill at a temperature you can comfortably hold, not to protect the drill from overheating. A century ago overheating the drill could well have ruined it.

It seems like knowledge from past generations that is no longer applicable given our modern situation.

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Most of the old blacksmithing books were written before World War I, and so the common materials available were (1) wrought iron and (2) simple steels consisting of pure iron with various amounts of carbon. They were 99% of what a smith would encounter. The last hundred years has given us thousands of steel alloys of various contents, and new wrought iron has not been made in 60 years.

The way you had to forge wrought was at a white welding heat: square to octagon to round, or it would delaminate. You also could not drill or punch holes across the grain without weakening the structure, you had to split and drift all holes. Mild steel needs to be heated to no more than a bright yellow, and can be drilled, punched or deformed in any manner you wish.

Trying to use the old methods of quenching and tempering on unknown alloys of steel is a roll of the dice at best. Start with a known material, and look up the recommended heat treatments somewhere. Knifemaker forums are filled with stories of learning what alloys work best for various uses, how to achieve the best blade profile for the task at hand, and how to heat treat for maximum performance.

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