Hi Everyone,
Many times I see it suggested to not grind the edge on a knife prior to hardening it, leave it still about 1mm at the thickest part and sharpen afterwards.
Indeed in my own experience hardening a knife that already has an edge means I had to sharpen past the thin edge (which didn't harden properly) to get to the harder steel underneath.
The only reason I can think of (in regards to simple heat treating) for really thin steel prior to heat treating being a bad practice is that the thin steel is really quick to gain and lose heat meaning that while the rest of the knife is still coming up to temperature in the forge, the thinnest parts may already be beyond the optimal temperature, experiencing grain growth.
And then when it's time to quench the blade the thinnest parts don't hold their heat as well moving from the forge to the quenchant and may therefore be cooling down to below the optimal temperature before being quenched, resulting in softer steel.
Is this correct?
Additionally, when someone is making a really thin piece, such as a japanese style kitchen knife or a hollow ground straight razor, how close to finished shape do they get these before heat treating.
A really thin japanese knife for example with just one bevel would have about 1-2 cm of steel (measured from edge to spine) which would be considered as "too thin" for hardening wouldn't it?
Do they grind the whole face of the blade more after heat treating?
The same with hollow ground straight razors, do they end up taking a lot of metal away after hardening?
Or is there a trick to heat treating very thin steel that can't be done with a simple "it looks orange and isn't magnetic any more, put it in the oil" method?
Many times I see it suggested to not grind the edge on a knife prior to hardening it, leave it still about 1mm at the thickest part and sharpen afterwards.
Indeed in my own experience hardening a knife that already has an edge means I had to sharpen past the thin edge (which didn't harden properly) to get to the harder steel underneath.
The only reason I can think of (in regards to simple heat treating) for really thin steel prior to heat treating being a bad practice is that the thin steel is really quick to gain and lose heat meaning that while the rest of the knife is still coming up to temperature in the forge, the thinnest parts may already be beyond the optimal temperature, experiencing grain growth.
And then when it's time to quench the blade the thinnest parts don't hold their heat as well moving from the forge to the quenchant and may therefore be cooling down to below the optimal temperature before being quenched, resulting in softer steel.
Is this correct?
Additionally, when someone is making a really thin piece, such as a japanese style kitchen knife or a hollow ground straight razor, how close to finished shape do they get these before heat treating.
A really thin japanese knife for example with just one bevel would have about 1-2 cm of steel (measured from edge to spine) which would be considered as "too thin" for hardening wouldn't it?
Do they grind the whole face of the blade more after heat treating?
The same with hollow ground straight razors, do they end up taking a lot of metal away after hardening?
Or is there a trick to heat treating very thin steel that can't be done with a simple "it looks orange and isn't magnetic any more, put it in the oil" method?
