By aliveunwed

It's not pretty

This is my first attempt at blacksmithing, a small kindling cutter called a knife froe.

Made from an old electric lawnmower blade - chosen because the steel can be made tougher and harder than the steel used in things like oven slides or car bodies.  You can see the hole where the bolt attached it to the lawnmower shaft.

I made this as a second prototype and to see what I could do with the tools I already have: hammer, pliers, vice, angle grinder and blow torch.  I found that my blow torch isn't capable of heating more than a few square inches of metal that thick, so hardening would be nearly impossible on anything larger than a small pairing knife.  And the vice has no flat surfaces to hammer on, complicating things further.

When I first heated the metal I could see a colour change in it radiating from the heat source, yellow, then cyan, then blue and dark purple.  This is it losing its hardness.  To get the hardness back you have to heat it until it's red hot and no longer magnetic (very strange) and then plunge it into water or oil.  This also makes it brittle.  Heating it again until you see the colours begin to run - tempering - is a compromise between soft/pliable and hard/brittle.

I was only able to harden the blade edge, but that's all I needed for testing.

You use a froe by holding it in one hand and hitting the top edge with the mallet.  Picture holding a large kitchen knife in your off-hand and driving it down the grain of a piece of wood with rolling pin.  You get kindling the size you want even if you're a lousy shot.

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