CountryByNet.com Forums :: Re: Grinding knives from files, lawnmower blades, etc.

You fellers may already know this, but it's MUCH easier to grind a file down if you anneal it first, then re-temper after grinding. To anneal, heat with a torch or forge to the point that a magnet won't stick to it, then put in a bucket of wood ashes or vermiculite and leave until it cools completely. This takes the factory temper out, and makes it much softer and easier to work. After grinding to the shape you want, you need to heat treat and temper, or it will be too soft to hold an edge. There are LOTS of different heat treating methods (google "heat-treating knives"), but the quick and easy way is to heat to red-hot and plunge into a bucket of used oil (keep the lid handy in case of flare-ups, though I've never had one). Do this a couple of times. This makes the blade very hard, but too brittle; it'll break. Then heat it in an oven to about 350 for 1 to 2 hours, and air-cool (if you don't want to use an oven, use the torch until the steel is a straw color, but it's harder to maintain an even temp this way). Do this a couple of times. If it's a good sized blade, after it's cooled you can heat the back or spine to a dark blue color with a torch, that will make it flexible enough to avoid breaking without taking the hardness from the edge. If you're going to use rivets or screws for the handle, heat the tang to blue also, that will make it easy to drill the holes (same if you're going to thread the end of the tang for a screw-on cap). It's a toss-up, it's more work overall, but the shaping is much easier. Heavy grinding work on hardened steel can build up enough heat to take the temper out anyway, so I think it's easier overall to anneal, grind, and then re-temper. NOTE to real bladesmiths - I know this is very simplified, and there are lots of different ways (and theories) of heat-treating. This will get the job done pretty easily for casual knife-making.

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