Norm, there's lots of ways to skin a cat, but here's how I go about making a file into a full tang (chiruwa) knife via stock removal;
- Blade is shaped by "cold grinding", i.e., go slow and careful to avoid overheating the steel. I generally rest my thumb on the blade just opposite of the section being ground, so I can feel whatever heat's being generated, and dip the blade in a bucket of water if it starts getting too warm. By taking care not to overheat the steel, you keep the file at it's full hardness of around 64RC. From there you can temper it down later in a regular kitchen oven, but if you burn the hardness out by overheating the steel while grinding, you'll need access to a forge to reharden it.
- Once the blade and handle are ground to pretty much final shape, I draw the hardness from the handle portion so that it can be drilled for rivets later. I do this by wrapping the blade in a wet rag, leaving the handle exposed, and then using a propane torch to heat the handle sufficiently to remove the hardness. Don't worry if you aren't familiar with reading the oxidation color changes at various temps. Just go right on past blue until you get an even shade of silvery gray. Try not to let the area of the blade/handle juncture go past purple (spring temper), as that area gets a lot of stress, and you don't want it too soft or it may bend and not spring back. Control that by where you place the wet rag wrapping the blade. Once the handle portion has been heated, allow it to slowly air cool, DO NOT QUENCH it, or it won't soften right, and you'll burn up your drill bits. Keep the wet rag on the blade, and with the butt of the handle pointing up, leave it alone to let it cool.
- Now it's time to temper the blade itself down a level of hardness/toughness more suitable for a knife. Make sure the blade is clean and shiny, so you can readily detect color changes in the steel, then put it in the oven. Any (decent) cook will tell you that no two ovens are exactly the same, so I won't talk about temperature settings, other than to say 325 degrees is a good starting point. What you want to do is very gradually increase the temperature until you arrive at the oxidation color change you want. Just crank it up 15-20 degrees at a time, and check it in 10-15 minutes to see if anything's happening. I know it sounds tedious, but once you get a feel for it, you can whittle the process down a bit. The key is to heat slowly, and afterwards let the blade cool slowly. All I do once I hit the color I want, is to turn off the oven, open the door and leave it open, and leave the blade right there until it's cool enough I can handle it with my bare hands.
Okay, I've been talking about colors, what color do you want to see? First, you'll see a pale yellow color, with a little more heat that yellow will take on a light brownish tint (the color of a good ale, like Bass). You can generally stop right there for a general purpose knife, but for a knife that's going to see heavy use and occasional abuse, you'll want to go even darker until you get a light bronze color. You can even turn a file into a nice, springy, throwing knife, by heating it up to a light purple, but that would make it too soft for a good cutting tool. Dark straw yellow, that light brownish tint (remember the ale) is probably all around your best bet.
- Handle? Here's how to cheat. Make sure everything's clean, then epoxy and clamp your rough cut handle slabs to the tang. When the epoxy has set up, clean up the edges of the handle slabs to match the contours of the tang, leaving the slab faces perfectly flat for now. Mark the locations of your rivets/pins, chunk the thing on a drill press, and whoosh, drill right through the whole shebang, i.e. both slabs and the tang in one lick. Result, perfectly aligned rivet/pin holes. Now you can finish shaping your handle like you want it, and then put in your rivets/pins. I generally use 1/8" brass rod, epoxied and peened with a hammer and anvil. Then I file the peened heads down flat, and sand the whole assembly smooth. Apply the finish of your choice, make yourself a sheath, and go cut stuff with your new knife. :thumbup:
Sarge
