In another instructable I recommended these instructions
and then realized I'd never followed them completely. On doing so I have come to the conclusion that they're as usefull as I thought and would continue to recommend them as a simple way to heat treat hardened steel.
Step 1: Know What You Need Before You Need It.
Stuff you need:
- about 12 fire bricks (they're usually kinda yellow)
DO NOT USE ANY OTHER TYPE OF BRICKS!
- charcoal, get a big bag use the extra for a barbeque
- lighter fluid, it just makes things easier
- an old file, don't use a new one they're usually just some
crappy soft metal covered by a harder one
- a coarse metal file, a grinder will help speed things along
- a cheap hair dryer, you need something to force air into
the "oven" (be careful if you borrow this, I've killed at
least one for sure) you'll need to find a way to secure this
in front of the oven
- a pipe long enough to reach front to back of the oven, 1/2"
steel is best but I used an old aluminum tent pole and it's
lasted through several heatings
- a pair of long pliers or tongs to handle the metal while
- a small sledgehammer, just in case
- sandpaper, at least 80 and 100, the higher you go the better
- a breadpan, or other suitible metal container
- oil to put in the breadpan, I used 30 weight motor oil but
I've read that olive oil works rather well
- some peices of hardwood for the handles, I had some walnut
from an ice strom a few years ago. hickory, maple, oak, etc.
- epoxy for the handles, preferably the slow set type. I've used
gorilla glue and it worked but epoxy's by far superior
- Acetone (a.k.a. fingernail polish remover) you don't need much
- a saw to shape the handles, wood rasps help if you've got them
- an oven, or whatever you can consistantly heat to 450degrees
F. for an hour
- a knife, chisle, or gouge to cut grooves in the handles
- a finish for the handles, I used linseed oil
- a shaprening stone -not completely necessairy
read through the steps carefully, I probablly left something out. Sorry this list is so random I wrote stuff as I remembered it.
Step 2: Start a Fire
Again let me stress the importance of using bricks specifically made and tempored for use with fire. Other brick types are porous and often contain air pockets, which when heated cause the brick to explode, sending hot brick fragments, burning coals, and your red hot peice of metal flying in all directions.
Make the bottom with four bricks, use two for each side laid edge down on the bottom bricks. use one more for the back, same as the sides. The top will be put on after the fire is started, lay the remaining three bricks on the sides, make sure to leave a gap of about 1/2" at the back of the oven. The pipe goes in the bottom of the oven centered and about an inch from the back, this helps evenly distribute the airflow.
Once you have the charcoal burning, make sure the coals at the front are burning well or the fire won't heat evenly, go ahead and put the top bricks in place and turn on the blowdrier.
Once it gets hot, glowing brightly, put some more charcoal in.
Step 3: Annealing
Now that you've got the oven well heated, take off one or two top bricks (I suggest using thick gloves like those for welding) and put the file into the center of the coals, then add some more charcoal on top of the file.
Watch the file, when it turns bright red turn off the hairdrier and let the fire burn out. Leave the file in the oven until it is cool enough to pick up with your hand. This will take hours.
If the file comes out warped, the oven cooled unevenly but it's an easy fix. Start up another fire just as before. This time when the file turns an even red pluck it out and straighten it with that small sledgehammer I suggested you have. You don't have too much time to do this, if it cools and gets too hard before you get it straight throw it back into the fire and let it get red again. When you're done straightening it, turn off the hairdrier and put the file back into the oven to cool.
Step 4: Transform That Peice of Metal
I used a hand grinder but a bench grinder or hacksaw or even a metal file will work.
Second, if you had to straighten out the file you'll probablly want to get rid of the dimples that were made by the hammer. Use the grinder or file to grind down the surface until you can't tell where the dimples are. Don't worry about removing the grooves from the old file, they are deeper than you'd think and give your knife some character.
After that is done, if it was needed, you'll rough out the cutting area. Twenty to twenty-five degrees is a good angle for the knife edge. You can use the grinder to remove material initally but you should use a coarse metal file to make sure the edge is uniform in angle and flat.
Once the knife edge is roughed out, though it may be quite sharp now, sand the whole thing. Start with a coarse grit like 60 or 80 and work up to at least 150 for a smooth looking tool. You could go all the way up to 600grit if you wanted to use it as a mirror, but that's up to you.
Step 5: Hardening
Heat the oven as before and watch the knife. It will go through stages of dark red colors and then become a bright cherry red. When it reaches this take it quickly and dip it in back first, so the last part to go in is the knife edge. Dip it in and out of the oil about ten times and then leave it in the oil until cool enough to handle.
Make sure the oil is close to the oven so you don't loose any heat in the transfer.
After it cools clean it and sand it back to a bright finish. Once sanded wipe it down and clean it with acetone.
Step 6: Tempering
The easiest way to do this is with a conventional oven.
Set the oven at 425degrees F.
Once up to 425 place the knife in the center of the oven, cutting edge up. This can be easily done by using some wire (a wire coat hanger works well) wrapped around the ends and formed into hooks at the other to hang from the oven rack.
Leave the knife in the oven at 425 for an hour and fifteen minutes. Then turn the oven off but leave the knife in for another thrity minutes. After that take it out and let it air cool somewhere.
The cutting area after this heating should be a yellowish straw color.
Once tempered finish the knife by sharpening it on a stone. I got mine for about $15 from a hardware store.
Step 7: Handles
Cut four small slabs the length you want your handles and half the thickness. Use a knife, chisel, or gouge to make a groove in each peice. A trick I found usefull is to cut the groove in one slap half the thickness of the file and so it is a good fit. Then hold the two peices together and pour sawdust down into the groove. place this on your workbench and carefully lift off the peice with the groove. outline the sawdust with a pencil and check to make sure both peices are the same, then just cut out where you marked.
Once the grooves are finished, epoxy the handles to the knife. Clean the ends with acetone again before you glue them. As you can see in the pictures I used gorilla glue for this project. It really doesn't work well for this, but it does work. Actually one handle didn't set well and I ended up using epoxy to reattach it. So do yourself a favor and go to the hardware store and get epoxy specifically for tool handles.
Once the handles are on and the epoxy is completely set shape the handles with a knife, a wood rasp is also good for this process. Watch out for the knife, it's sharp. Once you get the handles shaped sand them and then finish them. I would suggest using tung oil or linseed oil instead of polyethylene, but that's just a personal preferance.
Remember to oil you knife occasoinally to prevent rust.