Tempering a knife

[Bootsctm]

What is the proper way to temper a knife? Am wanting to take some old files and make them into knifes. When I reshape them using a grinder it would cause the knife to loose it's temper correct? So what steps would I need to do to temper the knife after I have it in its final shape?

 

[LRB]

If you are going to grind it, you can temper it first, as is, then grind while constantly cooling in water, but if you see heat color come into the edge, it's over. You'll have to re-heat treat it by re-hardening and tempering. Not to sound picky, but there is a difference in tempering and hardening steel. Tempering is done after the blade is hardened, by re-heating at a much lower temperature in order to soften the steel a little, making it less brittle than full hard. Files, good files, can make excellent knives, but I'm not sure you wouldn't be better off starting with an easier steel to work with. 1084 steel is relatively cheap, and very beginner friendly in heat treating with less than professional equipment and methods. If you insist on using files, use only Nicholson or Simonds to be sure of good quality steel. The steel you decide to go with will determine the way of heat treating the blade. There are a few extra steps, although simple, with the 1084, but would be easier in the long run than working down a file. You decide, and I'll help you as best I can.

 

[ohio ramrod]

During the fur trade era knifes and files were shipped west in about equal amounts. By the Gold Rush era mostly files were shipped west, knifes were then made from worn out files. You need to first anneal (soften ) the file this can easily be done by simply building a bed of red hot wooden coals, laying the files in the coals, racking the coals over the files and then letting the coals burn out and the files slowly cool. Then when you have you knifes finished, reheat to a light cherry red, quench in light oil. Then reheat to between 550 and 750 degrees depending on desired temper. Allow to air cool slowly. Most electric ovens will go to 500 to 550 degrees, lead melts at about 740 degrees depending on purity. So a melted lead bath is often used to temper knifes or springs. :idunno:

 

[LRB]

Sorry Ohio, but to use an overused expression, "with all due respect", that is not really, truly, quite the best advice.
It is not best, or necessary to anneal a file in that manner. Bring it up bright red/red-orange and let it cool will allow it to be drilled or filed. Bring it up to a very dull red half a dozen times seems be even better. Colors are seen differently by different folks. One shade of red, or heat color, beyond non-magnetic is the target heat for the quench for a hypereutectic carbon steel, and should be close to 1475°, give or take a bit. Light oil is correct, but it needs to be heated to about 125°, and canola oil would be the best as far as cheap and easy to get appropriate oils. Once into the quench, the blade should be moved fore and aft, but never sideways. Point down into the quench causes less warp. The temper for a file blade can be as high as 500°, but not much more, as it is possible to cause the steel to become brittle in the 600° range. This problem begins in the mid to low 400°'s range, so it is best to not push the temp too far over that. Two one hour tempers at 450° should be very sufficient, and quench in water after each temper heat. Lead melts at 625°, not 740°, which in fact is a good temper heat for springs. A little much for most knife purposes. Again, sorry to correct you, but your info really needed a wee bit of adjustment.

 

[ohio ramrod]

You are obviously better informed than I am at heat treating. But my methods do work for me. I use a lead bath for springs, and some knifes and a kitchen oven for most knifes . (I have a separate oven in the shop so swmbo doesn't make me sleep in the shop) :idunno:

 

[Rifleman1776]

Here is how I did it. (sub-titled: How Not to Harden a Knife)
One year, at Friendship, The Atlanta Cutlery was selling many blades they had purchased in England. They came from a factory that (reportedly) had been locked up some 200-250 years earlier. Some had been heat treated, some not. I bought several and took them home. One was a large blade that I really liked. Knowing nothing, but going on someones advice, I hung one with a thread over a can of oil then heated it to as bright a orange/red as I could get with a propane torch. When it wouldn't attract a magnet anymore, I cut the thread and let drop into the oil. When it cooled a bit I took it out with pliers the turned around....Uh-Oh!.... :shocked2: ....I accidentially hit it against my vise and it shattered into a dozen pieces like glass. Bye-bye new antique blade.

 

[Billnpatti]

Oh manure!!! That's got to hurt. I have made a few knives from scratch but not enough to be an expert on the process. I have used files, car springs and industrial hacksaw blades to make knives. When I made a knife from a file, I just heated it up cherry red and put it in a pile of wood ashes to cool over night. I did the same to the pieces of car spring to soften them to where I could work on them. The hack saw blades, I just ground out the knife blade shape, used my torch and wood ashes to soften the tang and then had to take the blade to the shop at work where they had drill bits hard enough to drill the holes for the handle rivets. When I tempered the file blades and spring blades, I just heated them up to a dark red and tossed them into a pan of old motor oil. After cleaning them, I would put them in the kitchen oven for a couple hours at 450 and then just turn off the oven and let the blade cool slowly. I would then take the blade and do the final sharpening and put on the handle. When I ground out the hacksaw blades, I worked slowly so as not to overheat the metal. I would leave the teeth on the back of the blade to use when cutting through bone. They worked great but were brittle so you could not horse them around when cutting. Still, they worked fine and I got several years out of my favorite hacksaw blade knife until I loaned it to a friend to dress out his deer. He was one of those folks who could dent an anvil with a rubber hammer. He brought my knife back to me in two pieces and said he would replace it. I told him not to bother, it was just an old junk knife that I had made. I turned away and wiped away a tear.

Nope, didn't know what I was doing and had no metallurgical knowledge beyond what I learned in high school shop class but.........I managed to have fun making a few knives. I never turned out a knife that would make a real knife maker worry about the competition. But they worked and the hacksaw blade knives held an edge extremely well even if they were fragile.

 

[Bootsctm]

Thanks everyone for the input!