tempering

[Medic85]

Just wondering how you fellas go about tempering your old file blades.

[gudspelr]

Since no one's answered, I'll give it a go. I think some clarification may be in order, or at least some more info from you to best help you.

Are you asking how to best temper a knife that was ground out of a file? This assumes you ground a still hard file without over heating it which would result in a softer spot on the blade.

Is it ground all the way to finished thickness and only needs to be sharpened? Tempering means you want to soften the blade-what are you shooting for in a finished knife/what will it be used for? I think many guys who've made knives by grinding a file out just left it the same hardness and just used it from there.

In a nutshell, tempering a blade is a combination of time and temperature. That's why you'll see guys temper various steel blades for 2 cycles of say, 375 or 400 degrees instead of one cycle at a much higher temperature. As a rule of thumb, think of higher temps bringing your blade hardness further down. So, if you begin at a lower temperature of 350 and run 2, 2 hour cycles, test it after. If the blade is still too hard, pop it back in the oven to temper at a slightly higher temp. This really brief explanation is how many makers go through the tempering process with "mystery" steels to obtain a good working blade.

I hope that answers your question at least a little. If you could provide some more info, you might be able to get some more help.


Jeremy

[D.Ellis]

I am assuming you mean Heat Treat, not just Temper.
The trouble with old files for knife blades is trying to determine the proper HT procedure......which varies depending on the steel type the file was made from. Some of them were also made from mild steel with a surface(case hardening) treatment done to make the teeth hard.
But, assuming you have a file made from high carbon steel.......which is fairly likely, and you'd like to make a knife from it. Here is the basic procedure.


1-Shape the blade either by forging or grinding........if you choose to grind, or file, the blade to shape, you will find it very helpful to anneal the file first. Heating to dull red and cooling slowly will do a half rate redneck job of annealing most simple steels........for a full anneal, it is more complex.


2- Harden the blade. This is accomplished by heating the blade as evenly as possible to the transformation temperature. You can judge this fairly close by using a magnet and testing the steel with it as it heats up. When the magnet quits sticking, go just a shade brighter and then quench(dunk the blade) in warmed up oil or water. Try the oil first as water(or brine) can cause the blade to crack. Some steels require a faster cooling quench than most commonly available oils will do, in which case you will need to use water or salt water(brine). I use canola oil, it's non toxic and has a fairly fast quench speed.


3- assuming you now have a hard blade, it is too brittle for use. Now you need to TEMPER the blade to a useful hardness........ideally hard enough to hold a good edge and soft enough to not be brittle. The hardness that is ideal depends greatly on the edge geometry and also on the steel type. But the basic idea is to heat the blade up to anywhere from 350 to 500 degrees f and let cool to room temperature. Repeat the temper twice and each temper heat should be at least 2 hours. To nail the correct hardness, try the lower heat first, then sharpen and test the blade. If the edge chips easily, temper again at maybe 25* hotter and try again. Repeat until the blade performs to your expectations.


This is the very condensed and simplified version.
Best of luck,
Darcy    

[Medic85]

I really appreciate it guys.  Just starting out with all of this and I had some old files laying around figured I'd start there.  Thanks again.

[tomsm44]

I'm not going to comment on HT procedures as I'm still learning myself, but here's my two cents.  If you want a really good knife, I would start out with a known steel and try the files once I got more experience.  Lin Rhea convinced me to do that a couple of years back when I asked a similar question.  Once I realized how cheap good steel is, I never thought about using files, saw blades, etc again.  Midwest knife supply has 1 foot lengths of 1084 steel for around $5-$10 depending on width and thickness.  It is simple to heat treat, makes a great knife, and since you know what it is going in, it's easy to find exact HT instructions for that specific steel.   Not to say you can't get a great knife from a file, it'll just be harder to nail the HT on it which means you emay not get the full potential of the steel.  Good luck with whatever you do.

Matt Toms

[D.Ellis]

I agree with Matt about using known steel, but there is a certain appeal to recycling used steel, kinda goes with the traditional territory. Whatever floats your boat if you are building them for fun. The worst recycled high carbon steel blade, with a half ways decent heat treat, will still outperform the stuff guys were cutting with in the bronze age      :D  
Darcy