Tempering A File Knife

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Bighaze51

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Dec 26, 2012
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Okay, so I have another hair rained idea. I'm going to make another knife from a file. However! I want to do it without annealing and heat treating. I'm going to cold grind it with a side grinder and water. I know it takes longer to do it this way but I've made a carving knife the same way and it's been a fantastic little knife. I want to make a fixed blade about 7 inches total. My question is about the tempering process. Since it will already be in a hardened state ( roughly 65-66 RC?) what temp and how long should I "cook" to bring it to about 62 RC? Or should I leave it at the full hardness? I won't be doing any prying or anything, I want pure edge retention for slicing. I don't know I'm just plotting. Any ideas?
 
I did this at 550 in my oven, the resulting blade was pretty hard and took a while to grind. It takes a decent edge though.
 
If you temper at 400 F for an hour that should drop the hardness down a bit. It should be in the HRc 60 range but we are guessing a little as the composition of the steel is not known for sure. You can assume it is similar to 1095 and probably be OK. There used to be a sticky on shop talk just dedicated to making a file knife.
If you decide to temper in your oven at home, get an oven thermometer as it will be more accurate than the ovens dial. Get a pan of sand and bring it to temperature in the oven. Place the file in the sand and temper that way. The sand as a heat sink will help maintain the temperature around the file at a more consistent level..
 
BoT nailed it :thumbup:

When in doubt temper at a lower temperature first, say 350F, and grind/sharpen the edge and do some test cutting on tough materials. If the blade is too hard/chippy, temper it again 50 degrees higher to bring the hardness down a bit more.

If you temper too high to begin with (500F is pretty high for a simple steel) the steel will be softer than you want and you'll have to anneal and re-HT it from scratch. Tempering should be done for a minimum of an hour, and preferably twice (cool to room temperature between cycles).
 
Cool deal. Thanks for your help guys. I didn't really even think about doing multiple temperatures to get it right. That's why I come here. The wealth of information :)
 
Okay, it's been a while but I've finally gotten ado to this project. I cleaned out my "knife drawer" last night and found this Nicholson file I had stashed for this project. I decide to draw out this shape very loosely based on my Izula. It's mostly the handle shape of the izula because it's comfortable in my hand but I prefer more of the drop point and less of the belly. The length is goin to be about 6-1/4 inches. My plan is to slowly bring the blade on my 1x30 belt sander. I have time but I don't have a forge. Plus, at this point I don't want to hassle with heat treating. This will be my lunch break project over the next week or too. My plan is to keep it cool and then temper it down in the oven when I'm done. I'm using an old ruler cut in half and tightly bound around the handle to use as a gaurd/stop to get an even line when grinding the blade edge down. I started today and so far so good. I'll post some pictures as I profess but here is the shape I've come up with

 


I forget the time needed but when I used to anneal knife files in the oven I shot for a "straw" (somewhat darker yellowish) to let them bend a bit but still be pretty hard. Polish a bit first to be able to see color.
 
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Dave, thanks for that chart. That's a perfect help to me. I want to run this blade a little harder than most people would but not so hard to be really chippy. This helps big time. Thanks!

So I've started grinding and as expected, it's slow going. I'm using an 80 grit belt right now until I can get to the store and pick up a 40. So far, I'm pleased with the results. I'm using a ruler cut in half and taped to the handle as a stop so my bevel will be even against the handle and it seems to be working. Hopefully I can pick up a few belts tomorrow and get this project really rocking.


 
Dunno how good it is. To me, a file which has gone full blue is pretty soft. Still, yellow or straw seems like a good thing to shoot for. I think I did that at about 400 degrees for 20 min or so. *YMMV*

I used to have the luxury of access to dull knife files of good quality. The profile was mostly already there.

 
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straw should be about 425 to 450, I would run it two or three cycles with cooling to room temp between, 1095 which is Nicholson normal steel would be still chippy ay 400. you want the color (straw) on the edge thinner stuff is going to color first. I have some pics up on the natural hones forums under knives, should you want to see what I make.
 
I forgot to mention it, but your oven temp need to be checked to be sure that 450 is 450 the thermostats vary. I have seen 450 setting go well over 500. you can find a thermometer at most grocery chains to be sure, assume nothing , check everything.
 
kn4wd said:
I forgot to mention it, but your oven temp need to be checked to be sure that 450 is 450 the thermostats vary. I have seen 450 setting go well over 500. you can find a thermometer at most grocery chains to be sure, assume nothing , check everything.
Click to expand...

I have heard that as well. I've got some thermometers laying around so I will be sure to do that.
By the way, what part of SC are you in?
 
Interesting read.

I am in my second childhood.

Back in the beginning, when I started my 39 years journey as a Toolmaker. The master ToolMakers sent us apprentices free, on common grinding wheels to earn our basic skills, to make things with files. One thing learned was not to overheat and destroyed the heat treatment came with the files.

These I made 40+ years ago, still sharp as a razor for their intended "Extreme Hard Use" purpose. They all can shave the cutting edge off my personalized Sebbie with its 58-59 HRC, in the background:

DSCN1964_zpsd5ce5590.jpg


:)
 
Those are slick, I like it. My first file knife will get scary sharp and hold that edge. That's why I've decided to do this project. Right now I'm carrying an Izula everyday and I'm just not happy with the edge retention on it. This one I'm making is roughly the same size, which i like and will hopefully make me happy with increased edges retention. Plus I'm not really in a place to spend rediculous amounts of money for something better
 
I am very close to Gaffney, at least mailing address. closer to a little spec in the road called Pacolet.
 
It's nice to know there's other people crazy about knives nearby. I'm about 15 minutes outside of lexington.

So here is my progress so far. I picked up some 40 grit belts and they are working nicely. This steel is HARD so I'm definitely going to cook this one in the oven a bit. I've almost got my flat grind done but it still needs a little stock removal before moving to finer grit belts. I cut the ruler guards off to see how I looks and so far I'm happy with the progress. This one is going to be sweet. My buddy has a bunch of walnut scraps he's going to give me for handle scales too. I'm excited

 
I annealed mine first, but after the heat treating, I tempered at 350 for an hour. It was a Nicholson. Came out quite nice.
 
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