False Edge - What is it?

B

blaughn

Joined
Nov 17, 2005
Messages
22
I am a newbie and have read everything I can get my hands on on knife making. I now know enough to know I don't know nearly enough.

I went to a automotive spring shop and picked up a discarded coil spring and several lengths of new leaf spring stock cut-offs. I forged a blade out of the coil spring but could not get it to harden. I even tried a water quench and could easily cut the metal with a file.

The next blade is out of the leaf-spring stock. It is harder but when I try the brass rod edge deflection test, it flexes but when I look at the edge under magnification, it is still slightly deviated at the test spot.

I am using 160 degree Automatic Transmission fluid as a quench. I am guessing the steel is 5160 but realize this may not be the case.

I realize there are too many variables for anyone to diagnose my problem via this forum. I am curious about the false edge. I am gathering that the false edge is the one in place during hardening and tempering and this is ground away to get to the true edge? How much do you need to grind away and how is this best accomplished? Will a file remove material from the false edge?
 
A false edge usually refers to a beveled section of blade that is not sharpened, for example the clip section on the top/front of a bowie or fighter.

How did you judge critical temperature of your blades prior to quench?
 
When I reach non-magnetic - I heat for several minutes more and then edge quench - point first for 2 seconds, then the full edge for 10 seconds, then rock point to full edge until color is gone.
 
some car springs are made from plain carbon steels like 1095, meaning they'll have a narrower window to get below the nose of the transformation curve during quench.

take a piece of your steel, heat to critical, and immediately stick the whole thing in water and move until cooled. then check it with your file or whack it with a hammer. should be real hard and brittle.

what is your heat source? "several minutes more" in a hot forge could be too long.
 
I am using the Goddard "one-brick forge" and a propane hand torch. It is slow heating to critical but luckly, I am working with a small blade, 3.5" long, and it is intended to be an experiment - not a work of art.

Thanks for your interest and help. I will try a piece as you have suggested and post again.
 
Fitzo, I've come across mention of a sharpened false edge and they still called it a false edge !!!
 
I'd think "sharpened false edge" would qualify as an "oxymoron"! :)
 
Okay, I did that. Heated it to non-magnetic and just a bit more - water quenched. The new file will mark it but not take any material. It "skitters" across the surface. A solid hammer blow rebounds off the face of the material.
 
Sounds llike it's about as hard as it should be. I should have said put the steel partly in a vise and smack it....good chance it'll break dead hard. A new, quality file should have hardness of 63...just a very small "bite" and skate.

You're on the right track....try it on the whole blade next. After that you can deal with things like edge quenches.

BTW, forgot to say "welcome to BF" before...:)
 
Your'e welcome!

The probability of cracking with a blade is much higher using water. Personally, I'd perhaps try the oil again but heat it more in the 120F range. Regardless, I'd do a full quench, and take a quick check with the file and if hard, have the oven ready for tempering. Start low, as you can always creep up on it after you have an inital "snap temper" to take some stress out post-quench.

Part of the problem with edge quenching is that the heat from the spine will creep back into the blade quickly, interfering with the quench. My personal advice would be to creep up on the technique if you are working alone without a mentor. Get a blade full-hardened and properly tempered to pass the brass rod and cutting first. There's plenty of time for the fancier stuff like differential hardening after the basics. Just my opinion... take it with a grain of salt.
 
I will give it a try and let you know how it goes. You realize, of course, you are probably aiding and abedding an addiction.......:)
 
I'll check back here to see your results.

There are worse bad habits, I promise you. :D

What's yer first name and whereabouts are you, if you don't mind telling me.
 
Well, I got the hardness I was looking for, thanks to your advice. It would appear I have reasonable steel to work with.

Now to put a finish on the blade.

Mike, thanks for your help.

The name is Bruce Laughton. I'm a retired manufacturing guy living in Minneapolis (actually one of the tropical southern suburbs of Minneapolis.)

Your input actually allowed me to think through the hardening process. As a rookie, I tried to accomplish an edge quench by putting 3/8" deep oil in a small pan. I think you are right, the heat from the spine of the knife worked against hardening the edge. This was increased by the fact that the small volume of the oil was quickly heated up. When I increased the volume, the results changed dramatically.

Thanks again!
 
blaughn said:
I tried to accomplish an edge quench by putting 3/8" deep oil in a small pan. I think you are right, the heat from the spine of the knife worked against hardening the edge. This was increased by the fact that the small volume of the oil was quickly heated up. When I increased the volume, the results changed dramatically.
Thanks again!
Click to expand...
:thumbup: I'm with mike..



I will add when Mike said
narrower window to get below the nose of the transformation curve during quench

in layman's terms:D
get it out of the heat and dunk it fast , you don't have much time..
welcome aboard Bruce :)
 
Bruce, it is my pleasure to be able to have helped!:)

Some bladesmiths agitate their quench tanks to improve convection cooling.

Good luck with the finishing!
 
Great forum - BTW, friendly and helpful - informed and tested sources rather than opinion. A rare and refreshing combination.

I will post a picture of my first effort as long as I can invoke the "No Chortling" rule. :)
 
You'll find that there is no chortling at first knives and naught but encouragement. :) Though there is the occasional surprise at a wonderful "first knife", most of us had much humbler beginnings.............

And you're quite right, there are many knowledgable, helpful people on this forum. I have learned a great deal here.
 
Welcome to the forum Bruce. We are always happy to have a new steel pounder, come on board. Fred<-Bethel Ridge Forge-> :D
 
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