Customizing knife questions on grinding and tempering/heat treat-

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mmtmatrix

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May 15, 2000
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Hey guys lets say that I have a knife that I want to modify by making it double edged. This is going to require removing a fair amount of steel, is there any way that I can do this without destroying the heat treat and having to retreat and temper it? Or am I going to have to anneal it, grind it and then re heat treat it? I would love to hear any information on the subject, I have a project in mind, and would love to do it, but me knowledge and skill on the subject are minimal, so everything is appreciated. Also, if I was to ask a maker to do this for me, what type of response would I get? Will most makers not do this because its a production knife/should I not both with the question?

Thanks,
mmtmatrix
 
If you had one of those grindstones that turns through a tub of water and were very careful that might work... The French used to have these GIANT grind wheels in one of their knifeworks that were like 14 feet in diameter and turned in a pool of water. The bladesmiths would lay on boards spanning the groove these wheels ran in(yikes!!!) and would look down over the edge and grind the knives on the wheels. I bet it did one hell of a job at stock removal!
 
You can grind it without ruining the temper, if you are careful.

when I'm stuck with this kind of situation, I try to keep the knife wet and a bare hand on the blade above the grinder. If the blade is dry, your hand is warm or you notice even a slight change of color on the blade, dunk it in water.
 
Thanks for the help guys, I really appreciate it. I knew that if I did it carefully that it could be done, but am I going to get good results on a high quality knife? Is it going to be effective and efficient?

Let me say this, I have done a very very small amount of grinding (if you can call it that), but it has been with a small hand held mini grinder with a 4in. wheel, is that going to mess it up and make it look bad? Any tips?

Thanks,
mmtmatrix
 
Well if I understand correctly,you are wanting to take a fixed blade single edged knife and grind the spine to make it double edged. If this is the case the spine shouldn't be as hard as the cutting edge is right now, it should be softer to give the blade strength.So you will have to harden the new cutting edge to make it perform properly. And in order to do that you will most likely have to reheat treat the whole blade.(both cutting edges.)So I would take the handle off,grind the blade the way I want it, then heat treat, then you'll have to sand
the whole blade to remove any carbon scale from heat treating and to bring the blade to the desired finish.Replace the handle and your done.But before I would do all that I would be sure I knew what type steel the blade was made from. If I understand correctly,if not ignore everything I've said.

Hope this helps
Bill :)
 
It's actually a folder in 154CM... (and I would probably disassemble and clamp it to my work area)

Am I crazy, or is this plausible/feasible?
mmtmatrix
 
it's only an opinion, but I don't like double edged folders,

so yes I think you're nuts,

but don't let that stop you. and please take pictures and post them when you compleet the project:D
 
Like Bill said, when the blade was originally heat treated the thicker spine would have retained heat longer and would be softer than the thin cutting edge. If you grind down the spine to a new cutting edge it will be softer than the original cutting edge and should be re heat treated.

The answer to your next question is NO it can not be heat treated at home.
 
Is the spine going to have a softer inside even though it would be a rather thin blade?

Eric, I completely agree with you, I also don't particularly like double edged folders, but this is for something special, and it is/I will make the exception.

Thanks,
mmtmatrix
 
I'm no expert, and I don't make folders (yet) but the cutting edge up about 1/3 to 1/2 the blade should be the only part that is hardened. I would think on a folder that the metal would be to thin to grind a good double edge and still have much of a knife left, I would want to start with thicker stock, grind in my double tapers leaving the blade thick in the middle like a dagger,but this is just my opinion.

Good luck:)
Bill
 
Anyone else want to help/share advice or shed some light onto this?

Thanks for all the help,
mmtmatrix
 
Just go ahead and grind it man. Even unhardened steel could be made sharp. It just wouldn't hold it. I doubt that a production knife was so carefully hardened that the spine will be much softer than the edge. Before you start though you must ask yourself: If I screw it up completely, will I really care that much? If the answer is 'yes' you shouldn't do this.
 
just go for it

you said you were going to take it apart, so what the heck, if you screw up the temper or it's not hard enough, send it out to be rehardended.

as for the 4 inch mini grinder, I use a die grinder to grind the inside of carving gouges It takes a little practice, but it's doable

it would probobly be easier if you could find a way to anchor the grinder and move the blade rather than the other way round.

get a scrap of steel and get the feel of what you are doing

you can get a good hollow grind on a half inch stone if you watch the sparks. You should see a line of sparks all the way across the stone. If the sparks are on one corner you are digging that corner in. Go back and forth with a steady motion. let the stone ride in the hollow it makes.

do not push

rest the blade against the stone.(very soft touch) let the stone do the cutting. go to the thread where I posted pictures.("I figured out how to use the scanner") the 2 hollow ground blades were done on a 6 inch bench grinder out of joiner steel. It takes me an hour to grind one with out burning it. I'd say allow about three hours for grinding.

clamp the ricasso in vise-grips to give you a handle for grinding.

I hope this is helpfull Eric
 
I ground the partial serrations off of a BM 812s and gave the knife a recurve instead. This involved putting an edge on a part of the knife that didn't have one before. I did most of the work on a Dremel and the rest with a Lansky extra coarse diamond hone. Worked perfectly. And I didn't know what I was doing either. The best thing I did was practice first on a POS knife. I learned enough from doing this to get the real one right. Keep a cup of water right there and dunk the blade before it dries and you shouldn't have any problems with adverse reactions from the heat. Go for it.
 
154CM is an air hardening steel, so hardening basically involves heating it through a specific temperature range from 0 to its critical temp and holding for the specified time, then letting it air cool. Because of that, the thicker part of the blade, will cool more slowly than the cutting edge and end up softer. But I think you'll find the difference to be negligable for what your doing.Since the blade is so small, heat can easily wick its way thoughout the blade through whichever part is cooling fastest. The difference in hardness is no where near that of a diferentially tempered blade.
And even if its a point or 2 lower on the RC scale, your not going to do a whole lot of cutting with the back edge anyhow. It won't need to hold an edge as well as the primary cuting edge.

You should be able to do it as long as your careful. Did you say that you were going to do it with a hand held angle grinder though? I don't know if thats a good idea. You could pull off a chisel ground edge if you were very careful. But you won't have near the control offered by a beltsander/grinder, or a benchgrinder. You'll have to really really watch the heat too. Angle grinders run super fast and will cause the blade to heat up alot faster. Make sure you've got a fine grit wheel and something secure the blade really well.
 
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