fillet knives

[redneckrampage]

im getting ready to cut out a fillet knife or two...seems ive been using one of them more than hunting knives, but talking to my dad he said fillets need tripple draw back qeunching in the heat treating process to get them good and flexible again, although i prefer a bit of a stiffer fillet what would some of you reccomend for heat treating on a fillet, the steel is either 1090 or 1072 .072 thick spring steel...i forgot to mark it after a coworker ripped it to strips in the laser at my old job

thanks for any help

steve

[redneckrampage]

anyone got any input

[chiger]

Hey Steve,

Sounds like pop knows something about forging steel.  He's right about it needing to be flexible.  But I don't think they need to be as bendy as those store bought things.  He's also right about it being brittle if you just take it to critical and quenching it.  However there are a couple different ways to skin that cat.  

You can do as you dad says and treat it like spring makers and do a draw back quench.  Or you can do a differential quench, either by doing an edge quench or a clay quench.  I like edge quench.

Or you can do it by doing one quench and and a higher end of the temper cycle to get the whole blade to about 38-40 Rc and then use a torch or forge if you can to heat just the edge to critical and just re quench the edge. Then re cycle it at a lower temper temp to get the edge back hard.  Kind of a modified draw back.  

I've even heard of guys doing a regular quench and then using a torch to heat the spine and tang to soften them while the edge is in water. Then doing a regular temper cycle.  

As I said, a lot of ways to skin that cat.  But I'd say the spin does need a little flexibility to it or someone will snap it pushing too hard against the cutting board.  GRRRRR!

Oh, forgot to mention.  All 10** series steels are what is know as shallow hardening tool steels.  It's not going to get really flexible no matter how you treat it.  You'll be depending on the thinness of the blade to let it bend and being just hard enough to keep it from staying bent without breaking.  It's kind of a delicate balance with shallow hardening steels.  But you can do it.

[redneckrampage]

ummm chigger, pardon my ignorance of being a rookie could ya explain a bit more the heat treat methods you talked about, as i only have one blade under my belt and that one ended up about a half inch shorter than started, and yea my ol man has carved a blade or so in his time, hopefully my entrance into knife making can get him back into it as hes made some beauties..

[chiger]

Hey Steve,

Ain't no need for pardons.  I ain't no dang expert either.  I'll just do a walk through and you can ignore the stuff you already know.  Hows that?

Ok, I guess what I would do in your situation is the easiest thing and see if it preforms as you want.  And I'm assuming you're using a homemade charcol forge given what you wrote about the wifes hair dryer.  You know she's gonna catch ya dude.  And you'll need at least a propane torch.  This should soften the spine to about 40-45 Rc.  

The easiest would be to heat the blade to critical...the lit says 1475-1550, but just heat it till the grind at the top is none magnetic.  I like to use one of those extendable magnets on a car antenna lookin' things.  Fire hot.  Me sissy.  

Anyway, as soon as the grind of the blade, don't worry about the spine, just when the top of the grind reaches critical you quench it tip first, edge down in a light oil heated to at least 130, but absolutely not a degree over 180.  I'd prefer 160.  

I'd also recommend using a vegetable or peanut oil if you temper in your wifes kitchen or the smell of oak will be the best thing her hair could smell like.  ;~0

As soon as it's quenched, off to the temper oven.    Don't spend time admiring your work, wipe off the oil as you walk and have it in the oven as quick as you can.  You should already have the oven preheated to 375-400 before you quench. I like to use a dish with sand in it to set the blade edge first vertically.  Keeps the temp more constant.  

It should stay in for 1 1/2-2 hours.  That's more than a blade that thin needs, but it won't hurt.  Then turn off the oven and let the whole thing cool to room temp together.  Just so you can tell you've done something after the next step, clamp the tang and grab the tip.  Carefully give it a little tug and see how much it flexes.  Should be pretty stiff so don't snap it.  Just feel how stiff it is.  

Now, take some 220 grit and brighten the blade and tang back up so you can see the color change.  Use a propane or and oxy/acetylene torch to start heating the tang and spine of the blade.  Just do a small section at a time and then dunk it in a bucket of water.  Take your time.  

Your are trying to get it to a brownish-purple color, near purple (around 500F) heat as you can without letting the heat creep down to the first 1/2 inch of the edge.  If you see the blue start creeping to close to the edge, plunge it into a bucket of water.  

You don't have to start over every time.  Once it's purple once, it's done.  But do NOT let that first 1/2 inch get any hotter than that slight copper color it was when it came out of the oven!  If you do, you'll have to start over.  Tempering won't fix it.

Continue that until you've got the whole thing except that half inch along the edge.  Oh, and I wouldn't worry about the first inch or two at the tip either.  When you're finished, put it back in the oven for another quench cycle at 400 degrees for 1 1/2 or 2 hours.  Let it cool to room temp in the oven again and give 'er a test run.  ;~)  Should be a lot more flexible than the first time.

I've never done this method to a whole knife before, but I have done it to toughen tangs before I developed another method.  And I've read recently about other guys that have done whole knives and even swords using this method and swear by it.  

If you have any trouble, it doesn't work as well as you'd like or just want to try one of the methods that only the sickening ping of breaking steel can teach, let me know.  I'll be glad to write another long and confusing explanation that may not work either.  ;~)

Seriously, good luck.  Hope it works for you.

[redneckrampage]

thanks for the rookie wording chiger, when you put it in sand do you put it in verticle or horizantley in the oven, and with panfish i seem to prefer a bit of a stiffer knife for peeling the sides off of the gills

[KHALVERSON]

horizontal
cutting edge in the sand
i too prefer a short and stiff fillet knife
for those dinner plate size gills

[chiger]

Sorry rampage, been tied up.

Mr. Halverson is right.  That's what I do.  

And heck, I have a chefs knife I made that I used on a mess of slab crappie and large mouth the other night.  I prefer wide, thin and fairly stiff blade to fillet with too.

[redneckrampage]

hey chiger, i put a pic up in my newest project post, could ya give me suggestions on what youd do for heat treating, i may try the torch method but will have to stop about 2.5-2.75 inches from the tip as it drops pretty thin after that

thanks for any help