fillet Knife

[RingingAnvil]

I have found a couple of boxes of old planer blades and due to the slight thickness and width i thought they would make a great series of fillet knives for the entire world. Does anyone know what kind of steel they might be (i put their birthday at 1958) and how to treat them? Perhaps they wouldn't make good blades at all.

[bigfootnampa]

I've no idea what steel they might be but likely one that will make blades with decent cutting qualities. You might find them a tad on the smallish side for filet knives but they should make some nice carving knives and you might get some smallish filet knives from them. They should make decent hook knives or hoof knives.

[ThomasPowers]

Planer blades are often alloys of extreme hardness and NOT FLEXIBLE.

Think about getting some *large* (as in 6" wide) bandsaw blades used for cutting trees into lumber for material that is both flexible and capable of taking a good edge.

[BIGGUNDOCTOR]

My friend's neighbor was a custom bladesmith, I believe his name was Bob Howell. He made one regular knife, and it was a fillet knife which he sold to commercial fishermen. He use Ats 34 stainless for his blades. He took one that he had finished put the tip against the table top, then pushed the handle down until the blade was forming a 90 degree vee, Very flexible, and yet quite hard with good edge holding qualities.

By planer blades I take it that you are talking about a large power planer, not block/hand planes. Most planer blades I have seen are made of High Speed Steel, and would not make a good fillet knife. It may be worth your while to find out what kind of planer that they fit, and sell them. Take that money, and buy some known alloy to make fillet knives;Ats34, 1095 spring steel, etc.

[RingingAnvil]

Thanks for the all the help and advice everyone.

[Steve Sells]

Thanks for the all the help and advice everyone.

you will find even more information if you read in our blade smithing section.

[thingmaker3]

Here we go again...

"Flexible" means "thin." And that's all it means. An annealed peice of given size takes the same force as an as-quenched piece of same size when it comes to bending. Do NOT take my word for this - go out to your shop and TRY IT.

Sure, some steels have higher strength than others and will take a set (or snap off) with less force per unit cross section. But you can't "heat treat for flexibility." You have to design for it!

[reefera4m]

Here we go again...

"Flexible" means "thin." And that's all it means. An annealed peice of given size takes the same force as an as-quenched piece of same size when it comes to bending. Do NOT take my word for this - go out to your shop and TRY IT.

Sure, some steels have higher strength than others and will take a set (or snap off) with less force per unit cross section. But you can't "heat treat for flexibility." You have to design for it!

I'm trying to understand your 'you can't heat treat for flexiblility' statment. While I agree that the 'design' (as in blade geometry) is a significant factor (as is the steel you choose), I also know that heat treating can also affect flexibililty. If I were to take a leaf spring of 5160, 'flexible' in the beginning then forge and shape it to a common hunting knife shape then improperly heat treat it, it would end up either too soft and flexible (or just soft and bendable) or too hard and brittle. If I heat treat it properly the blade will have some 'flex' to it and yet be quite tough. When adding the 'edge quenching' aspect of heat treating, you harden the edge more that the spine with the intent of having an edge that will retain its sharpness while the softer spine will be more flexible and not as brittle. I consider the proper combination of annealing, normalizing, quenching and tempering to all be under the umbrella of 'heat treating'. The opposite of 'you can't heat treat for flexibility' would be you can "heat treat for brittleness'. Forget to temper and see how 'inflexible' the blade can be - just drop it on a concrete floor.

[Robert Mayo]

Here we go again...

"Flexible" means "thin." And that's all it means. An annealed peice of given size takes the same force as an as-quenched piece of same size when it comes to bending. Do NOT take my word for this - go out to your shop and TRY IT.

Sure, some steels have higher strength than others and will take a set (or snap off) with less force per unit cross section. But you can't "heat treat for flexibility." You have to design for it!

Finaly someone understands ground thin and proper heat treat makes flexible without breaking.

Thankyou Bob

[son_of_bluegrass]

I'm trying to understand your 'you can't heat treat for flexiblility' statment.

I think (and I could be wrong), this a question of semantics. One way to define flexibility is simply the ability to be bent. From one stand-point, heat treating has nothing to do with flexibility so narrowly defined, the flexibility merely comes from the alloy and shape. The amount of force required to put some level of bend in the blade is the same regardless of heat treat.
A looser definition of flexibility includes the ability to return to the prior shape. This is resilience. Using this definition, heat treat does have an effect as the heat treat helps determine when the metal takes a permanent bend or breaks.

ron

[thingmaker3]

If I were to take a leaf spring of 5160, 'flexible' in the beginning then forge and shape it to a common hunting knife shape then improperly heat treat it, it would end up either too soft and flexible

No, it would not. You would have the wrong elastic limit, but you would not have changed the Young's modulus. It would still take the same force to bend the knife by a given ammount prior to exceeding that elastic limit. It just takes a set more easily, which is NOT the same thing.

Don't take my word for it... TRY IT.

I think (and I could be wrong), this a question of semantics.

Yes. Most knifemakers use the wrong semantics and confusion reigns supreme. I encourage everyone here to learn what these words actually mean.

A looser definition of flexibility includes the ability to return to the prior shape.

A piece of steel returns to shape when we do not exceede the elastic limit. And yes, heat treatment definately changes the elastic limit of a piece of steel.

But heat treatment does NOT change the Young's modulus aka modulus of elasticity. Nor does heat-treating change the modulus of rigidity.

The modulus of rigidity, by the way, is proportional to the third power of thickness. If a knife B is 1.25x as thick as knife A, we need almost twice as much force to bend it the same ammount. That 1.95x force goes into 1.25x the area, though.



And HARDER steel has a HIGHER elastic limit. Again - don't take my word for it, go out to your shop and experiment!!!!

[Dan C]

Bumping this thread as I was recently asked by a regular customer if I could make a fillet knife for him.  It would be a gift to his uncle who skippers an ocean charter boat so I felt if I was going to put the time & effort into one it should be made from something that's rust resistant and holds it's edge.  Online research points so far to either ATS34 or CPM154.  Am I leaving out any other type of steels that I should consider?  And am I right to be excluding high carbon steel because of the user's environment?

 

Up to this point all of my knives have been forged from old files, coil spring or mower blades, so my heat treating experience and equipment is limited to a coal/charcoal forge, water or oil quenchant and then tempering either in the oven, stove or forge.  Unless anyone knows otherwise, from what I've read this means I would have to send out any blades to be HT'd and that it makes sense to have multiple blades HT'd at the same time.  I'm assuming a project like this is mostly stock removal, grinding and the handle.

 

For the knife's profile I was planning on borrowing one of my dad's fillet knives and find out what type of profile would be best suited for his uncle's type work.

[Steve Sells]

440C is forgeable, rust resistant, and holds a good edge.

[Dan C]

Thanks Steve.  For HT'ing 440C can you follow a similar process as 1095 which I could do myself with the equipment mentioned above, quenching in warm oil and tempering in a kitchen oven for an R/C of 57 or 58?  Looking at this it would seem so. 

 

http://www.admiralsteel.com/reference/sstltech.html

[ThomasPowers]

Do it up right and get the recipient involved in designing it to suit himself!  Far better to get a custom blade made to your specification than to get a surprise blade that might not suit you.

[Dan C]

Do it up right and get the recipient involved in designing it to suit himself!  Far better to get a custom blade made to your specification than to get a surprise blade that might not suit you.

Excellent suggestion!

[Steve Sells]

Thanks Steve.  For HT'ing 440C can you follow a similar process as 1095 which I could do myself with the equipment mentioned above, quenching in warm oil and tempering in a kitchen oven for an R/C of 57 or 58?  Looking at this it would seem so. 

 

http://www.admiralsteel.com/reference/sstltech.html

 

 after a lIght oil quench, wait for it to cool to air temp, Then do a sub zero quench.   I do not mean placing in the home freezer, that is useless.   many SS need this to force transition of the retianed austinite, as I mentioned in the HT stickys.   If you dont have a bottle of liquid nitrogen laying around, then just get a gallon of acetone, and a large bucket.  Crush the dry ice and place in the bucket, then ad the acetone,  (Never ad dry ice to the acetone, its likes to explode that way) insert the hardened blade into the slush for about 30 seconds, then remove and allow to reach air temp again, then temper in oven at 350F or so.

 

this will reach about -170F  We must use gloves, long sleeves and face protection, and I have to warn that you must use tongs DO NOT TOUCH THE METAL. you wont like it.

[Dan C]

Thank you again, and I like the warnings about things going boom and not touching the metal.  Testing it with your tongue like a popsicle is apparently a bad idea.  I found additional explanations of the steps in the threads below.

 

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You didn't mention a preheat or heat soak prior to hardening though.  Would you normalize 2x, heat to non-magnetic then do the oil quench followed by the subzero quench?

[Steve Sells]

The preheat and soaks are in the paperwork for the steel you are using.  I only talked about after the hardening.  I cant remember them all,  so I dont even try too.   I have them  in my notebook, and I only did 440C once.

[Rich Hale]

Ats 34, 154 cpm and 440C are air quenched steels. 440C can also be quenched in warm oil. All of these steels will do fine for a filet  knife. however if you research how to heat treat them you will find a rather narrow heat range they need before quench.

Not likely you will do that in a home forge. i send all of mine out to professionals..the whole process when they begin takes 24 hours.

 

That includes two cryo quench cycles and if I remember correctly they are two hours long each.  

Did someone mention 1095?

[Dan C]

I mentioned 1095 because that's what I've worked with for most of the knives I've made, but because the person who'd receive the knife works on a saltwater fishing boat, I thought (maybe incorrectly) that it should be made from something more rust resistant.  I did wonder if 1095 finished to a high enough polish would provide it with enough rust resistance in that environment if properly maintained.  I imagine that is what was done prior to stainless being available and seem to recall mention of that in the forum.

 

I'm also seeing this as an opportunity to expand what I can work with.  Some people (including my wife) prefer to always use SS in their kitchen.  Steve & Rich thank you for confirming what I was starting to see that ats34, 154cpm & 440c would need to be sent out for HT'ing, I don't have the equipment to maintain a heat range like that, but knowing that the 440c is forgeable gives me ideas. 

[Steve Sells]

remember read the melt sheet and follow the guidlines abour forging temps.  too high and its cottage cheese, too low and spiderwebs.