5160 fillet knife question

Evan Miner

Evan Miner

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Joined
Nov 24, 2011
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152
k to start if been asked by a guy at work to make him a fillet knife. in payment for some hard wood and an anvil he found me. the blade needs to be 10 to 11in. the steel i make knives with is 5160. i was wondering what would be the best way to temper the spine to give me the proper flex with a straight return iv done a few test but none truly successful on the return to straight theres always some permanent tweak that stays after the pressure is released. iv tried heat treating it with a coat of furnace cement coating the spine to give me the differentially harding then tempering at 400 degrees for 2 1hr cycles. and iv tryed drawing the spine with a propane torch. is there a better way to do this that any one has done
 
I've always been told that the flex has nothing to do with the HT process and everything to do with the thickness. Thinner blades flex more.
 
ii understand the thinner the more flex my last test blade was at .065in at the top of the spine is there a point of being it thin? what should the thickness im should aim for
 
NJJ said:
I've always been told that the flex has nothing to do with the HT process and everything to do with the thickness. Thinner blades flex more.
Click to expand...

Agreed. I've asked similar questions before. I was told that O-1 ( the steel I was curious about) could be HT to 60 and still be flexible. The hardness had nothing to do with flexibility. If I remember correctly, the forum member who replied told me to look up the "Elastic Modulus".
 
so pretty much the same on thickness. k so the question i need to answer then is why does to stay curved after the pressure is released
 
hardness will dictate when the blade takes a set or brakes but not the amout of flex up to that point. if it takes a set you have exceeded the yeild of the steel for the hardness i think maybe the steel is not as hard as you are thinking it is

aafter rereading your post the spine is soft and therefor holdig the set if fully hardened and tempered you will not get the set in the blade (but you might have a ful on fail of the blade when it goes ) your blade as it stands with soft back will in failure crack the edge but then stay together due to the soft spine
 
thanks again i just looked up elastic modulus on a quick note i might be over tempering the spine is why so little pressure is not allowing my blade to fully return ill do more reading on it tonight and go from there
 
jsut as a side note i have a cpm154 SS blade that i can flex 90 degrees and have it spring right back (hardened to 62rc )
 
Don't bother trying to differentially harden the blade or draw back the spine more than the edge.

Just make sure you have good grain refinement, good hardening, a nice thin blade and draw the whole blade to your hardness specs.
 
69 Knives has it exactly right. Fillet knives should not be differentially hardened or tempered, that's for choppers etc. 5160 is a great steel for fillet knives- we use it all the time for that application and it is very hard to make one fail even at HRC 61.5 in the blade cross section (VERY thin flat grind) of a fillet knife. Remember that cross section is essentially what determines flexibility and likelihood of cracking and blade failure. Make sure your spine is lightly rounded or eased to remove the 90 degree stress risers and it should flex all day long.
 
For perhaps a better understanding of thickness vs. flexibility; I work in the electroplating industry and sometimes people bring us items that have been plated, poorly and cheaply, maybe, if they're lucky 0.001" worth of nickel. Recently I had some plated items come in that were so poorly plated I peeled off the whole plated surface of basically what was an 8" round aluminum pipe, 10" long, the nickel plating was so thin I could wrap it around a 1/8" rod.

Now, we use copper wire to hang things for plating and the copper wire will typically develop up to 0.025" worth of nickel and it is impossible to bend; you can try and it will simply break.
 
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