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Heat Treating Filet Knife

Discussion in 'Heat Treating' started by Joelsund, Oct 10, 2020.

  1. Joelsund

    Joelsund New Member

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    Working on my first filet knife. Does anyone have any recommendations on heat treating them? I’m using 1/16th AEBL so it should be able to flex quite well. I’m thinking I should temper it quite soft to about 58 so it doesn’t snap. AEBL is already pretty tough even at a 60 so I’m thinking I should definitely be fine at 58. It’ll be mainly used for pickerel so won’t be cutting big bones. Any input would be greatly appreciated.
     
  2. Scott Kozub

    Scott Kozub Member

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    I've done a couple at 61 they were quite flexible. Almost got to 90 degrees before snapping. If you want more flex grind it thinner.

    I don't like AEBL any less than 60. The edge starts to roll in the 50s.

    My suggestion is 62 and grind thin. You can always temper back a little more if you want before mounting the handle.
     
  3. Joelsund

    Joelsund New Member

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    Good idea, I’ll try 62. Thank you
     
  4. dancom

    dancom Dust Maker Best Shop Tool

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    I heat treat at 1060°C, air quench, temper at 200°C for 2 x 2 hours. Grind after heat treatment. The thinner you grind the better it'll flex, but there is such a thing as too much flex also. My last two were from 3/32" AEB-L, but the blades were ground distal taper until I felt a good firm flex. I don't know of an exact way to to measure this. I just press it against the bench and feel the bounce.
    [​IMG]

    Dan
     
    Last edited: Oct 11, 2020
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  5. FORGE

    FORGE Maker of the Year Best Knife

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    Last edited: Oct 11, 2020
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  6. dancom

    dancom Dust Maker Best Shop Tool

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    This is true. Of course, you'll know if you flex it and it stays bent, you've blown the heat treat.

    Keep grinding until it behaves the way you want.

    Dan
     
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  7. Joelsund

    Joelsund New Member

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    Thanks everyone! I have read that article from Larrin before. I have a few pieces of aebl so maybe I’ll try a few different things. My assumption was that the softer I go the further it can go without deforming or snapping.
     
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  8. Griff

    Griff Active Member

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    I’ll go on record (again:D) to say that fillet knives scare the :poop out of me lol!
     
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  9. dancom

    dancom Dust Maker Best Shop Tool

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    You've probably heard that AEB-L warps pretty easily. A 12" piece of 1/16" stock can go kind of bendy on you. I know it's not everyone's cup of tea, but I would recommend grinding the bevels after heat treatment. Also, make sure it's as straight as you can get it before going into hardening.
     
    Last edited: Oct 12, 2020
  10. Joelsund

    Joelsund New Member

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    Yeah, a little worried about that. The blade portion is about 7.5“ including the handle it’s about 12“. My quench plates are only 8 inches long so hopefully if it warps it’s on the handle and I can straighten it out. And yes I’m planning to grind after heat treat, since it’s already 1/16 it should take too long. Do you guys have any ideas of how to grind it without having it flex? I don’t have a grinding jig so I was going to try attaching it to a flat bar with a magnet and grind one side at a time
     
  11. dancom

    dancom Dust Maker Best Shop Tool

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    Avoid having to straighten if you can help it. Straightening air hardening steel is a huge pain. We're talking multiple hours of near tempering temps, jigs and so on. I prefer to just hang thin AEB-L from a nail or wire and blow compressed air at it. Plate quench will likely warp unless you can drop the blade precisely between the plates and make the left and right surfaces contact the plates at the same time. I've had limited success with long pieces in plates.

    For grinding, I use the flat platen, pressing the blade into the platen with my thumb, and reducing the pressure as I draw across towards the tip. I use bare thumbs, a fresh 36 grit ceramic belt and a bucket of water. An old dull belt is your worse enemy here as it will want to burn the steel. If your thumb starts burning it means that heat is building up. A burning thumb is fortunately no where close to ruining the temper so you'll be safe with this method. Heat builds up pass after pass, so frequent dunking in the water bucket really helps. Once the edge is down to about 20 thousandths, I move to a 60 grit. Then around 10 to 15 thousandths I'll switch to an X weight 120 for a few passes. Hand sand or conditioning belt from there. Should be in around 10 thousandths before setting the edge at 17°. It will be an impressive slicing tool.

    Dan
     
  12. Joelsund

    Joelsund New Member

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    Thank you for the advice! I’ll skip the plates. I just got some fresh belts in so I’ll definitely use them. cut it out today. Here’s a picture.
     
  13. Scott Kozub

    Scott Kozub Member

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    You have about 10 seconds or so after the plate quench where the steel is very soft and can be straightened but once it hits the liquid nitrogen or dry ice it bends again.

    I was considering not using AEBL anymore due to the warping. Then I made a peening hammer out of an old hammer and a carbide masonry bit and now it just takes a few minutes to get them perfectly straight. No bend and no snapping. Only cost a few bucks
     
  14. Joelsund

    Joelsund New Member

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    when do you hammer it? in the 10 seconds after the quench?
     
  15. Scott Kozub

    Scott Kozub Member

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    Right after the plate quench you can easily bend by hand. Just make sure it's cool enough to touch. I use the hammer technique after the blade has gone through the cryo and tempering. Do not hammer it before tempering! Even if the knife is straight going into the LN it usually comes out bent.

    I just took an old hammer and drilled a hole in the face that would accept a masonry bit. You may need to soften the hammer to drill it. I rounded the bit over as best I could on a ceramic belt (carbide is very tough to grind so your just knocking off the sharp edges). Find the center of the bow and gently tap the cupped side of the knife. The carbide bit should make little dimples in the knife. This spreads the metal and makes it bend the opposite direction. You can be very precise where you want to bend the blade. Once straight, head to the grinder and finish. If you have a sandblaster that can work also. I just find the hammer easier.

    I try to post a you tube video on the next batch I make to show what I'm talking about.
     
  16. Scott Kozub

    Scott Kozub Member

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    Here's a youtube video showing what I'm talking about

     
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  17. dancom

    dancom Dust Maker Best Shop Tool

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    Thanks Scott. That's a really cool idea.

    Dan
     
  18. Joelsund

    Joelsund New Member

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    hmm, cool thanks.
     
  19. FORGE

    FORGE Maker of the Year Best Knife

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    That is the last thing I would use on a thin hot blade that just came out of the furnace or salt pot. All he is doing is putting little stress risers in the steel which causes it to bend. An old knife maker in Montana once told me you only want to believe about 10 % of the crap you see and hear on the internet .... his estimate may have been a little low, maybe 15 % is believable.
    I once took a completely hardened and finished filleting knife blade and sand blasted it. The blade must have moved 3 inches off of the centre line. Then try and blast the other side and get in to come back to centre..... impossible to achieve.
    Anyway just my thought on the process.
    Happy hammering.
     
  20. dancom

    dancom Dust Maker Best Shop Tool

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    Wow, is this one of the 15% or one of the 85%?

    Was that old guy Ed? I didn't think he was that old. :roflmao
     

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