1. Harley Boatman

    Harley Boatman

    Jun 21, 2020
    So I finally got my knives back from heat treat and I was cleaning up the bevels on a knife that had been ordered over a month ago. (It took over 3 weeks to get back from heat treat)

    After every pass on the grinder I dunked it in water to keep it cool to the touch, and then on the last pass (before I closed up shop being absolutely furious) I got a rainbow show up towards the tip. I'm assuming I've destroyed the heat treat there and now I don't know what to do other than start over entirely. I suppose I could grind off part of the blade to get rid of it, but 1) I've already sent the customer a picture of the progress when I had just finished grinding the bevels pre-heat treat, so he knows what it's supposed to look like, and 2) He requested a stabbing blade, so grinding it back would significantly detract from the point and make it very un-stabby.

    If you guys have suggestions and/or tips for the future, PLEASE let me know.

  2. seanj

    seanj Gold Member Gold Member

    Mar 1, 2010
    If you could post a photo it might help. I've ground back several tips that got over heated like that. If you follow the same geometry the only thing you should lose would be a bit of length. Talk with your customer about it, Hopefully he will be fine with a knife that's a 1/4 to 1/2 inch shorter than what you originally showed him.
  3. Boggs


    Feb 27, 2007
    There’s a Knifemakers discussion forum where you’d be better served with answers
  4. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    You may have slightly lowered the hardness in the tip, but it isn't likely that you destroyed the knife. It may even be less likely for the tip to snap off in a stabbing event.
    Photos will help.

    Friendly Reminder:
    At your membership level, please don't discuss knife sales. Your question here would be more proper if you just asked about the issue without discussing the fact that the knife is an order and such.
  5. Nathan the Machinist

    Nathan the Machinist KnifeMaker / Machinist / Evil Genius Moderator Knifemaker / Craftsman / Service Provider

    Feb 13, 2007
    I would send it to back to HT for anneal and re-harden. No big deal. I've had plenty of work annealed and re-hardened for various reasons.
  6. AVigil

    AVigil Adam Vigil knifemaker working the grind Platinum Member

    Feb 17, 2009
    Be sure you to use new belts, dull belts will burn metal quickly
  7. scott kozub

    scott kozub Basic Member Basic Member

    Jan 1, 2018
    How thin is it ground? You can put a quick edge on the knife and do a brass rod test to see if it is too soft. If it doesn't spring back you're looking at a retreat or re-profile.

    I read a great tip here to never let the tip pass the first third of the belt. Once the tip gets to the mid point it's easy to apply too much pressure and burn it.
  8. Harley Boatman

    Harley Boatman

    Jun 21, 2020
    I'm not familiar with that test, how does it work?
  9. Natlek


    Jun 9, 2015
    Watch this
  10. scott kozub

    scott kozub Basic Member Basic Member

    Jan 1, 2018
    If your HT is too soft the edge will deflect and stay deflected. If it's too hard it will chip or crack. The great thing as that the works for any steel type to let you know in your a workable range and you can test all along the blade. The thinner the edge the better for this test.

    I had one of my very first knifes come back because it wasn't holding and edge very well. I did a hardness test (didn't have a tester when the knife was made) and I got 58-60 HRC. This was AEB-L I now run my AEB-L knives at 63. I thought that may be ok but sure enough I had spots where the edge wouldn't spring back.
    Last edited: Jul 31, 2020
  11. Harley Boatman

    Harley Boatman

    Jun 21, 2020
    Well you've convinced me to start testing all my knives. I've made a few for friends, none yet for myself, so I haven't been able to really use them and put them to the test in real world applications. I've been weary of sending the knives off not knowing how they'll hold up. Granted, my friends won't get mad if it doesn't hold an edge because they got a free knife :D

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