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Troubleshooting Common Knife Problems

Discussion in 'Heat Treating' started by John Noon, May 27, 2016.

  1. John Noon

    John Noon Well-Known Member

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    Found this article to be very informative, certainly help out us beginners.
    http://www.texasknifemakersguild.com/troubleshooting-common-knifemaking-problems/

    For those who don't like links copy paste below. I know I have managed to complete most of the failures all on my own :rolleyes:

    Troubleshooting Common Knife making Problems
    Here are a few tips for dealing with some of the places where things commonly go wrong.

    Dealing With Warpage
    Sometimes the blade comes out of the quench crooked. It can be straightened hot, above roughly 500 degrees, immediately after the quench. Use welding gloves. Once it’s cool, it can be straightened during the temper cycles. Clamp the blade to a piece of steel that is flat. Use shims if necessary. Run through temper cycles as usual. Sometimes takes a bit of trial and error, but works almost every time. If you want a two-piece knife, go ahead and try and straighten one cold by putting it in a vise or three point jig. High risk of catastrophic failure with cold straightening.
    Edge chipping is an indication that your edge is too brittle, either from poor normalization prior to quench, too high a temperature going into quench, or from being too hard. If the edge is chippy, try tempering 25 degrees higher. May not be able to fix if brittleness is from poor temperature control during the austenizing heat.
    Edge rolling is an indication that your edge is too soft, either from failure to harden or from tempering too hot. There is no easy fix for this one. Re-heat treat.
    Overheating during heat treatment often results in the blade not hardening correctly due to grain growth. The overheated blade can often be rescued by normalizing prior to quench. Overheated blades can be soft or brittle, with large grain.
    Overheating after heat treatment is typically from grinding with too much heat. If the edge turns blue, you’ve over-heated. Overheating after heat treat makes the knife edge too soft. Re-heat treat, and dip the blade in water next time to keep it cool as you grind.
    Tempering too long happens when you forget you have a knife in the oven. As long as the temperature remains steady, there are no ill effects.



    Tempering too hot results in a soft knife. Most of the time two cycles are recommended. Do the first one 25-50 degrees below the second one. If you over-shoot, you have to re-heat treat.
    Knife didn’t harden
    -Not enough carbon in the steel. Is it a known steel, or something you found somewhere?
    -Incorrect heat prior to austenizing. Did you normalize?
    – Wrong austenizing temperature. Do you have temperature control? Try 25 degrees higher. If not, use a magnet or table salt to get closer.
    – Wrong quench for the steel. Not every liquid will harden every steel. Your steel type must match what you quench in. Use a faster quench liquid.
    -Layer of decarburized steel on the outside of your knife due to forging. Grind in a little further and test again.

    Divot in the blade flats, usually about 2” from the plunge lines- This is caused by tipping the blade toward the point, usually because of trying to focus on the plunge. You’re going easy and careful on the plunge, and the other side of the belt digs in. You can’t polish it out. Go back to at least 120 grit and grind it out, keeping the blade moving to avoid any divots.

    Handle material burns or discolors while shaping- Light materials like maple, or hard materials like oak or osage, or oily materials like desert ironwood are the worst. The common causes are a dull belt, or too fine a belt run at too fast a speed. Switch to a coarser belt, a fresh belt, or a slower speed, and use a lighter touch.

    Gaps between the tang and handle are the result of surfaces not being flat. Either the tang isn’t flat, or the scales aren’t flat. Go to a flat platen, disk, or surface plate and smooth everything up.

    Scratches still visible after polish are the result of a poor underlying grind. Go back up to at least 120 grit and polish again. Make sure and get all the previous grit scratches out before you progress to the next grit. If hand sanding, make sure you are switching directions with each grit change, and make sure you have good lighting.

    A dark ring around handle pins is either the result of oversized or out-of-round holes, where the glue fills the gap and shows a ring, or is the result of grinding your pin stock down too quickly so that the heat burns a dark ring in your handle material.

    Uneven plunge cuts are a sign of beginner’s level work, and even plunges are one of the telltale marks of a well made knife. Consider using a file guide. Make sure you scribe a center line on the blade before you grind. Consider grinding your final plunge cuts after heat treatment. Above all, practice! This is one of the most difficult parts to consistently get correct. Perfect plunges are the result of practice and attention to detail, and are never “easy”, even with practice.

    Handle pins or bolsters sticking out further than the surrounding handle material are the result of hand sanding with no backing, or with a soft backing. The sandpaper cuts handle material faster than it cuts pin material. Try a hard metal backing to your sandpaper, and sand from metal to wood, not wood to metal.

    Handles popping loose are typically the result of poor surface preparation. Oil on the tang, including fingerprints, makes the glue not stick. Use acetone or denatured alcohol to clean the tang, and rinse with clean water. Make sure your tang and scales are flat and clean. Don’t squeeze all the glue out of your joint, and use good glue.
     
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  2. Mythtaken

    Mythtaken Staff Member CKM Staff

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    Is there a prize if you've done them all? If so, I WIN!
     
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  3. dancom

    dancom Dust Maker Best Shop Tool

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    Yup that's my list of experiences too.
     
  4. John Noon

    John Noon Well-Known Member

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    Read the list and laughed, could have saved much trouble if I did a little research before starting my first knife. Between shaping a blade or watching videos I would rather be in the shop.
     
  5. SDMay

    SDMay Active Member

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    Thanks for the list. I have yet to encounter most of these but I am very early into the hobby and I am sure that I will run into most of these at one point. I have a hard time going slow when I get in a groove.
     
  6. krash-bang

    krash-bang Active Member

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    I made a lot of those as well and I found some new ones to put on my "to do" list.
     
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  7. Grayzer86

    Grayzer86 Active Member

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    One thing to add to the topic of a knife not hardening is CONDITION of the steel when you get it. Much of the 1084 and many others steels out there now are coming finely spehroidized. This is great for drilling and grinding, but it also means the carbon wont get into proper solution and conversion using normal HT methods. Some of these steels need to get to 1650 or so and be cycled back in basically a normalizing process. the simple heat above non magnetic works AFTER the normalizing, but if done from the as purchased, speroidized state, they wont harden, or will harden more spotty than a dalmatian, with some spots dead soft, and some getting up into the high 40s to 50s possibly. I had a large batch fail, even when done perfectly to spec in a salt bath, and have since determined that this was the issue. Within a one inch circle we found hardness between 34 and 52. For this reason, many are not suggesting 1084 as a beginner steel now, due to the extra steps and control needed. For forging guys this isn't a big deal because the forging heat blows out the speroidized structure, and they will be normalizing anyway. For purely stock removal guys, this adds extra steps and complications. This grain structure info is from Aldo, and most steel originates from him, including the stock from Canadian Knifemaker. It would be nice if this info was added to the steel listing on their website actually. Recently i switched from 1084 to 1095 and 80CRV2 for this reason, because i was having failures with 1084 and couldnt nail down why, until i found this info. For those using steel from Canadian knifemaker, you can call or email New Jersey Steel Baron, and ask about the structure im sure. As for AKS, Chuck has a full list of the steels he sells and which are speroidized and which are not, however i believe his source is different from others.
     
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  8. Mythtaken

    Mythtaken Staff Member CKM Staff

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    Interesting stuff Grayzer. Like everything, steel production can change over time. It's good advice to test your blades from time to time.

    I really like 1084 and haven't noticed any issues with it. However, I've gotten in the habit of a normalizing cycle before heat treating, to alleviate any stress areas or work hardening from drilling or enthusiastic grinding.
     
  9. Grayzer86

    Grayzer86 Active Member

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    I havent had any issues when i do a normalizing with a high starting temp, but had issues when I went straight from grinding to HT. This has been a highly discussed topic on other forums for the past few months so I wanted to make others here aware of it.
     
  10. Slannesh

    Slannesh Active Member

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    Good to know.

    I got into the habit of normalizing right from the get go even though I don't forge mostly because it seemed like the right way to go about it. Takes some extra time sure.... but seems like i've saved myself some headaches by doing so.
     

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