• Mike Romo
    1
    I hear the phrase quite often. Usually in terms of “your geometry is great/all wrong” or “to make a good (insert type of knife) you have to get the right geometry.

    What makes good geometry? I know itks different for different types of blades, but can you guys discuss it in a more technical way? The word geometry implies specific angles, distances, etc. i’m a pretty nerdy guy, that’s why I’m asking for a more technical amswer.
  • Josh Hiett
    8
    I am in NO WAY AN EXPERT but I’m pretty nerdy and technical and I’d like to take a stab at this question. I think ultimately one needs to understand what the knife will be used for and the trade offs for making said knife thinner or thicker. Thick edged knives can handle a lot more abuse but arent as nice to use as thinner ground stuff. Take chopping up an onion for example, my wood splitting axe while sharp would not be good for that task. On the other hand my paper thin rc65 nakiri would not be good for the wood splitting task. I guess as a maker it’s instict now how I grind things for how they will be used. And I would say a maker should have/get experience with the how and why of edge geometry through personal testing of their work.
  • Chop Knives
    57
    ☝ What he said.
  • Mike Romo
    1
    Thanks for the replies. I’d very much like be a podcast fly in the wall and hear you guys just discuss the intricacies.
  • Josh Hiett
    8
    And if you’re looking for specific numbers mine are as follows, for my chef knives which I normalize the crap out of like six cycles pre heartbeat the edge is flat ground to .040” at the edge. Which is crazy thin but with all my thermal cycling I DO NOT EXPERIENCE WARPS! After heat treat my blades are Rockwell 62 tested. I test every one I make. I even test my tester:) then I belt grind down to .008” with 100 grit. Then I flat grind some more on a disk at 180 grit, the edge is now .005 or .006” at this point I’ll feather in the edge on the disk grinder so that I wind up with a slight convex edge then hit the edge on a buffer with green chrome.
  • Smith Knifeworks
    43
    Josh gave a good explanation. If you want to see it in person, find Nick Wheeler's youtube channel, get a beer or whatever you're into and binge watch until you cant take it any more. He is a VERY high level knife maker with the ability to explain and physically show what he's doing in extreme detail. He discusses the procedure Josh mentioned with convexing the edge on the disk grinder. Like Josh, I take my knives to about .005" on the grinder and then put an edge on them at about 15 degrees. I don't convex to a zero grind, but I'd like to try some day whenever I get around to it. This makes them super super thin right behind the cutting edge. It takes a good bit of feel and finess to mash a piece of heat treated steel against a zinging ceramic belt at that level of thinness and not blow the heat treat. I grind with no gloves. You'll burn your hands as the heat wicks through the edge of the knife. That's how I know it's time to dunk. Your skin will get painful before you get to a temperature that is going to draw back the heat treat or blow it completely.


    You can generally tell whats going on behind the edge by feel if you know what you're feeling for. If you handle a lot of japanese kitchen knives you'll start to notice that a great deal of them are actually hollow ground. It's hard to tell if you don't know, but it's there. That's a result of using very large radius grinding wheels as opposed to belt grinders. It has the benefit of allowing you to get the knife very thin behind the edge without having to flat grind way up the spine. There's a lot to this shit. I love learning about the intricacies and idiosyncrasies. Fuad Accawi (Foo-add A-cow-ee, according to him. I asked him to teach me to pronounce it correctly haha) (@fuadaccawi on IG) is another wealth of knowledge regarding heat treat, blade geometry and overall knife mastery. Check his IG feed for him absolutely abusing the dogshit out of a knife, that is ground pretty thin, with zero damage. Steel, when treated properly, is an incredible material. Absolutely mind blowing stuff. Kevin Cashen is also a GREAT resource for heat treat information. It all plays together. You have to heat treat to the way you intend to grind it, or vice versa. The grind and HT have to sync up . A knife with a .005" edge at 50 rockwell is just gonna be an edge rolling turd.

    Happy reasearching!



    Caveat: Knowing this stuff has nothing to do with being able to physically produce the result. I'm proof of that. Grinding a knife that thin, keeping it straight, getting the tip down to nearly invisible. That shit is difficult. I'm still trying to get to where I can do it with some degree of consistency.
  • Mike Romo
    1


    Thanks guys. I have watched a lot of Nick and am always up for some Cashen HT knowledge. That guy is a Jedi. I’d never hesrd of Fuad, so I’ll be following him now.

    I appreciate the candor and frankness and I can definitely identify with the idea of knowing and trying to do for sure.
  • Josh Hiett
    8
    Another important tip that I think a lot of people might overlook is slowing down your grinder. I have all my grinders on frequency drives that I can slow down to a crawl. Post heat treat it’s important not to burn things and slowing my grinders down makes it almost impossible to burn. And sharp belts.
  • Mike Romo
    1
    I’m waiting on my new motor, vfd, and small wheel attachment from AMKoncepts to arrive.
  • Josh Hiett
    8
    you’re going to love the frequency drive thing! It really makes grinding on sensitive materials foolproof.
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