Edge Geometry 101 (What Makes a Good Knife?)
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- Опубліковано 29 бер 2021
- What separates a knife from all other tools is its shape. We generally categorize the discussion of shapes as geometry which is why the term comes up a lot for high performance cutlery.
The only thing that separates a knife from an axe or a metal bar is its geometry so it should be no surprise that geometry is by far the most important factor in knife performance. A thinner angle and thickness behind the edge, BTE, are key for a slicey knife. But not all knives are meant to be keen slicers and are purposely made thicker for heavy duty bushcraft work. So all knives need geometry matched to the task and the steel being used.
I discuss edge angle vs. thickness BTE and assert that edge angle is a more important factor that can overcome edge geometry shortfalls assuming the steel can support the lower angle.
This doesn't get talked about enough. Too many people just talk about slicey knives, but don't talk about end use. I'm a carpenter and mostly do farm maintenance these days. I edc two knives, a fixed blade beater usually an izula, and a dragonfly in k390 for cutting open feed bags or opening packages. Wish I could get an izula in cruwear though
It’s all about the end use and user! Cruwear izula would be sick!
Knives like the Izula still have plenty of potential. I reground mine, removing the coating, thinning the bevel and edge geometry. It's extremely "slicey" now.
I use it for food prep often do to it's amazing performance, and ease of cleaning, since there's no handle scales or folding mechanisms to mess with.
Great video, and topic man. I've started making my own knives, and I'm experimenting with different bevels and edge thickness for different knives, steels, and uses.
With a regrind I bet the izula really comes into it's own! I've stripped the coating off my Esee 6 so I should go ahead with the izula too. Did you force a patina on it after you reground?
@@EngineersPerspective701 Cool! I let the patina on mine form naturally from the food prep I was doing. For a while there it had a cool blueish color after cutting up a bunch of pork.
I think I show what it looks like now, on a video I made about customizing an ESEE Junglas.
Another awesome video!!! So educational. I think another important thing to mention- and please let me know your thoughts on this, because I might be missing something -is that even if the edge angle and BTE thickness is more important than blade stock thickness, having a thinner blade stock thickness means the BTE thickness will stay thinner much longer after many sharpenings. It will be easier to sharpen for longer since you aren’t having to fight against very thick blade stock. Obviously, the blade stock thickness has to match the activity (cutting boxes vs batoning) like you said. So yes, when you have a brand new knife, the qualities you mentioned are most important, but practically speaking, the thinnest possible blade stock thickness (for the given task) will allow those qualities to shine for the long term. You can get a regrind of course, but most people won’t do that, and often thumb studs make regrinding impossible.
I think you’re right on the money! As thin a spine as possible to maximize blade life without a regrind and decrease wedging in certain materials.
@@EngineersPerspective701 Nice! Thanks for that!
You forgot hollow ground vs flat ground. A good thin hollow ground holds a longer distance thinnes behind the edge and out cuts the flat grind of the spyderco in deeper cuts like processing cardboard
Very good point. There can sometimes be confusion with hollow grinds because an edge can still have poor cutting geometry despite the grind. But a good hollow grind can be awesome and really extend the sharpenings a knife can take
Interesting. I heard Murray Carter say that most blades are sold with way too thick of a body so the number one thing to improve the cutting is to thin the blade out, that even a great sharp edge won't cut well if the body of the blade isn't thin enough. Outdoors55 on the other hand demonstrated square edges cutting things just fine as long as the body of the blade was thin enough. Which made me think that the body thickness is the most important thing to a blade. On the other hand I've seen many Japanese knife sharpened with another angle behind the edge and some sharpeners creating that second angle just to thin out a way too thick of a body/spine into a reasonable one and then finishing with the actual edge once there's that cutting performance thickness behind it. That way you don't have to remove the whole blade's height of material even though you create a geometry with more performance. I wasn't too sure of my kitchen knife's metal since it was pretty cheap, so I opt to try out creating a second angle instead of making the whole tall blade very thin, just to see if I can improve the performance with that geometry without compromising the whole blade (I'd think it bent really easily if the whole blade was thin enough even if it could handle the edge without chipping).
Thanks a lot, great video
appreciate the comment!
One correction. K390 is actually tougher than 1095. 1095 is actually quite a brittle steel. Steels like aebl, 52100, or 3v are where you should really be looking for high toughness.
There is more that goes into that K390 and 1095 comparison than a blanket statement but yes it can be.
You mentioned some premier steel choices for toughness too
Great vid. Knifers should know this.
Absolutely
You said you got your Manix reground. Where can I have this done? Great video!
I had mine done by Carter Cutlery but folders were out of his norm. Just shoot him an email and see if he’d be interested in whatever folder you want done. He’s all for any fixed blades though!
@@EngineersPerspective701 Awesome! I’ll definitely check him out!
I love my essay makes a great EDC night especially out of s35
The S35VN do look awesome
hey i had a question about "bite" and finishes, in regarding to steels. how do i know what grit to finish my knives to insure i have the most bite?
You just have to learn through trial and error! First it comes down to your preferences. But generally a higher carbide volume steel will keep it's bite better than a lower carbide volume steel but there are a lot of variables. Poor skill can ruin the aggression of any edge and high levels of skill can make most fresh edges have bite.
As a starting place. My personal preferences are usually fall within 700-3000grit range depending on steel and stones. I'd say most people find a balance around the 1K mark.
I have a video on polished edges on S35VN and LC200N that might be interesting as well.
Great video. I really hope this channel gets more popular. I've watched a few of them now (I can't remember if I've commented before) I just wanted to say you do a great job with this.
One small thing, and this is totally me being a stickler, and I get that this isn't what the video is really about. But idk if I agree with the 1095 being tougher than k390. They're actually pretty similar. And at a given hardness, k390 is pretty likely to be tougher than 1095. Though maybe at those exact HRC numbers the toughness could lean towards 1095s favor, it isn't going to be by much. Again. I know me saying this part is missing what you were getting at. And I totally agree with everything else said here.
I really appreciate the comment!
I think that’s a good discussion point right there! I wouldn’t be surprised if there is an overlap in the impact toughness of the two considering that there are a lot of poor 1095 heat treats out there. Probably still safe to say 1095 has the higher potential toughness but in terms of the knives that we get in our hands it may not be the case!
@@EngineersPerspective701 it's hard to say exactly of course, and it very much will vary. Mostly I have the numbers on 10v to compare rather than k390, but k390 is advertised by bohler to be slightly tougher than 10v, with a similar carbide volume.
But one thing that will vary for sure is whether they are getting to a given hardness with the k390 using a lower austenizing temp+cryo+lower tempering range, or a higher austenizing temp+tempering in the secondary hardening range. The latter will reduce toughness for a given hardness. So that's a variable.
But if we are looking at 1095 at 62 hrc, and k390 at 62 HRC. There is a good bet that the k390 is going to be tougher at that hardness. When looking at 57 or so hrc 1095 vs k390 at 65 Hrc then we will see 1095 coming out in the lead for higher toughness.
And of course 1095 can certainly be effected by hting. I would suspect mainly through Austenizing too high, or for too long, bad quenchant choice, or not understanding tempered martensite enbrittlement. Especially for makers that think that hrc is the only thing that correlates to toughness. They may be tempted to temper too high, actually hurting both the aspects of the steel. Or if they're forming plate martensite with too high of a austenizing temp (which is pretty easy with 1095), or too long of a soak. It's going to seriously reduce toughness, and that will likely be compounded, if they choose to temper it in the range where tme occurs.
I always love looking into these things and comparing stuff like this, so don't take this as me saying 1095 isn't a great steel, or anything like that. I do however find the pm steels in the a11 category to just be super ideal for knife making, unless you want corrosion resistance. Or to spend 100+ usd for a single 12x2x.200ish inch bar.
Hey Justin, can I have your thoughts on going 15 degrees per side on an M4 bugout?
I'd do it. Maybe creep down to it over a few sharpenings to see how the edge holds up and how wide the bevel gets. My guess is that 15dps will be good for it. My M4 PM2 starts to roll around 13-14dps in my own use.
If someone could get Spiderco and ZT to have a Chinese baby, I'd have "my" brand and officially convert into an edc bro. Till then, everything sucks or is at least compromised and it's all vastly over priced for what it is.
It's definitely nice to have a "my" brand. Spyderco is that for me