cKc
Selecting the right Geometry
May 30, 2020 12:18AM
Click to enlarge and read

I've made so many knives in so many geometries, and generally i've like them all. generally id say they all have good cutting qualities, but they are not all good for the same thing.

This first image is one i posted to instagram to outline how i see so many knives promoted as being amazingly thin at 0.010" behind the edge at 15-20 dps. but this really doesn't feel that thin to me. as small as it seems, this form of apex edge can still be very prohibitive to good cutting in plastics, woods etc that dont seperate easily.
so this first chart was to show the difference in apex between one in a similar geometry to one of my small micro hikers, and a same knife had it been made from a normal factory at 0,010" with an overlay on the side to show the dramatic difference.



now of course.. thinner is always better.. but sometimes thinner can mean too fragile. for examplea thin stock, high grind if you only have 2 bevels, primary/edge can end up too thin like a foil or super thin chef knife and not as strong as you want. in these cases, the problem i see with just thickening the apex for duability is that you have a knife that looks like it could cut like a laser, but really doesnt
The answer to me is faceting, or convexing.


this image shows 3 different knife profiles and why i personally tend to go for somewhere in the middle of the 2 extremes.
the left section shows the 3 grinds up to the height where a 12dps scandi reaches stock thickness,
then to the right of the text is an apex closeup showing the overlaps up to the point where the FFG would hit its 0.010" BTE, and then far right is the entire edge cross section.

the reason i tend to go for the middle offering, or a convex version of it is to get the best of both worlds. i want the apex stability of the FFG at 15dps, but i only want it for enough to stabilize the apex against rolling.. so no more than 1-3 thousands in height. so this tiny bit may be subtly thicker than the scandi, but many scandi will also bolster the edge with a micro for the same reason. the scandi is liked because its thin apex can really bite in well, as can be seen from its thinness compared to the green FFG.. but the middle ground is even better to me, in that if you target 7dps (which is where a lot of real traditional finnnish knives not being cheap mora's are ground) then you really get the leanest bite into the material with good apex stability.

but the difference between the long 7dps bevel compared to how a FFG is ground is that you can go very thin on the apex, without the steel being too thin behind it. there is a good support structure that is even, the apex is not stronger than the backing which can occur with an obtuse grind on FFG.

that small increase in thickness behind the edge makes the knife a lot stiffer to support the thinner cutting edge. and in the terms of the entire knife, its really not a lot thicker than the FFG..
you end up with better entry, and stronger support.

the trick is fine tuning this and blending it to get the best attributes..



Waht ends up happening is that you can end up with knives that appear thicker and as iff they should cut worse than thinner smaller knives but in most applications will do better just because of the apex geometries.

an interesting knife tester a little different from catra in how it works in that it tests sharpness across the entire edge to see where on a blade wear is occurring the most for profiling use of a knife in industry, and working out how to sharpen a knife for best results, including variable edging.




in general though. i will always take thicker stock with thinner apex, than thinner stock with thicker apex.

but for most utility, i think i prefer real scandi knives, where we are talking about 1.5- 2mm stock for knives and a grind that is no more than 7dps anywhere on the blade except the final few thousands of the edge.

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It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
cKc
Re: Selecting the right Geometry
May 30, 2020 12:22AM
Very Calm approach to explaining things.






----------------------------------------------------------------------
It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen



Edited 1 time(s). Last edit at 05/30/2020 12:25AM by cKc.
Re: Selecting the right Geometry
May 30, 2020 12:56AM
cKc,
Good stuff. I find myself using my performance ground knives more than my abuse/beater knives. It reminds me of this video Cliff made:
[www.youtube.com]




And how using performance ground knives improves your knife skills. I think knife skills and sharpening skills are very important for a knife user, but they seem to fallen out of fashion.

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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cKc
Re: Selecting the right Geometry
May 30, 2020 01:53AM
yep. in most things in life as the skill of the user gets better it allows them to use tools that will be broken by lesser skilled people.. but in turn leads to overall better experience and performance.

in cutting in a kitchen for example.

people are used to dull knives that rip through things. they are used to tossing them in the sink and nothing worse can happen.

give them a sharp knife, they loose a finger because normally its ok to press down on your finger with a kitchen knife.. they cut from thinness not sharpness. they make you cry because they rupture onions instead of slicing them.

but then, they will press with the same pressure, and slam it into the board.. they slam it harder than they expect and apply lateral forces while its stuck in the boards. this leads to it rolling and dulling fast.

they then conclude that the dull knife is better. it doesnt cut their finger off.

but a skilled hand will know how hard to press the knife so that it doesn;t keep slamming into the board. they have control of the blade so that lateral loads are minimized..

its like people that slam their breaks on at every stop sign and every blockage, vs those that use gearing and controlled decelleration to stop the car carefully..

or the difference between easing off the break at that last moment before stopping to orevent that suspension springback that throws you in your seat.

skill matters in all things in life. just depends on how much it matters to people.

the knife world is often kind of like the couch martial arts world that wants to watch and see the UFC, but not really put the time in to get the same results.,. just buy some gear and kit and go to the gym once a month to look the part.

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It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
Re: Selecting the right Geometry
May 31, 2020 03:02PM
cKc,
I was going to make a separate thread, but this topic seems an appropriate place for this idea: Initial sharpness cannot make up for a poor cutting geometry, while a knife with a good cutting geometry can still cut easily, even when dull.

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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cKc
Re: Selecting the right Geometry
May 31, 2020 05:07PM
Yes, in general this seems to be the case.

but of course, there is also the case where sometimes, just sliding the edge over a stone to kill the apex, even with good geometry will struggle such as certain types of woods that you are not tryint to strip wood off with the grain. but geomtry is always a huge factor imo, and so typically if the goal is to get a better knife.. if you really want a better knife, this is only going to be achieved through steels that can retain structural integrity at thinner geometries.

bigger carbides can not get to the thinner geometries, so they are not really capable of winning IMO the knife war. if you can get a fine grain knife with very small carbide size, small grain size etc.. a very pure simple steel, but get it to 70rc and still be tough.. then we are talking about a serious knife taken to a zero grind.

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It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
Re: Selecting the right Geometry
June 03, 2020 11:30AM
Quote
cKc
Yes, in general this seems to be the case.

but of course, there is also the case where sometimes, just sliding the edge over a stone to kill the apex, even with good geometry will struggle such as certain types of woods that you are not tryint to strip wood off with the grain. but geomtry is always a huge factor imo, and so typically if the goal is to get a better knife.. if you really want a better knife, this is only going to be achieved through steels that can retain structural integrity at thinner geometries.

bigger carbides can not get to the thinner geometries, so they are not really capable of winning IMO the knife war. if you can get a fine grain knife with very small carbide size, small grain size etc.. a very pure simple steel, but get it to 70rc and still be tough.. then we are talking about a serious knife taken to a zero grind.

I have something along those lines... Blunt Cut Metalworks made a roughly 4" 1095 blade @ 67 RC. Now the grind has not been fully zeroed but I have taken it at least under 10 DPS... I cannot measure exactly. It performs beautifully, yet resharpens quite well considering the RC being so high. He used to post here, but he posts a lot at Blade Forums. Basically, he experiments with changing HT protocol and using that protocol across a very wide range of steels to test performance. Sadly, his protocols as of late have been targeted more towards the higher carbide stuff as the current protocols are optimized for these steels.
cKc
Re: Selecting the right Geometry
June 03, 2020 11:36AM
do you have any images of that knife?
do you know if it is through hardened to 67 or edge hardened?

if you have calipers it would be nice to see some photos showing the grind at different depths 0.01", 2, 3 etc

I've followed his channel a bit on youtube. seems like some interesting work he is doing.

how extensively have you tested the knife.
do you believe that it backs up his own videos and claims in use?

----------------------------------------------------------------------
It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
Re: Selecting the right Geometry
June 03, 2020 04:07PM
It is through hardened and tested upwards of 67 RC, it is ground relatively thin but I don't know that it's quite on the level of your stuff Kyley. Sadly I do not have calipers... I need to change this though. Whats a good buy on a decent set for these types of uses?

While I have not used the knife extensively, it has done quite well and I do believe it does perform as advertised. He claims that by getting upwards of 63 RC you get much longer edge retention as that is harder than silica and other common debris that blunts edges, much longer being relative to what it is compared to.

I have cut quite a bit of meat going through all manner of very dense connective tissues, it holds the edge quite well through this and it tends to blunt other knives quite easily. Sinew I believe has quite a bit of silica in it by nature. Most of my knife usage for the last few years has been in the kitchen, no time for outdoor stuff lately.

Maybe you can tell something regarding it's grind from these photos, I don't know how telling they will be but who knows. It is 1/8" stock thickness for reference, if I am remembering correctly I think I asked him to sharpen at 12 DPS before he shipped... I think I dropped the angle even more... it's pretty close to zero now in that I can easily scratch the primary if I'm not very careful holding my angle sharpening.

















Edited 1 time(s). Last edit at 06/03/2020 04:09PM by Nothingman.
cKc
Re: Selecting the right Geometry
June 03, 2020 04:50PM
nice. looking at the image from the plunge, and working out cross section based on 1/8 stock it looks like the edge would be 8-10dps excluding any potential micro bevel.

so no chippyness? rolling/

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It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
Re: Selecting the right Geometry
June 03, 2020 05:11PM
I have not experienced either, I even smacked the edge once accidentally into a hard window sill... not sure of the material. It barely showed any damage at all, want to say it just rolled slightly but it was a long time ago... a few years or more.

I do use a micro bevel on it to refine the apex after sharpening to plateau, but I don't really raise the angle much at all to do this so it's probably no more than 12-15 DPS micro. It's one of those knives that I've pretty much decided to keep no matter what, the only thing I don't like is carrying it on a belt the pointy pommel hurts a bit.
cKc
Re: Selecting the right Geometry
June 03, 2020 05:14PM
grind it off grinning smiley

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It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
Re: Selecting the right Geometry
June 03, 2020 05:32PM
Thought about it, I have this thing about leaving stuff like that though... even though it bugs me the maker put it there for a reason so I leave it and just don't carry it much. It definitely serves a purpose, I'm just not operator enough to handle the awesomeness I guess. He called it a fighter/utility when I bought it... it does give the thumb a nice solid resting place held with reverse grip edge facing in. If it were a Busse, I could call it the Skull Crusher Pommel TM... but I don't dare invoke the wrath of Jerry's attorney's ... smileys with beer



Edited 1 time(s). Last edit at 06/03/2020 05:35PM by Nothingman.
Re: Selecting the right Geometry
June 03, 2020 05:34PM
Double post, I need some lunch lol.



Edited 1 time(s). Last edit at 06/03/2020 05:35PM by Nothingman.
cKc
Re: Selecting the right Geometry
June 04, 2020 11:49AM
Quote
Nothingman
I need to change this though. Whats a good buy on a decent set for these types of uses?

Calipers cheap

i ordered a cheap pair. i prefer digital just because its easy to flick from metric to imperial

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It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
Re: Selecting the right Geometry
June 05, 2020 08:11PM
The real question I am left with regarding simple steels at +63 RC, can they be sharpened easily in the field if they are in fact harder than silica? Sand is plentiful where I live, all you have to do is dig in the soil anywhere... you could easily sharpen with this if you must normally just by applying some to a flat piece of wood. Not sure how well this would work at +63 RC, but I do believe I successfully sharpened this 67 RC 1095 on a this inexpensive natural stone I have... can't be 100% though as my memory is foggy.

[knifewear.com]

That stone is interesting finding a knife it works well on, seems well suited to any of the simpler/softer steels. I have not used it extensively yet, but it basically requires lapping with a diamond plate to raise a slurry in order for it to cut and not just glaze immediately. I am not sure if this is a very low grade natural Waterstone, but I suspect it is for this reason perhaps... or maybe it's just there's a a lot of voids and mixes of abrasive layers in it. For anybody looking to experiment though I think it's worth looking at.
cKc
Re: Selecting the right Geometry
June 07, 2020 06:36AM
Quote

Do not use on a full moon or in a forest, next to a large tree.

that's a limiting factor on their stone for sure grinning smiley grinning smiley

not sure on silica..

i prefer knives to be 55-60 for outdoor hard use knives personally because of the ease of maintenance. and I like 60-62 for home knives etc for their better stability and still easy to sharpen. I'm more focused on grindablity than hardnes.. a 55d2 is still going to suck over 60rc 01

in some ways knife choices can be like gun choices.,
do you want some super duper thing that if you run out of ammo you can't get ammo anywhere,
or you you pick the user gun where you know you can find ammo everywhere?

torches, same.. i pick AA battery every time.

the best cannot be the best if you cannot use it when you need it.





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It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
cKc
Re: Selecting the right Geometry
June 07, 2020 01:54PM
the above knife compared to a new swissa farmer blade for perspective



reprofiling again. this time im drawing vertical sharpie markers to get more precise estimations of the angles grinning smiley
calculations are estimated based on
thickness 1mm
spine to apex 14mm
raising spine 1mm
total height 3mm x 14mm is an included angle of 12, 6DPS
finish on dmt fine, now about 5.5dps...

black sharpie, marked on the above bevel before raising and stabilizing




at 10dps as a microbevel, 2 violent cuts into bamboo skewer cutting clean at nearly 90degree left small deformation in the edge
this edge clean cut bamboo with this minor deformation


boosted it to 20dps and it was requiring a lot more force to cut bamboo.
and got more damage, possible from pre existing fatigue. 20dps to 0.003"


what this shows is that very thin can do hard work with a little damage, but if you try to strengthen too thin with a thick apex, fails worse.
you need to ramp up support to a thicker level to support a thicker micro.

All in all though.. cutting the edge starting again and resharpening is about 2 minutes work, coarse, fine, finish. and you'd not typically be force cutting bamboo like the video.. the video knife was fine because it was more like 8dps, with 12dps.. a lot more support.

note even with the damage in the first pic.. it would still clean cut the kitchen paper. this damage is not huge.. steeling would have fixed it

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It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
Re: Selecting the right Geometry
June 07, 2020 03:26PM
Quote
cKc

what this shows is that very thin can do hard work with a little damage, but if you try to strengthen too thin with a thick apex, fails worse.
you need to ramp up support to a thicker level to support a thicker micro.

There is an interesting point here as well about people working with knives and who are looking not just at sharpness, but cutting ability. Take a very nice paring knife, like the Herder, now use it even when it obviously isn't fully sharp and compare that to a utility folder which is sharp. Peel 50 lbs of potatoes with each and really feel your wrist/hands during it.

I did a lot of edge retention work sure, as I was very interesting in understanding how all the factors influenced the results. But I actually used knives, like for work, and it was obvious to anyone just staying sharp was one point, how it actually functioned was far more important. Get your knife ground so that it cuts well first, if it doesn't cut well, what difference does it make if it is sharp.
Re: Selecting the right Geometry
June 07, 2020 03:32PM
Cliff,
That is what I have been asking for sometime. Why the focus on edge retention as the only measurement of a knife? Like you said, a dull Herder paring knife will still cut. I have a video showing that very thing. Why are people not measuring cutting ability in knives vs edge retention?

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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cKc
Re: Selecting the right Geometry
June 07, 2020 03:44PM
Yep. i see so many tests that are not taking into account force and effort. but in the real world its not about sharpness, its about reducing work and effort. efficiency

this is a nice representation of the apex up to 0.01" thick and the differences.. the tiny green bit 0.005" is the representation of the thick micro on the too thin support.. but in general.. you can see that there is a substantial difference in cross section if you get your edges under 10dps except for the very last portion
click image to get full view, but missing is the 0.004, 0,010" thicknesses of the 2 pieces

the 2 green micro bevels are showing the size of a 15dps, and how much is removed once you form 7dps, and have to back it up to 15.
so you will loose less steel if you sharpen to 15, then back bevel to 7, rather than 7 up to 15



----------------------------------------------------------------------
It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
cKc
Re: Selecting the right Geometry
June 07, 2020 03:51PM
these 2 videos are directly following the video above, no interruption.. and before the photo testing above. id done multiple regrinds..
so in this video the apex was subly thinner.. 12-13 and the backing sublty thicker 8-9dps







no real discernable damage..
bambo skewers.. good test.

----------------------------------------------------------------------
It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
cKc
Re: Selecting the right Geometry
June 07, 2020 03:54PM
what im trying to show with all this is that all these variances are in such a tiny area of the edge. its super important to experiment with the type of work you do and the materials.

for normal paring work, I'm not chopping kebab sticks. that original grind will cut a hard carrot-like its not there.

but look at the difference between 15dps, and 12dps, and more importantly the appropriate back support can effect big, small or no failure.

----------------------------------------------------------------------
It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
Re: Selecting the right Geometry
June 07, 2020 04:43PM
cKc,
Yes, but people have to know about the procedure and that you can improve the cutting to suit the task. This is one of the things I have a hard time communicating to other people, they think is is all sharpening prowess, the type of steel, and HT. They are completely missing the point.

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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cKc
Re: Selecting the right Geometry
June 07, 2020 04:58PM
well.. the information is all out there. my opinion is simple. i don't care if someone else enjoys making their life hard.

i don't mind sharing information to those that want to take it, experiment, and see if it helps them

anyone in the other basket is fine to stay there. its good exercise to make cutting hard.

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It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
Re: Selecting the right Geometry
June 07, 2020 05:35PM
Quote
cKc
anyone in the other basket is fine to stay there. its good exercise to make cutting hard.

LOL, they seem quite content doing so actually for the most part.
Re: Selecting the right Geometry
June 07, 2020 08:35PM
Nothingman,
Exactly! I don't get it.

cKc,
I can't seem to get through to people.

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
WordPress YouTube Facebook Patreon Locals Instagram Twitter
Re: Selecting the right Geometry
June 07, 2020 08:55PM
Quote
jasonstone20

cKc,
I can't seem to get through to people.

It was ~20 years ago that Joe and Steve first wrote about how much performance was gained when they reground knives from factory angles/edges to lower angles/more coarse finishes. They were typically taking the 20-30 dps edge down to 15 degrees and leaving them with the medium Spyderco rod finish, or fine DMT.

Look at what people are doing now, still thinking 18 degrees is some kind of extreme/high performance edge. For reference, Cook's book on axes (which is a Bible for most people on Axes) recommends the same angle for a full size axe used for "dirty" work, roots and such. That isn't a high performance cutting grind even for an axe.

If you think your pocket knife needs the same angle as this :



Then something is seriously wrong.

[www.youtube.com]

The reality is that a very simple steel, 50Cr13MoV, which is the basic stainless steel, can easily handle something like :

-1/16" stock or less
-full height grind
-0.005"/10 dps edge

And that knife would out cut and out work every one of those >$500 folders all day long. And IF, anyone wants to argue that they use them all for "hard work", ok that's fine, but why does every review have the knife look like it never cut anything :

[www.youtube.com]
Re: Selecting the right Geometry
June 07, 2020 11:14PM
Cliff,
That is because they barely carry the knife, never mind actually use the knife to cut things with. I explain to people the knives, steels, edge angles, ect I use, which is: a relief grind either flat to the stone or as close as possible, as I can get, as low as an apex angle I can get with the edge still staying intact with cutting, and steels that are Class I or Class II. The response I get is I need a Class III steel, and use angles >15° DPS, so I can see real knife performance. It is like a bad joke.

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
WordPress YouTube Facebook Patreon Locals Instagram Twitter
Re: Selecting the right Geometry
June 07, 2020 11:18PM
Kyley,

From description in your video :

note youtube has this cool new feature.. you don't block people. you "hide" them so that they comment and always see their comments but think that they are being ignored.. however, no one else can see their comments.
its a very troll move on youtube part as someone can be commenting and never told that they are wasting their time. weird right?
so when you don't get a reply from me, you will never know grinning smiley grinning smiley grinning smiley


If it were not apparent, this sounds a whole lot like censorship...