400 % more edge holding - convex vs flat

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HeavyHanded said:
REK Knives REK Knives I agree running the convex high has its challenges when you don't want to go all the way to the spine, but then again you can only thin a regular sabre grind so much before you hack into the plunge line and have to regrind the whole primary anyway.
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Not sure I understand when you say that you 'can only thin a regular saber grind so much before you hack into the plunge line'. Are you referring to the secondary grind or the primary? I always use 'saber grind' terminology to refer to the primary grinds. and if I'm regrind the primary to thin it out, then I am necessarily re-doing the plunge anyway ;)
 
razor-edge-knives said:
Not sure I understand when you say that you 'can only thin a regular saber grind so much before you hack into the plunge line'. Are you referring to the secondary grind or the primary? I always use 'saber grind' terminology to refer to the primary grinds. and if I'm regrind the primary to thin it out, then I am necessarily re-doing the plunge anyway ;)
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That's my point I guess. Whether sabre or convex, you're going to be grinding way up the primary if not all of the way to the spine. A response to this:
razor-edge-knives said:
But this is my issue w/ convex grinds, often times when I'm regrinding knives I can't simply raise the grind height because maker's logos are on the flats. So the issue comes in that my customer can either choose flat, convex (or hollow of course) but without being able to raise the grind height the convex won't cut as well.
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So, no longer avoiding the elephant in the room, Bark River often convexes the entire blade profile. This is considerably different than a convex edge.
 
Wow!!! my head is spinning :confused:. You guys are real edge maniacs :cool:. I don't know how much a convex blade holds better than a V or a flat grind. I experienced a lot less rolling and chipping on the convex blades. but at equal or near equal edge geometry I didn't noticed any improvement on pure edge holding on identical steels.
 
Well, I mean this thread went to absolute edge nirvana kinda quickly..... I think I did not get about 50 % of things you said, I really have to read everything once again.
 
Well I think 400% is a lot because geometry has a much greater influence on toughness than wear resistance.
 
The 400% claim is a bunch of horse sht and we all know it. The V grind versus convex discussion is a different matter. There is bo way that a full height convex ground knife will outcut a full height flat ground knife with a secondary bevel of whatever, 15 to 18 dps. Not gonna happen. But a convexed secondary bevel will give a V bevel a run for its money.

Take one CS Trailmaster factory full height convex. Take the same knife and flatten the sides and put an 18 dps secondary bevel. My money is on the V for cutting. Take this same knife and convex the secondary bevel and I have no idea which will cut longer. I think the convex has the edge because the lack of a shoulder reduces drag and thus reduces wear. But I dont really know.
 
I do remember a thread some time back that involved convex edge angles. Here is the problem with determining the angle of a convex edge. If you start at the apex or say 0.01mm from the apex you may have an angle of 35 degrees, as you move away from the apex, the angle is constantly changing relative to the apex. The angle will eventually line up with whatever the angle of the flat or slab side is. So you can determine an angle at a point on the edge, but it will not be the angle of the entire edge. This is just plain fact. I can pick a point 1mm from the apex and it may be 4 degrees, but closer to the edge or apex it will be very obtuse, maybe 35 degrees. And actually, the term for this angle is correctly stated as the slope of a curve and it is continually changing. I guess you can get an average angle maybe, but I just don't see the point. Depending on how slack your belt is your slope will change. A curve has an equation. The equation results are ever changing. I have played with angles on curves a bit and the best I could come up with was y=x^1.36. This to me looks like the profile of a convex edge. Y being the vertical or straight up to the spine from the edge and x being thickness. But again, depending on the slack belt, your convex slope will be different so this number is irrelevant as well. Who really knows!!
 
400 % more edge holding - convex vs flat
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hahahah . . . I couldn't help it. I saw this title when I first came back to the forum this morning and it keeps knocking in the back of my mind :
. . . so . . . if my M4 Para2 . . . not to get too specific . . . lasts a month (I've gone five or six weeks) between touch up. I was cutting (edge trimming actually) a fairly consistent and clean abrasion resistant rubber part . . . which is my edge testing gold standard and I do it most days at work . . . a task that dulls a Case or SAK blade in one day or less . . .
and so if I convexed that M4 Para2 blade that would mean . . . that would mean . . . oh the magic and splendor of it all . . .
I could go 33 years without sharpening my knife ! ! ! !
my normal touch up being once every month . . . 12 months to the year . . . 400 divided by 12.
33 years ! Whooda thought ? ? ?
 
SteelJunkee said:
An increase of 400% is resulting in 5 times more, so you would sharpen every 5-6 months not 33 years lolll
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Haha I knew there was a big problem there.
Thanks.
5 months ?
I'm going for it.

EDIT TO ADD :
Reminds me of the Ad for Cold Steel's Ranch Boss traditional stockman ( a knife for which I pine but haven't pounced for so many reasons). Anyway they say it has CPM S35VN and that if you buy this knife, especially as a gift, the owner many never have to sharpen the edge; the knife is that good.
I'm not sure what giving it as a gift does for the edge holding ability but it, by all lights, MUST be convexed to hold up this well.
 
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razor-edge-knives said:
To determine the best geometry for a specific task, Cliff Stamp has an amazing video on how to do this and it's spot on (see below)
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Thank you
I'm not a blind disciple of CS but I think he doesn't get enough positive words here.

Sorry for being so long winded lol
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I will always read all that you have the generosity to say/type.
I learn stuff in spite of myself.

razor-edge-knives said:
I've been grinding knives for several years now. I have 3 main methods of doing convex, depending on how deep I want to go
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My question first : have you any experience with using or making the following blade shape ?

I have recently been made aware of a grind that ends up with the spine thinner than the mid portion of the main grind. Think a Ti Lite with the ridge down the middle blended into the side until it visually disappears but is still raised.
One might ask why the heck do this ? I understand this is done on some kitchen knives. The knife would be less weak and flexible than a knife that is only as wide as the widest part of the knife I am describing because it has, at least, a fin of metal above to add support and secondly the area above the ridge/widest part of the blade isn't helping produce stiction or suction to slices of food.

Thanks
This is relevant to this thread because I suppose this is a form of convexing a blade.
 
Wowbagger said:
Thank you
I'm not a blind disciple of CS but I think he doesn't get enough positive words here.


I will always read all that you have the generosity to say/type.
I learn stuff in spite of myself.



My question first : have you any experience with using or making the following blade shape ?

I have recently been made aware of a grind that ends up with the spine thinner than the mid portion of the main grind. Think a Ti Lite with the ridge down the middle blended into the side until it visually disappears but is still raised.
One might ask why the heck do this ? I understand this is done on some kitchen knives. The knife would be less weak and flexible than a knife that is only as wide as the widest part of the knife I am describing because it has, at least, a fin of metal above to add support and secondly the area above the ridge/widest part of the blade isn't helping produce stiction or suction to slices of food.

Thanks
This is relevant to this thread because I suppose this is a form of convexing a blade.
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That grind shape is called a seed shaped grind iirc, no I haven't done much w/ that. But a slight convex grind is done generally on kitchen knives to do as you say - prevent stiction on things such as potatoes. One of the best for this I have read is an S grind (convex at the edge, hollow near the spine) but I have not attempted it yet.
 
There are many different edgetypes out there, the main types are flat, convex and concave. You choose the edgetype that fits your knifes purpouse best. No edgetype is superial allround.

Convex edges are not better, or worse, then other edgetypes, it is just a edgetype.

I have convex edges on my outdoor knifes and they works good for me.

Bark River convex holds 2-3 degree convex sphere. FK F1 holds 6 degrees convex sphere. This means that they function very different.

Convex edges have degrees on there convex apex. With a sharpening tool constructed to sharpen also convex edges is it possible, and simple, to adjust the tool to wanted degrees on the apex and also wanted degrees on the convex sphere.
For example, if I want an apex on 26 degrees total edge I adjust the tool to 13 degrees per side - and if I want 3 degrees convex sphere I also adjust the tool for that - and then I sharpen the knife and I get what I have adjust the tool to do for me.
Later can I maintain the edge in exactly the same degrees on apex and the convex sphere = I take away very little material from the blade. And most important, the edge will not change after the maintainence sharpening. I can do it with full control of all angles.

Sharpening tools are not somerthing new. They have been around for more then 1000 years. People that need flat edges use tools, that is the only way to get flat edges. I have earlyer show drawings from the dark ages that show some of those old sharpening tools in another thred. I can show them here in this thred if wanted.

Freehand sharpening have no precision becouse humans cannot come below 3 degrees wobble on the edge - per side.
Those 3 degrees do not come directly, they come slowly as when drips of water destroy a atone - and canyons digs out by water. Also the dirst drip starts the process...
This means that people that do not use knifes often (and sharpen often) never see how the edge change. Knife users knows that edge chanches - and that a knife blade slowly will be grinded away if the knife are in use a lot - and sharpened a lot. I grinded away a blade during 5 years of using a knife. I know people that grinded away a blade in 2 years. They are knife users, not I.

So, yes, convex edges can be grinded, and maintained, by tools that can sharpen both flat and convex edges - and it is easy to do it, just as easy as sharpen a flat edge on the same tool. The reault will be a perfext true convex edge with a perfect sphere - and the tool can be adjusted to sharpen, and maintain any wanted apex degrees and any wanted convex sphere.

Most sharpening tools can sharpen flat edges with high quality and do it in wanted degrees with the help of Angle Cube or similar (or with a built in protractor).

Very few sharpening tools can grind and maintain convex edges in wanted apex degrees and with wanted degrees on the convex sphere.

Thomas
 
EdgePal said:
Sharpening tools are not somerthing new. They have been around for more then 1000 years. People that need flat edges use tools, that is the only way to get flat edges. I have earlyer show drawings from the dark ages that show some of those old sharpening tools in another thred. I can show them here in this thred if wanted.
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I would like to see that. You could post a link so as not to burden this thread.

I do not understand your use of the phrase "degrees convex sphere"—do you mean the circular arc angle? Theta in this figure:

270px-Circle_arc.svg.png
 
2la4ug1.jpg


This picture shows two men working with a sharpening tool and a swors, they are grinding out a fuller or polishing the fuller.
You can se the tool they hold in their hands also help them to hold an angle. The same tool downside part of fabriks or leather can be changed to parts of wood when they sharpen the edge and with those part can they hold a very exact angle.
The antler beside the grinding table holds quarts sand and fat. They have different grits of quarts sand and can go finer and finer during the sharpening process.

English is not my languish. I translate directly from Swedish and describe as we talk in Swedish.
My English is also limmited as you can se.

A convex edge can be meassured in degrees - as in the part of the circle L. We do so here.

Most people do not know how many degrees their convex edges holds ( or even how many degrees their edges holds).
As I wrote above, FK holds around 6 degrees steep convex edge and Bark River use a flatter convex sphere on 2-3 degrees. Both are convex - but there is a very big differance innthwir performance.

People still think that convex is just convex. It is not so. A flat edge is flat in different degrees and it is simple to describe a flat edge and its degrees. Also if the edge have a secondary bevel.

The problem is that it is very hard to describe a convex edge correct becouse we have to describe a curved part of the edge - and also how many degrees the apex holds (the cutting edge).

I can not describe my convex edge so exact that you can make exactly the same convex edge on your knife. Most people can not meassure a convex edge - and my experiance is that most people who owns a FK dont knows their edges.

A normal edge in US are around 40 degrees total. A normal edge in Scandinavia are around 20 degrees total = we have different knife culture.
My forest axes have convex edge on 35 degrees. My splitting axe for firewood holds 45 degrees.
A standard Mora knife have a 11 degree edge + a very thin secondary bevel, nearly noy visble, in 2-3 degrees. The total edge for a Mora knife is then 26-28 degrees.
I use a chopper when I am outdoors, a chopping knife with 20 cm long blade, convex edge with 26 degrees on its cutting edge.

I hope that I have been able to answer your question so that you understand it, if not, learn swedish and come back yo me .

Thomas
 
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