Why secondary and micro bevels?

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I know they tell you not to, but on my users I customarily hone the primary bevel behind the secondary micro bevel periodically with a coarse stone to keep the overall geometry in check.

I think sharpening technique has a lot to do with it. Sharpening technique and preferences can also have a lot to do with steel selection, heat treating etc.
 
... It's really all relative to the overall blade geometry and the finishing angle at the leading edge.
 
Regardless of what you call it, the secondary bevel aka micro-scandi or micro-convex is doing 100% of the cutting. If the micro version of a scandi and convex work so well and are the "preferred" actual working edge of knife makers, why use a flat or hollow grind at all? Furthermore, with flat and hollow grinds there is actually less steel behind the secondary bevel - again, why are they used? If you doubt me, just weigh two identically profiled blades where one is convex or scandi beveled and one is flat or hollow ground.

I have heard no discussion about the fact that blade geometry changes each and every time you resharpen a hollow or flat beveled blade. Is the blade at optimum geometry when its new or when sharpened the 3rd , 4th, 5th, 13th time...etc - which is the magic resharpening number? With a convex or scandi beveled blade, geometry remains constant. I don't believe this point can be contended.

I obviously don't have the knife making experience many of you have brought to bear on this discussion. The fact is, most of you have forgotten more than I know or care to know about making knives and what is obvious to you is sometimes obscure to me. Thanks again for your explainations and patience.
 
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Tai Goo said:
I know they tell you not to, but on my users I customarily hone the primary bevel behind the secondary micro bevel periodically with a coarse stone to keep the overall geometry in check.
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I do that too, Tai.... it only makes sense, IMO. If you are worried about preserving the "look" of the bevel faces on a user blade, then it really isn't a "user", is it? It's about performance.
 
BMK said:
The misconception about sharpening convex and scandi bevels is fascinating.

1. Convex: get a piece of leather, put some polishing compound on it and move the blade over the leather.

2. Scandi: lay the bevel flat against some abrasive and move the knife - as close to a no brainer sharpening operation as you can get

Both are actually easier to sharpen than any micro or secondary bevel where the angle is a mystery, jigs are often used and maintaining the angle is a conundrum.
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Actually you are refering to honing and keeping up an edge that is already there. If you ever chip out or roll a scandi, you have to reset the bevels. At this point, you have to regrind the entire length of the cutting edge to match the deepest part of the damage. Unless you "jig it up", how can you be sure you are maintaining the original angles? Just laying it flat on the stone won't do it. The processes you describe above are overly simplified and I would hope that you aren't truly approaching sharpening this way and instead, just using these "no-brainer" techniques as hyperbole. If you are making hard use knives, you should expect your customers to damage the edge at some point.... and they should expect a blade that is field maintainable. In my experience, scandi and full convex are too picky about the surfaces they need to be worked on. I learned how to make a convex using stones for my own purposes but I wouldn't expect the average user to know how to do that. Scandis are great specialty edges but do not fare well across the array of cutting tasks expected in the camp... add to that the fact that unless you find a flat abraisive surface and a way to maintain that flat surface, your scandi grind will have a short lifespan. The Scandi grind does not lend itself well to adaptation. If you have all of these wonderfully convenient sharpening tools available at your home or camp, then by all means, use the best working edge suited for the task.


Rick
 
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The illustration just shows different “types” of cross sectional geometries, but keep in mind that there are an infinite number of possible variations with each one. To try and suggest that one “type” will out perform the others in every situation isn’t going to hold water. It sounds more like a sales pitch that anything else.
 
Tai Goo said:
The illustration just shows different “types” of cross sectional geometries, but keep in mind that there are an infinite number of possible variations with each one. To try and suggest that one “type” will out perform the others in every situation isn’t going to hold water. It sounds more like a sales pitch that anything else.
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Exactly.
 
Tai Goo said:
The illustration just shows different “types” of cross sectional geometries, but keep in mind that there are an infinite number of possible variations with each one. To try and suggest that one “type” will out perform the others in every situation isn’t going to hold water. It sounds more like a sales pitch that anything else.
Click to expand...

Exactly.
 
BMK said:
Regardless of what you call it, the secondary bevel aka micro-scandi or micro-convex is doing 100% of the cutting. If the micro version of a scandi and convex work so well and are the "preferred" actual working edge of knife makers, why use a flat or hollow grind at all? Furthermore, with flat and hollow grinds there is actually less steel behind the secondary bevel - again, why are they used? If you doubt me, just weigh two identically profiled blades where one is convex or scandi beveled and one is flat or hollow ground.

I have heard no discussion about the fact that blade geometry changes each and every time you resharpen a hollow or flat beveled blade. Is the blade at optimum geometry when its new or when sharpened the 3rd , 4th, 5th, 13th time...etc - which is the magic resharpening number? With a convex or scandi beveled blade, geometry remains constant. I don't believe this point can be contended.

I obviously don't have the knife making experience many of you have brought to bear on this discussion. The fact is, most of you have forgotten more than I know or care to know about making knives and what is obvious to you is sometimes obscure to me. Thanks again for your explainations and patience.
Click to expand...

In the case of a Scandinavian ground blade I believe this statement is true; but not correct when referring to a convex ground blade. As the blade's height narrows due to sharpening, the width above the convex edge is greater.

Fred
 
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I use full flat grinds, why? Here is why, a knife is a tool made for cutting, the better and less resistance it cuts with the better. The shallower the angle of the bevel, the less resistance, easier faster and more accurate cuts. The high angle at which you grind your blades will make such blades useless for some if not most cutting tasks, I know, I have done such grinds in the past. You continually state that the zero-edge is doing all the cutting, but with a full-flat grind, and a secondary microbevel on a full-flat ground blade the angle is still shallower, thus providing a more acute angle at the very edge.
It also seems to me you are concerned about the amount of steel, or perhaps the strength of the overall knife. Choose a good steel, heat treat it properly, and strength should never be an issue. You are making a cutting tool, not a sharpened crowbar.
It all comes down to how acute the angle is at the very edge, and how much resistance you get from the cutting medium from what is directly behind the edge.
Meaure the angles, and prove me wrong.
This work for hollow grinds as well, but I prefer flats.
Del
 
Agreed, no particular bevel will out perform all the others and yes, any angle can be divided into infinity so there are an infinite number of ways to grind a blade - even a monkey (like me) understands that. Maybe some day I will understand why knives with hollow and flat grinds outnumber knives with full convex bevels (at least) 100:1 instead of the other way around...

ps For the record, I believe the full convex bevel to be superior to the scandi bevel in a wider range of situations and applications. No sales pitch here:)
 
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As far as I can see, the best answer is - Why not ?


The part I find interesting is that until I started reading here, I had never seen a Scandi grind.
What is it about that style that made it so regional?
 
Rick Marchand said:
I eventually settled on a near full flat/slightly convex with a microbevel. The shoulder on the secondary is less than .010" on slicers and .010" to .025" on choppers. A full scandi/sabre grind behave like a chisel, which is why it is often favoured among bushcrafters for woodcraft. A convex edge can be very strong and efficient if done properly (very few do it properly, unfortunately). In the end, it is not so much the name of the grind as it is the way in which it is approached by the maker. I have seen scandi out perform convex... outperform v-grind... out perform... etc...

Asking which grind is better is like asking what the best tasting fruit is...

The answer is "beer", BTW.

Rick
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can you suggest or reference any material on how to do a convex edge,i am very interested in this type of edge,i cant find more than only a few articles on it thanks
 
BMK said:
Agreed, no particular bevel will out perform all the others and yes, any angle can be divided into infinity so there are an infinite number of ways to grind a blade - even a monkey (like me) understands that. Maybe some day I will understand why knives with hollow and flat grinds outnumber knives with full convex bevels 100:1 instead of the other way around...

ps For the record, I believe the full convex bevel to be superior to the scandi bevel in a wider range of situations and applications. No sales pitch here:)
Click to expand...

My guess would be that most of the machines used in large production factories to grind knives only work with flat or hollow grinds. I'm sure there is a machine that will convex a blade but I bet it is more cost effective and efficient to get one to flat or hollow grind.
 
Interesting:


[video=youtube;rKCT5wGV9xA]http://www.youtube.com/watch?v=rKCT5wGV9xA&feature=youtu.be[/video][/URL]
 
Why are you talking about convex now? I though your question was about primary and microbevels vs. scandi grinds with no microbevel.

Del
 
Page 1, Post 1, second sentence (emphasis added):

"Why do many knife makers grind a secondary or micro-bevel as opposed to ginding a single angle or curve as in the case of a Scandi or full convex bevel?"

delbert ealy said:
Why are you talking about convex now? I though your question was about primary and microbevels vs. scandi grinds with no microbevel.

Del
Click to expand...
 
BMK said:
Regardless of what you call it, the secondary bevel aka micro-scandi or micro-convex is doing 100% of the cutting. If the micro version of a scandi and convex work so well and are the "preferred" actual working edge of knife makers, why use a flat or hollow grind at all? Furthermore, with flat and hollow grinds there is actually less steel behind the secondary bevel - again, why are they used? If you doubt me, just weigh two identically profiled blades where one is convex or scandi beveled and one is flat or hollow ground.

I have heard no discussion about the fact that blade geometry changes each and every time you resharpen a hollow or flat beveled blade. Is the blade at optimum geometry when its new or when sharpened the 3rd , 4th, 5th, 13th time...etc - which is the magic resharpening number? With a convex or scandi beveled blade, geometry remains constant. I don't believe this point can be contended.

I obviously don't have the knife making experience many of you have brought to bear on this discussion. The fact is, most of you have forgotten more than I know or care to know about making knives and what is obvious to you is sometimes obscure to me. Thanks again for your explainations and patience.
Click to expand...

In the case of a Scandinavian ground blade I believe this statement is true; but not correct when referring to a convex ground blade. As the blade's height narrows due to sharpening, the width above the convex edge is greater.

Fred
 
Fred,

I stand corrected. The geometry does change with each resharpening of a convex bevel. It would appear that the change is not as dramatic when compared to hollow and flat bevel resharpening though. Thank you for giving me a course correction.

Fred.Rowe said:
In the case of a Scandinavian ground blade I believe this statement is true; but not correct when referring to a convex ground blade. As the blade's height narrows due to sharpening, the width above the convex edge is greater.

Fred
Click to expand...
 
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If you resharpen a full convex grind the same way you made it the first time, it is the same blade geometry. I use the slack belt.
 
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