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 Post subject: Convex edges or not
PostPosted: Fri Sep 06, 2013 9:46 pm 
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Joined: Sat Jul 20, 2013 9:36 am
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Location: Palma de Mallorca Islas Baleares Spain
Convex ~ V edge-p1.jpg [16.72 KiB]
Not downloaded yet
I am new to using bench stones I also use an Edge Pro pro . Now it is possible to convex on the EP by say on a Global thin the blade at 10˚ and then put a micro bevel on at 15˚ then grind at 14-13-12-11˚ and strop the steps out .
To learn control on the bench stones I have tried to hold a steady bevel or micro bevel which is not too difficult when retouching an existing bevel.
My technique improves with practice I have tried to do one or two knives often with new bevels every day for the past month and a half. I am quite happy with the results sometimes especially when putting a thinning bevel on I will convex this slightly then try to put a straight micro bevel onto the edge which I do with the finishing stone or I take the convex to the edge and convex through to the finishing stone.
Now which is best say for a ~Yanagi or a Fugubiki should I aim for straight or convex bevels ? What is correct?
I think possible the best edges I have achieved are a combination so a slight convex bevel to the edge with a straight micro bevel done with the finishing stone .
I can see that a convex edge possible has a smaller contact area with what it is cutting but I am slightly confused as to which is the most suitable or recognised as correct ,
Another approach it to thin to the edge keeping as straight a bevel as possible and then put a straight micro bevel on top .
My gut feeling is to thin with a slight convex bevel then finish with a straight micro bevel .
What would one find on an expensive Honyaki knife ?


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 Post subject: Re: Convex edges or not
PostPosted: Fri Sep 13, 2013 8:19 pm 
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Location: Palma de Mallorca Islas Baleares Spain
This is a quote from Knife forums by Mike Stewart

So in light of this what I now do is say a convex thinning bevel then a steeper convexed cutting bevel I find it very natural to convex and the difference is very noticeable & I would imagine say on a hard Honyaki blade it is the only way to get a good edge since trying to maintain a straight bevel when it takes a long time to to get through the steel I had a similar experience with sharpening a ceramic blade the edge on the ceramic is way sharper than when I bought it after both thinning it and convexing the edge .


I hate to be a Smart Ass - But............

Convex Edges are easier to sharpen than "V" edges because they are not as sensitive to exact angles.

That knack should take a very short period of time to learn or you are over thinking it.

People used Convex edges for eons.

There were no "V" Bevels until 1900 - they were invented to make sharpening cheaper on massed produced Commercial knives.

You can adjust the Thinness or Thickness on any edge - that goes for convex as well as "V" Bevels.

If You have a Mini-Canadian and you want it thinner for perceived better slicing - just lower the spine and remove more metal to thin out the edge.

Saying that Convex edges will not Slice as well as V Bevels is pure Hogwash.

It is very hard to answer a post that is based in Non-Facts.

Proper Convex Edges will cut you to the bone in the blink of an eye - they just don't feel as sharp to the touch.

A.G. Russell always said that a proper Convex Edge is Deceptively Sharp.

Scandi Knives Feel sharper - they are Very Very sharp - they also have little or no support for the edge and go dull very Quickly - Scandi knife lovers will tell you how easy they are to sharpen - those are the two virtues of the Flat Ground to Sharp Scandi. They better be Easy to sharpen - you will be sharpening them often if you actually use them.(Real Use as Opposed to theory)

I did not buy my knife to be sharpening it all the time.

A convex edge will usually hold it's edge 400% to 600% longer than a Scandi Edge of the same steel at the same hardness.

In the field I want to use my knife - Not be sharpening it all the time.

One of our Customers Field Dressed and Cut Down two Elk with his Mini-Canadian - No other knives - he never sharpened the knife during the process.

Has the Guy who posted the question ever done something like that or are we dealing in theory ?

I have been Pondering people's Fascination with these new Fangeled "V" edges - They have only been around for about a hundred years and it seems that people that don't know how to sharpen a knife really favor them.


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 Post subject: Re: Convex edges or not
PostPosted: Sat Sep 14, 2013 3:16 am 

Joined: Tue May 29, 2012 12:29 am
Posts: 946
That post is full of misinformation.


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 Post subject: Re: Convex edges or not
PostPosted: Sat Sep 14, 2013 7:29 pm 
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Location: Palma de Mallorca Islas Baleares Spain
Jason B please advise me on the correct information .
So far geometry seems to bare out the notion that a convex edge is more efficient ; perhaps there is something I am missing which is why I posted the question in the first place!

One thing that a convex edge surly has provided the taper to the edge is slightly convexed as well is that only one part of the arc will touch the medium been cut where as say a Scandi grind the whole of the bevel will bind with whatever is been cut therefore greater friction therefore even if both a convex edged blade and a Scandi edged blade were equally sharp the friction on the Scandi would make it feel less sharp when cutting.


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 Post subject: Re: Convex edges or not
PostPosted: Sat Sep 14, 2013 10:03 pm 

Joined: Thu Jul 04, 2013 5:27 pm
Posts: 56
Hi Jason - I've followed your comments on sharpening and found them a lot of help, especially your series on sharpening you did on Blade Forums. Since you do a tremendous amount of high end sharping professionally you have a much greater exposure to different grinds and edges than most of us. Any insights you could offer would be appreciated.
Ron


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 Post subject: Re: Convex edges or not
PostPosted: Sun Sep 15, 2013 2:49 am 

Joined: Thu Jul 04, 2013 5:27 pm
Posts: 56
I'm going to expand a little bit on the root of my confusion on the entire convex vs V bevel issue. In the past I've looked at some of the threads on different forums and it seems to be typified by by the worst of the internet forum insult tendencies and I tend to lose interest when it descend to that level. The CKTG forum here seems to have some of the more reasonable experts without a personal ax to grind. For example I know who the Michael Stewart is that Leo quotes and I'm unimpressed with someone that simply dismisses everyone the disagrees with him on the issue as " it seems that people that don't know how to sharpen a knife really favor them.". On the other hand websites that I respect like zknifes clearly favor the convex approach. My questions are:
1. Is the increase in convex edge durability just a result of a greater angle at the actual edge that is similar to that obtained with a microbevel if needed?
2, Is there really a decrease in friction with a convex edge? The idea that the medium only contacts a single point on the convex edge would seem to depend on the idea that the medium separates on a rigid plane and that does not reflect what I cut in the kitchen, household or out in the woods. Most items I cut have at least a small amount of give to them and wrap around the cutting edge to some degree.
3. Is the sharpness of the convex edge the same as a V bevel? It seems that the V edge is a more acute angle and is thinner behind the edge, both of which I thought were key aspects of sharpness.

I have an open mind on this issue and I'm not an advocate, which is why I'm asking questions not staking out a position. I use an edgepro which lends itself more to a V bevel but I can at least moderately adapt to a convex approach with a strop if that is the best approach. I would appreciate any clarification.
Thanks....Ron


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 Post subject: Re: Convex edges or not
PostPosted: Sun Sep 15, 2013 3:41 am 

Joined: Tue May 29, 2012 12:29 am
Posts: 946
Convex Edges are easier to sharpen than "V" edges because they are not as sensitive to exact angles.

(BS, its actually the other way around. V edges are only sensitive to angles if you can't sharpen. V bevels are convex if you hand sharpen, humans are not that good.)


There were no "V" Bevels until 1900 - they were invented to make sharpening cheaper on massed produced Commercial knives.

(Right... And we have used stones for thousands of years only for convex grinds)


A convex edge will usually hold it's edge 400% to 600% longer than a Scandi Edge of the same steel at the same hardness.

(Only if the apex angle is larger. If both have the same apex angle they will both hold a edge for the exact same amount of time. For a 400-600% change you need at least a 10 degree angle change in the edge apex. I've done CATRA testing, angle is king.)


have been Pondering people's Fascination with these new Fangeled "V" edges - They have only been around for about a hundred years and it seems that people that don't know how to sharpen a knife really favor them.

(Someone failed history.......)

Those are some of my thoughts on things that stand out in that post. (Yes, I know they were not your comments)


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 Post subject: Re: Convex edges or not
PostPosted: Sun Sep 15, 2013 3:57 am 

Joined: Tue May 29, 2012 12:29 am
Posts: 946
Ron,

1. Convex is thinner not thicker. The only way to make any edge stronger is by increasing the apex angle. Convex typically is a thinning of the bevel shoulder.

2. Yes, a convex edge has less drag because less bevel surface area is contacting any single point of the material being cut. Your thinking on too large of a scale or your convex on the blade in use is not extreme enough.

3. Again, convex is not thicker. All the drawings you have likely seen showing the convex on the outside of the V bevel are by those that do not understand geometry. The only way to have a thicker convex is to have a thicker blade, with blades of the same thickness convex is thinner.

Everything comes down to the final angle at the apex of the edge and everything behind the apex is drag. Convex has less drag so its perceived to be many things it is not.


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 Post subject: Re: Convex edges or not
PostPosted: Sun Sep 15, 2013 4:09 am 

Joined: Thu Jul 04, 2013 5:27 pm
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Jason - Very informative posts, I appreciate it. From most of the pictures I've seen the convexing is done at the apex edge, making the convex higher would thin the blade as you indicate.
Thanks...Ron


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 Post subject: Re: Convex edges or not
PostPosted: Sun Sep 15, 2013 10:12 am 
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Location: Palma de Mallorca Islas Baleares Spain
I have convexed two Globals (the edges were in a bad condition micro chips and marks left from steels) on an Edge Pro it was a long process - I thinned to the edge at 10˚ then micro beveled the edge with my finishing stone at 15˚ -then 14-13-12-11˚ then stropped out the progressions. The most recent time I sharpened these two Globals I did them on bench stones I thinned them a little lower about 8˚ not quite to the edge then refined this until I got to 5K Bamboo then convexed to the edge the result was probable not dissimilar to the EP one except it probable had more of taper . I have created two apexes in the arcs one around the cutting bevel around 15˚ and the other on the thinning bevel 8˚.
It would seem at my level with bench stones that it seems that I get better results if I intentionally convex rather than try to flat bevel .

I wonder should I pursue the quest of a perfect flat bevel in the interests of becoming an expert sharpener ?

This is my aim having now to date sharpened about 70 knives with bench stones and probable have completely changed the bevels on most of them to further discipline my sharpening or to improve the knife performance .

As yet know one has commented on what is the correct bevel for an Honyaki knife ? Which was part of my original question.


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