Convex edges are the best!

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db

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Convex edges are the best. For me they are very easy to put on any knife. They look great. They are as sharp as anything else. They are as strong as anything else. They are very easy to maintain, and keep sharp. You can double bevel them, a primary with a micro, or single bevel from edge to spine or anything in-between. You can adjust how strong or how well they will cut by how much curve you put on the convex, very large curve or a very shallow one.

I’ve convexed most of my knives and all the ones I carry now are convexed. I prefer to hand sharpen on bench hones, but I’ve also used a belt sander for sharpening. The Sandpaper on something soft like a mouse pad just hasn’t worked for me for some reason. My basic method is.
Take my coarsest hone and quickly scrub back and forth with the blade. I figure out how high I want the spine to raise for my final angle, example with of 2 quarters for 14 degrees, and never let myself raise the spine higher than that. I’ll let the spine drop down flat to the stone but not raise over the highest point. Now I’ll scrub on one side for around 50 strokes more or less I really don’t count then I will switch and do the other side. I keep doing this until a burr forms along the edge. I remove the burr with this coarse hone by cutting into the hone at a very large angle 50 degrees?, on both sides. It takes only one or two strokes normally. Now I will go to a medium hone and do the same thing as with the coarse hone. When I get the burr with the medium hone I decide if I want to finish at this level of coarseness or move on to finer and finer. If finer I repete the same steps with each grit level. To finish I use the grit level I’m finishing with remove the burr at the high angle then do a few stropping strokes not raising the spine any higher than the 2 quarter with height and then do 1 stroke on each side edge forward. That is it it really is just that easy to do. To maintain the sharp edge I’ll strop on just about anything a pant leg will do and if at the end of the day it needs a little more I’ll do an edge first stroke on my finishing hone normally 1 per side is enough. No jigs no worrying about angles or keeping them. Very easy to put on and maintain. Easy to keep them looking great. If you scratch up your blade the scratches are easily fixed just strop them out with your finishing hone. Convex edges and blades are the best!!! Give one a try and I think you will be very surprised at how great they are and how easy they are to sharpen and maintain. I hope someone who uses any other method of maintaining or putting on a convex edge will share how they do it also. Any questions? Love them? Hate them? All comments welcome.
 
Sounds interesting. I'll have to try your method.

I've used the sandpaper and mousepad method with complete satisfaction. My "learning curve" was rather slow, because the first knife I convexed was a Cold Steel SRK. It took a while, (a looong while, to learn) but the results were worth the trouble. That big ol' honkin' SRK will now push cut newsprint.:D
 
I do get a lot of teasing. But my mother's maiden name was Bennington, so I guess I'm struck with it.:D
 
I have read much about the glory and wonder of the convex edge but have yet to see or understand how a thicker knife edge can do anything better than a thinner one. Some time ago I read a quotation on one of the forums (apologies for not crediting the author, but I do not remember) that said something like "If a knife can't do everything I want it to do with a thin V-grind, then I don't want the knife". That pretty much sums up the way I feel.
 
As much as I like the performance of the convex edge on my SRK, I will admit it was one HELLUVA lot of work, and for normal sharpening, I much prefer the Sharpmaker.

I think I did the SRK more as a challenge and a leanring experience.
 
Mtn if a thinner edge is what you want then you can put a thinner one on. You can lower the angle and or lower the curve of the convex to a shallow curve or do both. Both will thin the edge. If you find you've gone too thin it's easy to raise the angle and or the curve to thickin the edge a little. It's also easy to blend both ways in and it looks great.
 
Mtn Hawk said:
I have read much about the glory and wonder of the convex edge but have yet to see or understand how a thicker knife edge can do anything better than a thinner one.
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As is often the case with sweeping generalities they have to be false as rarely is anything so trivial to understand. It is simply nonsense to claim the force response to a blade from a media being cut was the same for all media for all types of cutting. But that it actually means to say one geometry is best. Once you consider optomizing geometry from the point of view of dealing with forces on the blade you will also then clearly understand why different geometries exist. You are already half way there when you look at the cross section rather than the geometry which you have done already. Cook discusses this in the "Axe Book".

Will York asked a couple of questions about convex edges recently and I am framing up a responce to his latest question now. I already discussed some issues in the modeling thread in the review forum which discusses how curvature effects performance. At an absolute level, the actual edge on a knife, the part that cuts, is actually flat ground regardless of how you sharpen the knife. Yes it is still flat even if you use a belt sander in the slack region above the platen.

So when you speak of curvature you are always taking about dealing with the wedging forces on the blade not the forces on the edge itself. With this in mind it becomes obvious that there are benefits at times to a convex curvature and a hollow curvatures depending on the force profile of the media. Some times it actually makes little difference because the wedging responce is minimal above the edge. It all depends on the properties of the media.

-Cliff
 
db,

For me, thin edges are the best. If they're convexed or flat; if they're freehand or the results of a jig or machine; if they went on with nary an effort or took weeks, I just can't get enough of what they do. If the edge gets damaged, the edge was either too thick (and required more force than otherwise) or the wrong steel.
 
For sharpening really acute bevels it is hard to argue for other than a hollow grind unless the blade needs significant torque resistance. You just lay the blade on the stone, grind to shape, then raise a little and hone the final bevel. Cosmetics are horrible, cuts exceptionally well. On a curious note, it is actually easier to hone most of the sabre/hollow folders to really acute angles than the flat ground blades for this reason.

-Cliff
 
thombrogan said:
db,

For me, thin edges are the best. If they're convexed or flat; if they're freehand or the results of a jig or machine; if they went on with nary an effort or took weeks, I just can't get enough of what they do. If the edge gets damaged, the edge was either too thick (and required more force than otherwise) or the wrong steel.
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I have to say I really like the way you think. :)So what is your prefered way to apply these thin edges and maintain them?
 
db said:
Go ahead and argue all you want. I work with what I have.
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You don't have an el-cheapo Harbor Freight 8" wheeled wet grinder? The one that cuts slow and threatens to burn out?

Edge thinning is done most often on a DMT D8XX 120 micron diamond hone, though belt-sanders, EdgePro, Sharpmaker, a Norton Crystolon/India, and all manner of sandpaper and strops have all been used.
 
thombrogan said:
You don't have an el-cheapo Harbor Freight 8" wheeled wet grinder? The one that cuts slow and threatens to burn out?
Click to expand...

Nope don't have one of those. How ever, thanks to you and Lee I do have a DMT D8XX, and wouldn't be without it.
 
And to think that you used to not want anything that cut faster than your hardware-store SiC coarse hone. :) Blame Lee! :p

Well, once you've raised a burr using an 8" SiC wet wheel (and cleaned up the mess.. :barf: ) and then sharpened flat to a hone, you'll get a nice edge (convexed, just like you like 'em) that'll cut well even when dull. By dull, I mean slicing edge into a bastard file a few times and the knife will still slice and score.

OTOH, once you've done that with one knife on a slow wet grinder whose motor smokes after a while, you'll want a KMG or Bader-III with a variable speed 2hp controller and aftermarket 14" wheel and hollow-grinding lessons from Tom Krein and Bob Dozier and an array of belts from 3M and you won't buy such stuff or use the wet grinder too often afterwards.
 
thombrogan said:
And to think that you used to not want anything that cut faster than your hardware-store SiC coarse hone. :) Blame Lee! :p

LOL yeah I know. I'd still recomend that cheapo stone for the price it cann't be beat. I think I could get a life time of them for what I paid for the D8XX.

Well, once you've raised a burr using an 8" SiC wet wheel (and cleaned up
the mess.. :barf: ) and then sharpened flat to a hone, you'll get a nice edge (convexed, just like you like 'em) that'll cut well even when dull. By dull, I mean slicing edge into a bastard file a few times and the knife will still slice and score.

OTOH, once you've done that with one knife on a slow wet grinder whose motor smokes after a while, you'll want a KMG or Bader-III with a variable speed 2hp controller and aftermarket 14" wheel and hollow-grinding lessons from Tom Krein and Bob Dozier and an array of belts from 3M and you won't buy such stuff or use the wet grinder too often afterwards.
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The last thing I really need is more grinders and sharpening stuff. :)
Btw my thin edges do still cut when dull that I put on some of my knives as they are now.
 
thombrogan said:
... and hollow-grinding lessons from Tom Krein and Bob Dozier and an array of belts from 3M and you won't buy such stuff or use the wet grinder too often afterwards.
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Dozier grinds way too thick for that type of knife, Krein goes thin enough, similar to Johnston on request. You don't need to buy a high end belt grinder though, you just need an angle grinder and a washing machine motor and some imagination. Alvin has described his hacked equipment in detail on rec.knives and he has used it to grind full hard M2, and since the majority of knives are butter soft stainless or carbon steel at 58 HRC, its childsplay to grind them in comparison. If you want them to cut well when dull though, don't use M2, get a blade in D2/440C or similar. The large carbides keep tearing out and basically the edge serrates itself.

-Cliff
 
db--

Thanks for your response. I freehand sharpen most of my knives so am probably putting on a slightly convex edge, anyway.

Given the same angle, I know the convex edge bulges out somewhat compared to a V-edge. I have a difficult time imagining how more metal is easier or better to cut, slice, chop, or whatever, through any material than less metal.

Cliff--

If you read what I wrote you will see it is from personal experience and observation, NOT written as THE ULTIMATE SHARPENING TRUTH. There is a big difference.

thombrogan said:
If the edge gets damaged, the edge was either too thick (and required more force than otherwise) or the wrong steel.
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Thank you for stating this so well, and so succinctly.

The "wrong steel" is what I am referring to in my first post on this thread.

As for the edge being too thick, this was a very interesting and important concept for me when I first heard it (I think from Cliff Stamp). Until then I thought that a major reason for edge damage was because the edge was too thin, not thin enough (within reason, of course). This concept changed my sharpening philosophy in a big way and, of course, I get MUCH better performance from my knives.
 
Mtn Hawk said:
db--

Thanks for your response. I freehand sharpen most of my knives so am probably putting on a slightly convex edge, anyway.
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Yup, I'm willing to guess that you are putting on a convex edge. It's almost impossible to not put a convex edge on without a jig.

"

Given the same angle, I know the convex edge bulges out somewhat compared to a V-edge. I have a difficult time imagining how more metal is easier or better to cut, slice, chop, or whatever, through any material than less metal.

I'll just refer back to my post, #7 above.
 
Mtn Hawk said:
I have a difficult time imagining how more metal is easier or better to cut, slice, chop, or whatever, through any material than less metal.
Click to expand...

It general it doesn't, however you have to consider the required cross section as a function of height above the edge. You can't for example just take any convex bevel and replace it with a single flat ground one and assume the knife will still be functional because on some media, at some point the flat ground edge will fail due to lack of strength. From a basic perspective consider a typical full flat ground knife has a 5 degree primary and a 20 degree edge bevel. As you move back from the edge you don't need the obtuse angle past a certain point. Some more consideration to the same physical principles should make it obvious that it is likely that a more complex geometry is probably more optimal. It depends on the force responce of the media being cut. In some cases this produces a convex bevel, in some cases it doesn't. More detail :

http://www.bladeforums.com/forums/showpost.php?p=4001879&postcount=35

As for freehanding producing a convex bevel, if the stones wear significantly, or you are very sloppy, or intentionally rock the blades this is true. It isn't otherwise which should be obvious because many flat ground blades are hand sanded/ground without jigs. Even with stones which wear or hand angle tolerance, the degree of curvature is very slight. Even on fast dished stones like 200 waterstones, it produces a curvature of 1-2 degrees. This isn't significantly different from two flat bevels, the higher the curvature the more line segments would be needed to produce a given tolerance to the difference. Most convex edges which people praise are either basically flat with no curvature or a very slight curvature. No one picks up a hardware store axe for example and rants about how great the convex edge cuts and that has a very severe convexity. The actual extent of curvature is a measure of how obtuse the angle is at the apex compare to the shoulder. The lower this difference, the closer it is to a flat grind.

-Cliff
 
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