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putting a convex edge on knife

J

jcs71

Joined
Mar 30, 2006
Messages
138
I tried to do a search but all I keep getting is a blank white page. Please forgive me if this has been asked before.
How in the world do you people put a convex edge on a knife? I would really like to learn this. It could also be the answer to why one of my knives is giving me a problem when it comes to sharpening it. It had a convex type edge. So how do you do it? Thank you.
 
From what I understand you need a sharpening surface with some give. Mousepad with wet/dry sandpaper seems to be a popular method. Pull the edge across in stead of pushing it like on a normal stone. Another method I've heard about and am going to try is a 1x belt sander done in slack mode.

Hope that helps.

Charles
 
Arc the knife over the stone, arc the stone over the knife, or sharpen on a soft surface.

-Cliff
 
If you do it freehand and alternate the pressure on the push and pull strokes, it'll end up convexed. Or sharpen by moving the stone across the side of the edge from ricasso to tip.

Your two best bets are to get a cheapy belt-sander and array of belts in various grits (quick, easy, super-sharp) or ignore the hype, misinformation, exaggeration, and outright b-s told about convex edges and learn to sharpen properly. With freehand, you'll end up with a little convexity no matter what you do. Whether it's outside of the tolerances folks consider flat or not, it'll be quicker and take away less steel from your knife and less time from your life.
 
thombrogan said:
Your two best bets are to get a cheapy belt-sander and array of belts in various grits (quick, easy, super-sharp) or ignore the hype, misinformation, exaggeration, and outright b-s told about convex edges and learn to sharpen properly. With freehand, you'll end up with a little convexity no matter what you do. Whether it's outside of the tolerances folks consider flat or not, it'll be quicker and take away less steel from your knife and less time from your life.
Click to expand...

Actually his best bet is to get some sandpaper and a mouse pad for very few dollars. His knife already has a convex edge and maintaining one is very simple to do with those once you know how. Easier in fact that free-handing a "conventional" double bevel on a stone. Properly done, both will cut very well so there is no need to deride one in order to promote the other. They're different, that's all. You do him a disservice by allowing your subjective opinion take precedence over your aid. Note he didn't ask what we thought of convex edges he asked how to do it, since he "would really like to learn this".
 
A slightly dulled convex edge will touch-up to hair-whittling sharpness with a 1" x 30" sander armed with either a 15 micron SiC belt or leather belt and most any buffing compound much faster than with sandpaper over a mousepad and with less likelihood of rounding over the edge than sandpaper over a mousepad. Should the initial setup costs be daunting (and they can be), sandpaper over a phonebook or even over any hard, flat surface will make it easier to resharpen a convexed edge or convex a flat or concave edge with less risk of rounding over the edge than using sandpaper over a mousepad. If one already has a leather strop glued to a block of wood, sandpaper over the strop works better than over most mousepads. At least, that's been my experience.

Blue Sky,

I provided two ways to do convex edges with sharpening stones and suggested a quicker and easier way with the belt sander. Seconds versus minutes is always nice when time is precious. In dismissing the aura surrounding convex edges, I'm allowing the original poster and every other reader to reconsider the reason for choosing/using convex edges. They do require more steel removal (which requires more time) than flat edges while following the same rules which constrain the behavior of flat edges. You could swim from England to Japan with enough time; but why not take a boat or airplane?
 
thombrogan said:
A slightly dulled convex edge will touch-up to hair-whittling sharpness with a 1" x 30" sander armed with either a 15 micron SiC belt or leather belt and most any buffing compound much faster than with sandpaper over a mousepad and with less likelihood of rounding over the edge than sandpaper over a mousepad. Should the initial setup costs be daunting (and they can be), sandpaper over a phonebook or even over any hard, flat surface will make it easier to resharpen a convexed edge or convex a flat or concave edge with less risk of rounding over the edge than using sandpaper over a mousepad. If one already has a leather strop glued to a block of wood, sandpaper over the strop works better than over most mousepads. At least, that's been my experience.
Click to expand...

Now this is a very useful contribution to the original question.

thombrogan said:
In dismissing the aura surrounding convex edges, I'm allowing the original poster and every other reader to reconsider the reason for choosing/using convex edges.
Click to expand...

One could argue that you did more than "dismiss the aura". Can you not see the negative cast of your post and it's implications? In what way was that appropriate? Again, the question was "how-to" not "should I".
 
db; the voice of convexity in a forest of flatness; taught me how to freehand sharpen by offering this link from Koki Iwahara's website. It led me to get a dvd from Murray Carter who argues the structure of human limbs moving a blade across a whetstone has no choice but to be slightly convexed despite our greatest efforts to prevent such things (my phrasing, not his). Works quickly with benchstones.
 
Thats a really good beginners tutorial thombrogan! Obviously just one way of many, but looks good.
 
I love convex edges--eventually all my knives will have them. I just sharpen everything on the mousepad or leather and sandpaper. They are all moving that direction and they are all hair popping sharp
 
I am a big fan of convex edges. But a acute convex edge or a acute flat v-grind edge makes no difference to performace at least not enough to matter.

I do convex even though I am capable of v-grind edges because the convex edge once formed is FAR easier to keep sharp in daily use. They look freaking cool, take no special equipment and provide a simple way with in my skill set and ability to make a knife my own.

I have a few busse gamewardens with convex edges so good they are works of art... People that use them are ALWAYS amazed.

They really freak out when they ask how I did it and I hand them some sand paper.

Do what works!! You will know it works when the knife cuts good. Every thing else is gravy!
 
One thing I like about convex edges is that they seem to stay sharp a little longer.
 
I'm working on some testing of the pros/cons of convex edges with Sandia Natl Labs this summer. I'll be posting results as we get them. Our experiments will involve a variety of geometries and finish levels against a variety of cutting media with both push and slice cuts. Hopefully the data we generate will help people decide which edge geometry works best for their intended purposes. I'm not sure how many different steels we can test before we run out of funds for the experiment, but we'll at least try to cover the basics; a good stainless, a high carbon, a "super steel" and hopefully something from Hitachi, maybe White or Super Blue.
 
clayallison said:
I'm working on some testing of the pros/cons of convex edges with Sandia Natl Labs this summer. I'll be posting results as we get them. Our experiments will involve a variety of geometries and finish levels against a variety of cutting media with both push and slice cuts. Hopefully the data we generate will help people decide which edge geometry works best for their intended purposes. I'm not sure how many different steels we can test before we run out of funds for the experiment, but we'll at least try to cover the basics; a good stainless, a high carbon, a "super steel" and hopefully something from Hitachi, maybe White or Super Blue.
Click to expand...

Forgot to add the important part: please post your suggestions for the experiment!
 
Now THAT I will be really interested in seeing, Clay! Nothing like good, solid, repeatable results to find the truth in something.
 
clayallison said:
Forgot to add the important part: please post your suggestions for the experiment!
Click to expand...

I'd like to see some metallurgic microscope images of the edge following an edge-trailing sharpening on sandpaper. i use sandpaper on my convex edges and on some V grinds and am very curious about the apparent lack of burr formation compared to most forms of edge leading sharpening on a hard stone, and all forms of edge trailing sharpening on a hard stone (per Verhooven and my own experience). Where is the burr?!!
I get very good edges but have done no side by side retention tests with an edge leading blade, or better yet, a blade convexed on a hard stone using edge leading strokes (something I am currently practicing and will soon attempt on one of my better knives). My suspicion is that the steel gets incorporated into the apex, which would affect retention measurably. I haven't seen any real proof of this in action, but as I said, I haven't done the testing.

HH
 
Most people like convex edges because they are shiny. There is no particular advantage to a convex edge, if you can properly sharpen.
 
Bill DeShivs said:
Most people like convex edges because they are shiny. There is no particular advantage to a convex edge, if you can properly sharpen.
Click to expand...

I agree 80% with that statement. When it comes to thick-bladed knives however, there's a big improvement in using a convex edge. My TOPS C.A.T. knife has a very thick spine. Out of the box it couldn't slice an apple without exploding it halfway through the cut. After convexing it can slice with no issues. I admit this is a limited example, but there is clearly a difference in some applications. Like wise there's no comparison between a hatchet that's been convexed (or at least had the shoulders ground off) and one with a factory V grind. The difference is remarkable, and convexing hatchets and axes is a practice that goes back many years. I have a few old-timey camping books published around the turn of the century, and more than one guide recommended the practice by saying that a smaller hatchet is practically useless until this modification had been performed.

HH
 
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