Why does he say, freehand sharpening causes convex edge?

T

thisisallen

Joined
Aug 28, 2014
Messages
73
It seems like whenever I read a thread about sharpening a convex edge someone always comments that freehand sharpening causes an edge to convex. Why though?
 
It's because, to various degrees, freehand sharpeners cannot hold the exact same angle on every pass. The result is a convex edge over the accumulation of passes required to fully sharpen. Obviously, some freehand sharpeners can hold a more consistent angle than others.
 
SCTorrero said:
It's because, to various degrees, freehand sharpeners cannot hold the exact same angle on every pass. The result is a convex edge over the accumulation of passes required to fully sharpen. Obviously, some freehand sharpeners can hold a more consistent angle than others.
Click to expand...
That means that any blade can have a convex edge? That would be the source of my confusion. Because I was thinking that the convex blade grind was a necessary part of the edge being called convex.
 
Correct!
Edges can, and many times are (especially after sharpening by the final user) of a different configuration than grinds.
 
thisisallen said:
Do you need a convex grind in order to get all the benefits of a convex edge?
Click to expand...
I suppose it could be argued. But, I have a handful of Rod Chappel blades that are hollow ground and have the most wicked convex ("Appleseed") edges. Perhaps a convex grind with convex edge gets a stronger overall blade, but in regular usage, I would bet the difference couldn't be told.
 
The degree of convexity is minimal to the point of being meaningless for most(?) free hand sharpeners. It would only be noticeable microscopically. I sharpen free hand and to the naked eye, my edges look like regular V edges.
 
This convex term is way overhyped by some companies to sell more blades and boast about 3x performance and similar crap.It all comes down to thickness of stock,thickness behind edge ,and heat treat.Full convex grinds have their place,especially for chopping wood.Otherwise it comes down to thickness behind edge and thickness of stock.There is nothing magical in full convex grinds or edges....as they sell you the hype.Any freehand edge has some convexity anyways.
 
Anything done freehand or done with handheld tools will not be precise or consistent in comparison to machine tools, fixtured items etc. Freehand sharpening is a great skill to have and certainly is more practical in many situations (in the field etc.), but will never be as precise or consistent as a guided system used properly imo.
 
polish avenger said:
I suppose it could be argued. But, I have a handful of Rod Chappel blades that are hollow ground and have the most wicked convex ("Appleseed") edges. Perhaps a convex grind with convex edge gets a stronger overall blade, but in regular usage, I would bet the difference couldn't be told.
Click to expand...
Thinner behind the edge enhances cutting performance.
 
AlongTheRazorsEdge said:
Anything done freehand or done with handheld tools will not be precise or consistent in comparison to machine tools, fixtured items etc. Freehand sharpening is a great skill to have and certainly is more practical in many situations (in the field etc.), but will never be as precise or consistent as a guided system used properly imo.
Click to expand...
A fixed angle system is inherently flawed with any blade except a straight one.
 
Most people are surprised to learn things like no surface is ever truly flat.
Everything has tolerances, and ultimately we're no better than the stack ups of all those tolerances.

Yeah, my free hand knife bevels are likely compound angles (convex).
but the question is:
1) is it measureable?
2) does it matter?
In my experience, there's no practical, measurable difference.

It's like numbers- consider Pi.

Most people will only ever require 3.14, but some people insist on using 3.14159.
 
I've never liked the description 'convex edge'. I think it gets misinterpreted, when expressed in that manner, and confuses things a lot. Some will attempt to literally 'convex the edge' - all the way up to the apex - in sharpening, which usually results in edge-rounding issues and degradation of cutting performance. The sharpest possible apex on an edge will always be atop something that looks, at least microscopically, like a true 'V' edge, even if the steel behind the edge is more visibly convexed.

To me, the greatest advantage of convexing, either of the edge grind or the overall grind, or both, is the elimination of any hard, crisp shoulders behind the edge which can catch & bind in materials being cut. That's ONE way to improve cutting performance.

Then, to improve cutting performance even more, the thinness of the steel behind the edge makes a difference as well. If the steel behind the edge is thin, AND the shoulders of the edge grind are convexed & blended into the upper blade grind, it reduces the likelihood of wedging (as would happen more with thicker grinds) or binding against a hard & crisp shoulder of the edge grind. And some thick blades with a crisply-ground spine can even bind and drag at the spine itself, when the overall (primary) blade grind is flat or hollow-ground - this is more noticeable in materials that tightly pinch the blade when cutting. Convexing the overall grind can keep the grind at the spine edge from contacting the material being cut.

So, you can reduce drag & friction in several ways, either individually or in a combination of any or all of the following:

(1) Thin the grind overall, to reduce pinching or wedging issues in tough material (wood, cardboard, tough/thick rinds on fruits, etc.)...
(2) Convex the shoulders of the edge grind, to eliminate the binding issues otherwise caused by the crisp-edged shoulders of a conventional V-grind...
(3) Convex the overall grind, all the way to the spine, to keep the spine's edges from contacting & binding and also narrow the width of contact area, reducing friction against the blade itself.
(4) POLISH the convexes at the edge grind and overall, to make the blade as slick as it can be, when in contact with materials being cut.

I think the biggest single contributor to ease of cutting is thinning the grind behind the edge, as much as possible. If that's done really well, then the effects of the grind type at the edge - whether it's V-grind or convex - become less significant. But that's not to say they can't add small enhancements to cutting ease, after the grind is adequately thin.
 
chalby said:
The degree of convexity is minimal to the point of being meaningless for most(?) free hand sharpeners. It would only be noticeable microscopically. I sharpen free hand and to the naked eye, my edges look like regular V edges.
Click to expand...

Idk, I sharpen at really acute angles, and my Wonky edges are quite noticeable.
 
I spent years trying not to make convexed edges when I sharpen a knife. Now it is supposedly a desireable thing? I’m not buying it. These are examples of my free hand sharpening IMG_3302.jpeg

view
 
Last edited:
Keep it simple. Rub blade on stone or plate repeat until you get the results you are after. For me having the ability to sharpen a blade with a folding dmt that I have in my pocket beats the convexed/non convexed/ 15.294657 is the perfect angle etc. And a system will produce different results as the different stones wear. Meaning the angle will change with the stones being thinner or thicker. Not looking to go down that road with anyone now.
 
Bill3152 said:
Keep it simple. Rub blade on stone or plate repeat until you get the results you are after. For me having the ability to sharpen a blade with a folding dmt that I have in my pocket beats the convexed/non convexed/ 15.294657 is the perfect angle etc. And a system will produce different results as the different stones wear. Meaning the angle will change with the stones being thinner or thicker. Not looking to go down that road with anyone now.
Click to expand...

Grind It, till ya find it......
I'm the same way.

7 million imaginary customers couldn't be wrong.....😂😂😂😂
 
You must log in or register to reply here.
Back
Top