Belt Sander VS Edge Temper

[db]

When you do this "splitting hairs!"
trick are you useing a convexed or flat bevel edge?

 

[Dog of War]

Most people would probably think it's pretty ridiculous that a bunch of guys - some with online handles like 'Bill DeShivs' and 'Dog of War', some hiding out at the Convex Mafia Safehouse - can makes hundreds, even thousands of posts to a knife discussion forum.

Besides splitting hairs helps us stay sharp.

 

[Cliff Stamp]

Some time ago I took a few moments to think about and visualize convex vs. flat grinds, and it became obvious that if the final edge angles are the same (disregarding microbevel if any) a convex grind has to have greater relief than a flat grind.

Yes, once you constrain the geometries it allows meaningful discussion. For example, if the apex angle is at the minimum to prevent buckling then what is the general performance for a convex vs flat bevel - and - apply the same constraint to the shoulder. What happens to flat bevel if you use more than one line segment and further are the changes linear in number of segments. Hint consider the change in perimeter/area as a function of number of line segments and determine the limit of the sequence.

So right there's the performance difference, if any, that I think people observe.

Congradulations, you have awoken from the matrix. It is a cross section and not a curvature issue. Unfortunately you are part of a small minority, but the minority is growing. Some makers like Cashen are very vocal in support of a very critical and demanding public, blind acceptance is the way of religion, not science.

Besides at the relatively acute geometries I prefer, there's hardly any difference between an edge or grind deliberately convexed, and a flat grind/edge done offhand.

Exactly right, convex knives praised for cutting ability have very low curvatures. The essential difference in the nature of the convex grinds on a splitting axe and an opinel is that the curvature on the axe is much higher. Consider futher what would happen to an opinel if you inverted the curvature - this is what Alvin Johnston does on most of his knives and it is what turns a splitting axe into a felling axe.

As for the original thread topic, I've seen a lot of expensive tools reground and rough sharpened on grinders, and for someone who has the patience and the skill, ruining the temper isn't a concern .

Indeed, and the level of skill isn't significantly high. It is a far less complex task than the average person has to do each day.

How do you determan what the angle of the convex edge ...

Measure it. This was discussed in this sub-forum in detail some time ago as well as a naming convention developed by myself and several others to specify said geometry.

...and really isn't the angle at the very edge a 0 angle?

No. To achieve a zero degree edge bevel you would need the knife to be the thickness of a sharpened edge.

Not real sure how a person would run a test to compare the two different bevels anyways.

Similar to this :

http://www.physics.mun.ca/~sstamp/knives/model.html

in whatever means you wanted to explore the differences of interest. This issue of course has been studied in detail throughout the development of knives from the basic hand axe and the patterns are obvious if you look at the knives which are refined by use and not subject to the popular fad cultures. You also don't need jigs or rods or guides to produce v-ground bevels for such a comparison. Knife makers do grind flat ground blades by hand with no jigs. Lots of traditional wood working tools have similar purposes, a broad axe for example.

I know you guys are really serious about all this, but don't you think it's getting a little ridiculous?

Being so informed, you can take a $5 no-name folder and give it superior cutting ability and lifetime, ease of sharpening, durability and general versatility than stock knives costing more than ten times as much. Not ridiculous to me. But then again I buy knives to use, not as status symbols. I don't sharpen knives so they look impressive but so they cut well. I don't consider the volume of carbides or popularity to be a judge of steel quality. I consider 60 HRC to be fairly soft, ten degrees a fairly obtuse edge angle and any edge over 0.005" thick isn't a profile optomized for cutting.

-Cliff

 

[db]

“

Cliff said..

Congradulations, you have awoken from the matrix. It is a cross section and not a curvature issue. Unfortunately you are part of a small minority, but the

You imply the curvature is a non- issue. Then you go on to say.
“
Exactly right, convex knives praised for cutting ability have very low curvatures. The essential difference in the nature of the convex grinds on a splitting
axe and an opinel is that the curvature on the axe is much higher. Consider futher what would happen to an opinel if you inverted the curvature - this
is what Alvin Johnston does on most of his knives and it is what turns a splitting axe into a felling axe.

Seems like the curvature has a very large effect.
Quote:

Originally Posted by db
How do you determan what the angle of the convex edge ...

Measure it. This was discussed in this sub-forum in detail some time ago as well as a naming convention developed by myself and several others to specify
Thanks for the non answer. How do you compare a flat bevel and a curved one? Do you just pick the point of measure that is random? 1/8, 1/16, ½ inch up from the edge? Depending on what one you want to be the better? As you yourself have implied you can produce a convex bevel that will cut betteror worse than a flat bevel, and I’m assumeing you mean you can do that by adjusting the curvature. But then you say the curvature isn’t an issue?

As for heating a blade too much with a power sander, yeah it is easy to burn the edge if you don't know what your doing. Once you do know what to do sure it is easy to do correctly. Just like most things aren't difficult if you know how to do them.

 

[Cliff Stamp]

You imply the curvature is a non- issue.

No, what I have said directly many times, which Dog of War also noted in the above is that the main effect people are seeing when knives are adjusted from flat to convex edge bevels comes from the reduction in cross section due to a relief grind and lowering of the edge apex angle, not the change in curvature. Both of these effects can be achieved with flat bevels as was noted by Swaim and Talmadge and which I have quantified in great detail many times in the reviews.

Seems like the curvature has a very large effect.

When I compared a splitting axe and a felling axe I noted that the difference in curvatures was that the felling axe has a lower curvature, i.e., it is less convex. This is contrary to the populary opinion that "convexing" a bevel increases the cutting ability. This of course does not mean you focus on the curvature, the reason that the felling axe cuts better is that the cross section is reduced which Dog of War, gud4u and others understand. You don't focus on the curvatures, you focus on the cross section so produced. Once you do this it will be obvious why you can take a flat bevel and convex it so it cuts worse, or better, or is more or less durable. You will note in each case that it obeys the same dependence on cross section as that is what is controlling the performance.

How do you compare a flat bevel and a curved one?

As I noted in in the above this was discussed in detail here including a naming convention developed my myself and others to describe the convex curvatures which allow meaningful comparisons because you can define both bevels and thus discuss their behavior.

If you wanted to be perfectly rigerous you could either define a convex bevel using multibevels to minimize the deviations in the cross sectional area or directly specify its function. The latter isn't necessary for reasons I have noted in detail for some years now but isn't overly difficult if one wanted to do it.

Both of those approaches are sub-high school level math.

-Cliff

 

[Dog of War]

Congradulations, you have awoken from the matrix. It is a cross section and not a curvature issue. Unfortunately you are part of a small minority, but the minority is growing. Some makers like Cashen are very vocal in support of a very critical and demanding public, blind acceptance is the way of religion, not science.

Thanks. Call me Keanu .... this was one of those things that once I recognized what was actually going on, I could have slapped my head for not seeing it before. This basic understanding cleared up a lot of confusion, in fact gave me a whole new appreciation of convex edges and grinds. Why the convex religious establishment keeps trying to hold on to the mistaken myths when the facts aren't in any way an indictment of convexed egdes, beats me.

db, I think this is the thread Cliff is referring to:

http://www.bladeforums.com/forums/showthread.php?t=408387&highlight=apex

HoB's diagram really captures the way I visualize this.

 

[Cliff Stamp]

I'm sure it can be measured, but probably takes equipment most of us don't have.

You can buy calipers on Ebay for the cost of shipping.

Cliff is the developer of measuring cutting thread to test sharpness?

When I started doing edge retention trials back in 98/99 I developed a number of methods to quantify sharpness. I quickly settled on two stock tests, push cutting thread and slicing light cord under a specific tension to measure push cutting and slicing sharpness respectively. I developed these methods and many others to objectively evaluate many aspects of knife performance as well as ways to analyze, model and present such data. The critical part of measuring sharpness is the following defination which I settled on a few years ago, this is a quote from the reviews reference page :

"Many common tests for sharpness are not well quantified and offer little more than a subjective ranking. To measure sharpness start with a defination : in the limit that the binding ability of materials goes to zero, a measurement of cutting ability will reduce to sharpness. The tests of sharpness commonly used in the reviews are push cutting thread and slicing light cord under tension as these materials exert little wedging force they are a decent approximation of sharpness."

It then goes on to note in detail how these tests are performed including pictures in a reference link, which specific materials are used, and the results for a vast number of blades. There are also drawbacks to both of those tests which have lead to other methods I have developed to eliminate those problems which I will be moving to shortly.

Why the convex religious establishment keeps trying to hold on to the mistaken myths when the facts aren't in any way an indictment of convexed egdes, beats me.

Because facts and logic were never the basis for the arguement in the first place. Plus it never sells well when you spend years using ad hominem methods to attack people who point out you were wrong and then you suddenly admit yeah they were right, so long and thanks for all the fish.

Consider on a related noted why you almost never hear makers critize a steel while they are using it but introduce a new steel as an upgrade and all of a sudden there are all these problems with the old steel which the new one fixes and it is really a high performance steel.

-Cliff