Obtuse Edge Angles

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FlyingMuskrat

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Jan 9, 2006
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I was wondering at what general edge angle knives stop cutting, or at what angle you can no longer make them sharp. Case in point is a Queen Stockman, I am trying to get it sharp at the angles that were put on it at the factory, but it isn't happening. The knife was a birthday present to my father so that is why I am trying to get it sharp at the factory angle.

As a side note, has anyone ever tried a 90 degree included edge on a knife?
 
FlyingMuskrat said:
As a side note, has anyone ever tried a 90 degree included edge on a knife?
Click to expand...

No, but I have cut myself on a sharp 90 degree angle. It is all a matter of pressure, or maybe your definition of cutting. Just imagine hitting your heat on a metal plate with a nicely machined right angle. It will split your head open just fine, but not nearly as well as one honed to a nice 10 deg included angle which will split you head in half and nicely disect your brain in the process :D.
 
You can sharpen all the way up to 90, I've cut myself on sheet metal, which doesn't even have an edge. Whether it's efficient is another thing. I have found obtuse angles work best on steel with a very thin primary grind, and high carbide steel, such as D2. The thinness allows for efficient cutting and fast sharpening, and the more obtuse angle allows for the tendency of carbides getting pulled out of the steel. By more obtuse, I'm talking 20 deg per side or so.

The factory angles on the Queens is very obtuse, good luck with that. I usually thin mine out, sorry if this doesn't help your dilemma.
 
Well I talked to my Father and he said to "sharpen it till it was sharp", so I am taking it to 20 degrees per side.

I guess I was mostly wondering if an edge at 90 degrees included could be used for EDC tasks, such as cutting paper, food, etc.
 
Well, I think as unhelpful you father's advice was, I think he is right. It's always a question of what kind of cutting ability you demand for EDC. Obviously, the thinner and more acute the blade (given the same edge finish) the better it will cut. At some point you might run into durability issues but those are a separate issue (very similar, depending on what kind of durability you require). The angles on my knife have pretty consistantly dropped over time, because my demands have risen. Right now personally I would consider around 12 deg per side pretty much the maximum for EDC, maybe allowing for a microbevel applied by the Sharpmaker. But this is my personal opinon. I don't know what Thom is running his blades these days, but I think it is something pretty close to flat to the stone. So why don't you start with 20 deg and if you think it should be better, slowly decrease the angle. As Cliff once told me (which I think is really good advice): you don't have to do all the work at once.
 
If I go much thinner than 40 included on the main blade, I will get into the etching. And since it will probably not see very hard use, that is a consideration. As you (HoB) said, if He would like it to have better cutting ability, either He or I can reprofile it.
 
If your father wants a sharp knife I would go lower than 20 degrees per side. Even with D2 I would go down to the 10 to 15 degree range. If you have a 15 degree fixture I would start with 15 and see if it was adequate for him.
 
FlyingMuskrat,

You can get an edge that's very sharp to hair and skin with an obtuse angle; even to hardwoods; but to bags, cardboard, and plastics, thin is in! Having seen how a thin S30V edge faired with hardwood last night (I'm carving my own Spork so as not to be a slave to the whims of Taco Bell) and S30V being close to D2, I'd suggest a very thin backbevel with a slightly obtuse edge (i.e. 10 degree back-bevel with 20 degree edge) to avoid chipping.


HoB,

Most of my knives have less than 30 degree edges, but not all have thin back-bevels.
 
Jeff Clark said:
If your father wants a sharp knife I would go lower than 20 degrees per side.
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So would you go so far as to say that a knife at 20 degrees per side isn't sharp? Or do you simply mean that at a given sharpness the cutting ability can be improved quite a bit by lowering the angle from 20 degrees per side?
 
I tend to be subjective in how I use the term "sharp" and I suspect that your father will also be subjective. A knife sharpened at 20 degrees per side will not cut anything as well as a knife sharpened at 15 degrees per side. It will not shave as well, it will not whittle as well, it will not cut cardboard as well, it will not even open letters as well. If you insist on being obtuse you should sharpen all the way to a clean edge at 15 degrees per side then just lightly brush the sides at 20 degrees for a tiny microbevel. That would not be very noticeable.

A stockman comes from the tradition of thin pocket knife blades. Someone who is used to those type of blades is used to higher performance edges than people who are used to "tactical" blades. A stockman should perform like a well-sharpened paring knife. Stockmen (is that the correct plural?) are commonly made out of much easier sharpening alloys than D2. The standards for sharpness with a stockman are higher than for most heavy duty knives. I would generally sharpen mine at about 7 degrees per side with a microbevel at 10. Of course that was usually with a carbon steel like 1084 or 1095. With D2 you probably wouldn't want to go that low.
 
From my own humble experiments, I've concluded that 20 degrees per side is about maximum for what I call sharp. This includes knives I use pretty aggressively, although not on concrete blocks or anything.

I think the edge you get from steeper angles doesn't add very much strength, and the sharpness goes away much faster.
 
Sharpness and cutting efficiency are 2 different things. Sharpness is pretty much independent of the angle. Sharpen a knife at 10 deg, and another at 20, run one thumb down each, both thumbs are cut (don't do this, just an illustration). How well and deeply they are cut is another question. So part of the question is how you define sharpness.

Cutting efficiency depends upon several things, not the least of which is the cutting media, as Thom has shown me. As GibsonFan noted, obtuse angles can dull quicker than acute angles.

What I do, which may or may not be helpful to you, is to thin the edge to the point I start to damage it, then back off slightly. A microbevel is very useful here. You can take edges down to the point that Jeff Clark mentioned, and with a micro bevel decrease the chances of damage.

Here is a picture of my CS stockman. I thinned the edge on the main blade to 24, the spey and sheepsfoot to 18 (these were convenient marks on my edgepro). I did this several years ago, and will probably go even thinner in the future. This is what it looks like, if you can live with the wide bevel, go for it. The performance increase will amaze you. I give my Queen stockmen the same treatment.

http://i137.photobucket.com/albums/q203/sodak_photos/p1010009.jpg
 
Hi Sodak, I'm not certain of the way that your edgepro specifies angles, but from the width of your bevels I assume that it indicates the edge angle (the included angle between the edge bevel faces). This value is twice the honing angle on each side. So when you say that your stockman edge angles are at 24 or 18 degrees it implies that the big blade is honed at 12 degrees per side and the small blades are honed at 9 degrees per side. If I'm right that is about what I would suggest for a stockman.
 
The markings on the Edge Pro is the angle for each side. So it's 18 or 24 deg. a side.
 
Jeff Clark said:
Hi Sodak, I'm not certain of the way that your edgepro specifies angles, but from the width of your bevels I assume that it indicates the edge angle (the included angle between the edge bevel faces). This value is twice the honing angle on each side. So when you say that your stockman edge angles are at 24 or 18 degrees it implies that the big blade is honed at 12 degrees per side and the small blades are honed at 9 degrees per side. If I'm right that is about what I would suggest for a stockman.
Click to expand...

Hi Jeff,

I have also heard that the angle is per side, but my bevels run up pretty high, and I like them thin, so I usually try to grind them that way. I'll try to get out my calipers and measure them to make sure.

I do try for a fairly obtuse microbevel on the D2's, I've had some serious chipping problems and found the microbevel was enough to take care of it without having to regrind the relief any thicker.
 
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