Sharpening wedge and holding the *real* angle

[bgentry]

I've built an adjustable sharpening wedge inspired by the one that Unit showed on youtube. Honestly his is probably better, but mine works for now.

When using it, I've noticed a few things that are related. The concept of "just hold the knife level" isn't quite as simple as it sounds. Which part of the knife should be level? This is *directly* related to the true angle that you put on the edge.

In my mind, the edge angle is measured from the centerline of the blade to the edge bevel. The centerline is perpendicular to the flat back of the spine of the blade. Therefore, this is the "true" or total edge angle.

So, to hold the blade "level", the flat back of the spine needs to be 90 degrees to level. If there is a surface on the knife that is exactly 90 degrees to the spine (like the unsharpened ricasso on some blades), then holding that surface level is "correct" and will produce the edge angle you are after.

But holding any other flat surface of the blade level will *not* give the edge angle you think you are establishing. For example, if you have a full flat ground blade and you hold the flat side of the blade level, you'll actually be establishing an edge bevel angle that is 3 to 4 degrees higher than you think it is, as the FFG has an approximate total included angle of 7 to 8 degrees, which is 3 to 4 degrees per side. I hope this makes sense without me drawing up diagrams.

Given the above, how do you guys that use a sharpening wedge determine what is "level" when you are sharpening? Ricasso? Flat of the blade? Something else? I'm finding it visually difficult to keep the ricasso level as it is so small compared to the rest of the blade. Strong lighting helps, but I'm having a tough time getting started.

Thanks for any insight.

Brian.

 

[richard j]

i would ask unit how he sharpens with his wedge. when i used to sharpen by hand, i would just watch when the edge met the abrasive and hold that angle. you can adjust from there easily.

 

[Jason B.]

From centerline any freehand sharpening will have a variance of about 3-5 degrees (or at least mine does) so the use of a block will only be a reference to the angle applied. If you are holding the blade and moving it down a stone it does not matter if you have the stone angled or a angle wedge to start from YOU are still the main angle control and not a perfect one.

Putting the apex in the center line is something you must feel with freehand.

What is level? The whole knife.

 

[Fred.Rowe]

Makes seance to me.

Fred

 

[unit]

You are correct it is not quite as simple as it sounds, but once you learn what level is, you only have to rotate the knife in that plane as it strokes the medium on the wedge. The wedge eliminates the variable of having to pitch the handle up and down, but is still a far cry from using a fixture.

I am at work today, and have limited abilities to post, but if you have questions, feel free to PM me, and I will help you out all that I can.

In a nut shell (for most typical knives that have symmetrical grinds and bevels) you will want envision the stock before the blade was ground, and hold that level. If you are using a Spyderco, it will be the portion of the blade that indicates the steel type (and country of origin on the other side).

You do NOT use the blade faces on a FFG blade, but the flat portion above (near the spine) a saber grind would be a reasonable example. On a knife with a visible plunge line, you will probably be using the area behind the plunge (as described for the Spyderco above).

If you have LOTS of experience with the knife, you will perhaps naturally be able to hold the knife "level".

Like any type of sharpening, it is going to require a bit of practice to do it VERY well.

Your conjecture that the flat back of the spine needs to be 90 degrees to level (or vertical) is correct in theory, but in practice FEW knives have a spine that is truly perpendicular to the center line of the blade...I have noticed this to be true of many Spyderco models (perhaps a result of how the stock is cut?). Also the spine thickness is small and even if it is perpendicular, it is a small reference (and error is likely going to be larger as a result).

Honestly, how I do it is I hold the knife in my hand and handle it for a few moments (if it is not one of my own that I am familiar with). If the handle is well made, I can usually get a feel for "level" based on this "test drive".

As others have said, there will be some error in any form of freehand (this is IMO a type of freehand) and that error is relative to your abilities and experience. I have measured several of my re-profiles and found my errors to range from less than a degree per side to as many as 3 degrees per side (on radically low angles). If you cannot accept a few degrees of error, I suggest a fixture (Edge pro or similar). In practice (and with practice), you can make some bevels with this amount of error that are both beautiful and VERY high performing.

 

[unit]

Why are you using the centerline of the blade as the reference for setting the sharpening angle? If the centerline of the blade is used as opposed to the bevel itself; the results will be different for every knife sharpened, unless they all have the same bevel angle. A blade with a thick spine will have a different edge than one with a thin spine. My thinking may be completely obtuse and if so I am more than willing to be educated. I do all my sharpening relative to the bevel and not the blades centerline.

Regards, Fred

If you are making a knife, or re-profiling, re-establishing, replacing an existing undesirable bevel, you need a plane of reference for the bevel you are grinding. As an example, you receive a knife that has wildly erratic bevels from someone that UTTERLY failed to "sharpen" a blade with the wrong tools for his/her skill level, and the owner requests that you "fix it".

To your point, for a routine sharpening on a well made knife...you will likely simply match the existing bevels. (edit to add) this can be done with a wedge, and several people report that they find it easier to use the adjustable wedge to find their existing angle, then set the wedge and sharpen the knife. It may not be perfect for everyone or every knife....but I have dealt with a lot of people that like what it does for them.

 

[Fred.Rowe]

I've built an adjustable sharpening wedge inspired by the one that Unit showed on youtube. Honestly his is probably better, but mine works for now.

When using it, I've noticed a few things that are related. The concept of "just hold the knife level" isn't quite as simple as it sounds. Which part of the knife should be level? This is *directly* related to the true angle that you put on the edge.

In my mind, the edge angle is measured from the centerline of the blade to the edge bevel. The centerline is perpendicular to the flat back of the spine of the blade. Therefore, this is the "true" or total edge angle.

So, to hold the blade "level", the flat back of the spine needs to be 90 degrees to level. If there is a surface on the knife that is exactly 90 degrees to the spine (like the unsharpened ricasso on some blades), then holding that surface level is "correct" and will produce the edge angle you are after.

But holding any other flat surface of the blade level will *not* give the edge angle you think you are establishing. For example, if you have a full flat ground blade and you hold the flat side of the blade level, you'll actually be establishing an edge bevel angle that is 3 to 4 degrees higher than you think it is, as the FFG has an approximate total included angle of 7 to 8 degrees, which is 3 to 4 degrees per side. I hope this makes sense without me drawing up diagrams.

Now I understand what your saying.

Fred

 

[Obsessed with Edges]

In my mind, the edge angle is measured from the centerline of the blade to the edge bevel.

Bingo. From the viewpoint of the material being cut, that's the only angle that matters. The material being cut can't see the shape of the blade behind the very edge anyways, and more often than not, it won't matter much. That's not to say the blade's thickness and overall profile won't affect slicing performance (it DOES). But when you're sharpening, the only relevant angle is the included angle of the 'V' formed by the intersection of the two bevels at the very cutting edge itself. So far as the material being cut is concerned, that's the only angle, and the 'blade' simply appears to it as an infinite, flat plane of steel, with a sharp 'V' edge on it. Anything behind that edge will somewhat affect resistance to slicing, but the 'V' at the edge is what gets it all started. The included bevel angle of that edge is only meaningful when each individual bevel is measured in relation to the centerline. We know the centerline is the reference, because on a truly 'perfect' blade (theoretically), the centerline itself would do all the cutting, with a 'zero' degree edge bevel (the only problem is in finding a blade material strong enough to support a zero-degree edge angle ).

So far as I'm concerned, the concept of 'real angle', 'correct angle' or 'true angle' is basically moot. All that matters is, when YOU sharpen a PARTICULAR KNIFE, you use the SAME REFERENCE ON THAT KNIFE every time, when setting the bevel. The quality of the edge depends only on keeping the angle CONSISTENT from stroke to stroke, and from one sharpening to the next, as opposed to conforming/fitting to a known universal standard of reference. Each knife blade is different, so pick a reference on THAT blade, and stick to it. More often than not, for me, I'll use the flat surfaces of the tang/ricasso as the 'level' reference. Presumably, if the blade was symmetrically ground, the centerline of the blade (drawn from center of the spine to the apex of the edge) should be parallel to the flats of the tang/ricasso. And even if it's not quite perfectly matched up, the difference will be minimal and more-than-likely unnoticeable.

I'll add that when I (personally) sharpen my knives, if the existing factory bevel is asymmetrical or otherwise less-than-ideal for my tastes, I'll just put my own new bevels on it anyway. Once the bevel is set as I want it, the only important 'angle' is as I've described above.

All the above potentially goes out the window, if one is simply trying to match an existing factory bevel. Factory bevels are often asymmetrical or off-center, so simply trying to follow that bevel angle may leave it in exactly the same asymmetry, relative to centerline (albeit with a sharper edge, assuming that part's been done correctly ).

 

[bgentry]

In a nut shell (for most typical knives that have symmetrical grinds and bevels) you will want envision the stock before the blade was ground, and hold that level. If you are using a Spyderco, it will be the portion of the blade that indicates the steel type (and country of origin on the other side).

Thanks for confirming this.

Your conjecture that the flat back of the spine needs to be 90 degrees to level (or vertical) is correct in theory, but in practice FEW knives have a spine that is truly perpendicular to the center line of the blade...

I didn't know that. Interesting.

Also the spine thickness is small and even if it is perpendicular, it is a small reference (and error is likely going to be larger as a result).

I was going to say something about that, as I noticed now ridiculous it would be to try this.

Honestly, how I do it is I hold the knife in my hand and handle it for a few moments (if it is not one of my own that I am familiar with). If the handle is well made, I can usually get a feel for "level" based on this "test drive".

That kinda goes with what KnifeNut said above. I'll try that approach some in my coming experiments.

As others have said, there will be some error in any form of freehand (this is IMO a type of freehand) and that error is relative to your abilities and experience. I have measured several of my re-profiles and found my errors to range from less than a degree per side to as many as 3 degrees per side (on radically low angles). If you cannot accept a few degrees of error, I suggest a fixture (Edge pro or similar).

I recognize that this is just an assist to freehand. I think my variance is at least 3 degrees when freehanding. That seems totally acceptable to me.

Brian.

 

[bgentry]

So far as the material being cut is concerned, that's the only angle, and the 'blade' simply appears to it as an infinite, flat plane of steel, with a sharp 'V' edge on it.

This and everything else you wrote in that paragraph was nice to see, as it fit in with what I was thinking. Thank you.

So far as I'm concerned, the concept of 'real angle', 'correct angle' or 'true angle' is basically moot. All that matters is, when YOU sharpen a PARTICULAR KNIFE, you use the SAME REFERENCE ON THAT KNIFE every time, when setting the bevel. The quality of the edge depends only on keeping the angle CONSISTENT from stroke to stroke, and from one sharpening to the next, as opposed to conforming/fitting to a known universal standard of reference. Each knife blade is different, so pick a reference on THAT blade, and stick to it.

Confession time for me: I've only very recently figured out this basic fundamental of blade geometry that we are discussing here: Edge angle is measured from centerline to edge bevel. I didn't know what to think before about "angle" and I used the side of the blade as my reference. I prop the side of the blade against a wedge sitting on the stone and use that as a reference. As a result I thought I was putting 15 degree per side angles on *all* of my edges, when in fact I was putting at least 18 degree angles, and ones that were probably as high as 23 degrees on knives with thick grinds.

*This* is why "real angle" is important to me. Not so much that I can be at some measurable, super precise angle, but more so that I can be closer to where I think I am when trying out the performance of lower edge angles. I hope this makes sense.

That being said, consistency in edge angle is far more important than absolute angle. Guided systems are proof of this.

More often than not, for me, I'll use the flat surfaces of the tang/ricasso as the 'level' reference. Presumably, if the blade was symmetrically ground, the centerline of the blade (drawn from center of the spine to the apex of the edge) should be parallel to the flats of the tang/ricasso. And even if it's not quite perfectly matched up, the difference will be minimal and more-than-likely unnoticeable.

Awesome. This confirms my thoughts. Now to put this into practice!

Thanks again.

Brian.