Angles on fixed-angle sharpening systems

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ibrow

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I'm looking to order a fixed angle sharpener and I've been reading threads and gathering info on various products and how they work. Just bumped into this thread: https://www.bladeforums.com/threads/angles-on-clamp-style-devices.1339022/

I have no idea how you all reached the conclusion that the angle doesn't change.

https://ibb.co/1QGBbpT

https://ae01.alicdn.com/kf/HTB1GgDw...-Sharpener-Kitchen-Sharpening.jpg_640x640.jpg

What am I missing here?


EDIT: the angle change might be insignificant, but it still changes lol, it's geometry.
EDIT 2: how do I embed images into a post?
 
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ibrow said:
I'm looking to order a fixed angle sharpener and I've been reading threads and gathering info on various products and how they work. Just bumped into this thread: https://www.bladeforums.com/threads/angles-on-clamp-style-devices.1339022/

I have no idea how you all reached the conclusion that the angle doesn't change.

https://ibb.co/1QGBbpT

https://ae01.alicdn.com/kf/HTB1GgDw...-Sharpener-Kitchen-Sharpening.jpg_640x640.jpg

What am I missing here?


EDIT: the angle change might be insignificant, but it still changes lol, it's geometry.
EDIT 2: how do I embed images into a post?
Click to expand...

I was in the same boat... what you're "missing" is the angle being measured. Take a look at my post and picture from that thread...

angles on clamp style devices

... (here's the picture)...

IMG-1223.jpg


... and you'll see the difference. "Common sense" says it's the angle created in the top picture... but it's actually the angle created as you look down the edge, which doesn't change.

Keep in mind, it's only for the straight part of the edge... not when the blade curves in the belly-to-tip area. (BTW, once you understand this... you'll realize that in a fixed system, the blade is set based on the belly-to-tip area... not the length of the blade).
 
The angles are clearly marked in the sketch I linked. It's the correct angle, and it's smaller. Yes, we're talking about a straight edge. You can't move farther from the pivot and have the same angle lol. Your bottom picture is actually the misleading one. The angle change there is so small that it can't be reliably detected by your crude method. I gave you a sketch from a geometry program that does the calculations. The angle most definitely changes, that's just basic math. That it's very small when sharpening knives is another thing entirely.

EDIT: I didn't mark the angle in the top picture. I marked the correct angle in the sketch, the one between the stone and the line in the x axis plane. The angle change in the sketch is huge, but it illustrates the principle that the angle must change. It's basic trigonometry, I don't understand how you all got confused.

EDIT 2: https://upload.wikimedia.org/wikipe...angle.Right.svg/1200px-Triangle.Right.svg.png

As you increase the adjacent (the "base", the horizontal line of the triangle), which happens when you move farther out with the edge of the blade, you increase the hypotenuse, which is the rod with the stone.

https://keisan.casio.com/exec/system/1223014436

Here it is. Plug a different value for "adjacent a", leave "opposite b" as is (that doesn't change). You'll see that both the hypotenuse and the angle change.

Plugging in arbitrary eyeball numbers, if the rig is 15 cm from the base to the pivot, and the rod 20 cm from the pivot to where the stone touches the edge, then an increase of 2 cm in the hypotenuse (length of rod from pivot to edge) will produce an angle difference of around 2 degrees (2 degrees less). That's tiny to see with floss and the naked eye, but a significant difference when sharpening. These are arbitrary numbers, and I can't do calculations now to see how long the blade has to be to produce this difference.
 
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ibrow said:
The angles are clearly marked in the sketch I linked. It's the correct angle, and it's smaller. Yes, we're talking about a straight edge. You can't move farther from the pivot and have the same angle lol. Your bottom picture is actually the misleading one. The angle change there is so small that it can't be reliably detected by your crude method. I gave you a sketch from a geometry program that does the calculations. The angle most definitely changes, that's just basic math. That it's very small when sharpening knives is another thing entirely.

EDIT: I didn't mark the angle in the top picture. I marked the correct angle in the sketch, the one between the stone and the line in the x axis plane. The angle change in the sketch is huge, but it illustrates the principle that the angle must change. It's basic trigonometry, I don't understand how you all got confused.

EDIT 2: https://upload.wikimedia.org/wikipe...angle.Right.svg/1200px-Triangle.Right.svg.png

As you increase the adjacent (the "base", the horizontal line of the triangle), which happens when you move farther out with the edge of the blade, you increase the hypotenuse, which is the rod with the stone.

https://keisan.casio.com/exec/system/1223014436

Here it is. Plug a different value for "adjacent a", leave "opposite b" as is (that doesn't change). You'll see that both the hypotenuse and the angle change.
Click to expand...


It's been debated many times. before... and eventually most see it the way it is. ;)

https://www.bladeforums.com/threads/angles-on-clamp-style-devices.1339022/
https://support.wickededgeusa.com/p...he-length-of-longer-blades-on-the-wicked-edge
https://www.bladeforums.com/threads/wicked-edge-edge-pro.788007/page-4
https://www.bladeforums.com/threads/geometry-and-kinematics-of-guided-rod-sharpeners.1131476/


You'll come around eventually... holler when you figure it out!
 
You fellas don't understand basic* math.

Btw, what you linked is what I was referring to. Did you even look at what I wrote? The formulas? The 3D diagram?
 
ibrow said:
You fellas don't understand basic* math.

Btw, what you linked is what I was referring to. Did you even look at what I wrote? The formulas? The 3D diagram?
Click to expand...

ibrow said:
...

As you increase the adjacent (the "base", the horizontal line of the triangle), which happens when you move farther out with the edge of the blade, you increase the hypotenuse, which is the rod with the stone.

https://keisan.casio.com/exec/system/1223014436

Here it is. Plug a different value for "adjacent a", leave "opposite b" as is (that doesn't change). You'll see that both the hypotenuse and the angle change.

Plugging in arbitrary eyeball numbers, if the rig is 15 cm from the base to the pivot, and the rod 20 cm from the pivot to where the stone touches the edge, then an increase of 2 cm in the hypotenuse (length of rod from pivot to edge) will produce an angle difference of around 2 degrees (2 degrees less). That's tiny to see with floss and the naked eye, but a significant difference when sharpening. These are arbitrary numbers, and I can't do calculations now to see how long the blade has to be to produce this difference.
Click to expand...

Sure. In fact, look at the calculator you linked to, where you say "plug in a dfferent value for "a, leave b as is (that doesn't change). Now look at my picuture. B is the height from the base (actually the angle bar) to the knife edge, correct? So, what is 'a"? That would be the angle setting on the W.E., correct? This also doesn't change, as you move down the blade. That's the angle being measured.
 
The actual question to be asked is if you're wondering if fixed angle sharpeners work as advertised (yes, most of them are very good) or if you're more interested in debating the mathematical minutiae about the precision of the angle (which it seems like you're actually doing).
 
If you feel the need to deal in absolutes, then yes the angle does change in some fashion from the straight section to the curve sections, from choil to tip. But with regards to a knife, the difference is so small as to be mute. If you're looking for a system that's gonna hold an angle from here to mars you wont find it. If your looking for a sharpener that puts a kickass edge on a blade, there are plenty.
I have to say it appears your "splitting hairs" so to speak. (pun intended)
 
cbwx34 said:
Sure. In fact, look at the calculator you linked to, where you say "plug in a dfferent value for "a, leave b as is (that doesn't change). Now look at my picuture. B is the height from the base (actually the angle bar) to the knife edge, correct? So, what is 'a"? That would be the angle setting on the W.E., correct? This also doesn't change, as you move down the blade. That's the angle being measured.
Click to expand...

Where's your picture, first of all? Secondly, the angles are calculated in the 3D conical sketch I linked. They're obviously different. It's not empirical, it's mathematical proof. The only thing you can argue is that those are not the angles we're concerned with.
 
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sickpuppy1 said:
If you feel the need to deal in absolutes, then yes the angle does change in some fashion from the straight section to the curve sections, from choil to tip. But with regards to a knife, the difference is so small as to be mute. If you're looking for a system that's gonna hold an angle from here to mars you wont find it. If your looking for a sharpener that puts a kickass edge on a blade, there are plenty.
I have to say it appears your "splitting hairs" so to speak. (pun intended)
Click to expand...

Yes, I even said the angle change is minute, and the angle sharpeners do a great job and most certainly work. However, once I plugged the numbers, I'm not sure the angle change is insignificant. A very large fixed knife might produce a notable difference.
 
cbwx34 said:
Sure. In fact, look at the calculator you linked to, where you say "plug in a dfferent value for "a, leave b as is (that doesn't change). Now look at my picuture. B is the height from the base (actually the angle bar) to the knife edge, correct? So, what is 'a"? That would be the angle setting on the W.E., correct? This also doesn't change, as you move down the blade. That's the angle being measured.
Click to expand...

No, a wouldn't be the angle setting. a is not an angle, it's a line. I had in mind a system like Edge Pro when I made that 3D model, but it's the same principle.

Looking at the sharpening system horizontally with the edge perpendicular to you, rotate the Wicked Edge rig by 90 degrees clockwise and cut in half.

Now, a is "the height from the base (actually the angle bar) to the knife edge" (it's not height anymore as we rotated the rig), but that "height" (length) changes as you move outward along the blade edge from the center. b is at 90 degrees to a, and c is the length of the floss. Now, when you move along the edge from the center, both a and c increase, and the angle between them gets smaller.

Why complicate with the Wicked Edge? Look at the Edge Pro or KME. Now translate that to the triangle in this link:

https://keisan.casio.com/exec/system/1223014436

Now plug in different numbers for a and look at what happens to c and and the angle between them.
 
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ibrow said:
Where's your picture, first of all? Secondly, the angles are calculated in the 3D conical sketch I linked. They're obviously different. It's not empirical, it's mathematical proof. The only thing you can argue is that those are not the angles we're concerned with. Which is wrong.
Click to expand...

IMG-0525.jpg
 
cbwx34 said:
IMG-0525.jpg
Click to expand...

This is wrong. You mixed up a and b. That's why I had you cut the rig in half and rotate it. That's why looking at systems like the Edge Pro is easier and less confusing.

Can't you see that your b (which is actually a in the triangle diagram) changes in length as you move the floss from the center of the rig along the edge? Both it and the floss get longer, and the angle between them decreases, as demonstrated by the formula linked.

EDIT: if you can, do the same exact thing with a KME rig, and mark the corresponding sides.
 
cbwx34 said:
So, what is 'a"? That would be the angle setting on the W.E., correct? This also doesn't change, as you move down the blade. That's the angle being measured.
Click to expand...

That's not a, that's c, and it does change, and so does the angle.
 
ibrow said:
No, a wouldn't be the angle setting. a is not an angle, it's a line. I had in mind a system like Edge Pro when I made that 3D model, but it's the same principle.

Looking at the sharpening system horizontally with the edge perpendicular to you, rotate the Wicked Edge rig by 90 degrees clockwise and cut in half.

Now, a is "the height from the base (actually the angle bar) to the knife edge", but that length changes as you move outward along the blade edge from the center. b is at 90 degrees to a, and c is the length of the floss. Now, when you move along the edge from the center, both a and c increase, and the angle between them gets smaller.

Why complicate with the Wicked Edge? Look at the Edge Pro or KME. Now translate that to the triangle in this link:

https://keisan.casio.com/exec/system/1223014436

Now plug in different numbers for a and look at what happens to c and and the angle between them.
Click to expand...

We're overlapping posts.

All work the same... Wicked Edge, Edge Pro, KME.... it doesn't matter. What you're talking about is the angle in my top picture..., looking down on the sharpener...

IMG-1223.jpg


... but again, that angle is not the angle relationship between the stone and the knife edge.... it's the bottom picture. If you watch the video i linked earlier... I think it's a TSProf, so similar to an Edge Pro... you'll see the same thing.

Like I said, seems counter to what it "should" be, but it's because you're refering to the wrong angle..... I don't know how else to show it. :)
 
Nevermind, I'm not giving an opinion unless I model it first.
 
this is a big part of why I stick with free hand sharpening ...

now don't get me wrong I would really like to get a Wicked Edge and give it a good chance ... I'm sure after the learning curve ... that it would be much faster and easier to reprofike a blade ...

but I have a feeling I would still reach for my ceramics and strops to jyst touch up my blades at the end of the day.
 
cbwx34 said:
Sure... from 2016....

IMG-0528.jpg


... like I said... been debated a lot. ;)
Click to expand...

You understand how those two yellow lines are longer than the one in the middle? And the distance to the base? Angle is lower there.

Measure the length of those two outward yellow lines and the distance from the point where they touch the outer edge of the ruler and the base. Then plug them in the formula I had linked. Do the same for the middle yellow line. Then post the angles you get.
 
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