Angles on fixed-angle sharpening systems

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At last...relativity explained. ;)
 
All I know is that all three of these were sharpened on a KME. The top and bottom knives are 3 and a half inches long and the center knife is 12 inches long and the only angle variance I can see is on the very tip of the 12'' knife and I think that was caused by the angle change of the hollow grind as it reaches the tip and it is almost undetectable. It could have also could have been caused by my rushing the task because it only shows on one side of the tip. Guided clamp systems are the way to go for perfectly even edges Op so pick one up and experiment and remember, It's not rocket surgery ;).
doC4hfI.jpg
 
HeavyHanded said:
Simple experiment. Set up something heavy on a table or near a countertop and tie a string to it. Make the string taught and draw it over the edge of the countertop. View it from the long edge of the countertop with the string at 90° to the edge of the counter. Now while still sighting along the counter top begin to move the string back and forth, keeping it taught. The angle you observe the string forms with the counter does not change.

If you shift your line of sight to the plane of your triangle so it is perpendicular, the angles indeed change considerably, but sighted along the line of the countertop (edge) the angle is unchanged.

A similar principle, set a carpenters angle on a table and view it perpendicular, it is 45°. Now rotate it, the angle appears to become less acute, but in fact it isn't changing, only your viewing angle is changing.
Click to expand...

Are we still doing the eyeball thing? Is this your idea of science? Prove the math wrong.
 
Night Rider said:
All I know is that all three of these were sharpened on a KME. The top and bottom knives are 3 and a half inches long and the center knife is 12 inches long and the only angle variance I can see is on the very tip of the 12'' knife and I think that was caused by the angle change of the hollow grind as it reaches the tip and it is almost undetectable. It could have also could have been caused by my rushing the task because it only shows on one side of the tip. Guided clamp systems are the way to go for perfectly even edges Op so pick one up and experiment and remember, It's not rocket surgery ;).
doC4hfI.jpg
Click to expand...

Assuming the middle knife came with a bevel of the same angle throughout, you sharpening it on any of these systems resulted in maybe 1.5 to 2 degrees difference between the center portion where the clamp was and the part of the edge close to the heel (the part that goes to the tip curves so we won't discuss it). You're telling me you can see a difference of, at most, 2 degrees between continuous segments of a few mm thick knife bevel? Doesn't mean they're not there. The folders likely differ by an insignificant amount (tenths of a degree at most).
 
Yes op a parallax is a rare pokemon, very powerful indeed. All kidding aside I do see tiny difference on the tips of blades 12 inches or longer but it's probably just me and my newly acquired sharpening skills. This is what I was talking about on 12'' knife that was clamped in the center of the blade. The edge at the ricasso was the same distance from center as the tip but is perfectly even though.
yTUMJF1.jpg
It looks like it widens out a bit to me but only on this side making me think it was an uneven hollow grind on that side. What do you think?
 
cbwx34 said:
Here's one last picture... going back to the W.E. setup... the angle was set at 20°, and I then put a stone on the rod, and stretched it out as far as I could, and measured the angle, which showed 19.6°.

IMG-1224.jpg


Now, if you looked down on the W.E. (the top photo from my earlier post), you would see a difference of several degrees... agree? .4° is just the error in the setup... certainly not the angle difference you would see in what's probably over a foot of difference.

That's all I got.
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How accurate is the bar being held vs the base of the sharpener? The two have to be parallel, as in get out your tenths indicator and confirm. In my head if the two are parallel then the stone angle will not change. I think the roof analogy is correct, in that we should think of planes and not lines.
 
Ok, I just set up an actual experiment because of all this lol. Check it out.

This is the crude rig: https://ibb.co/5T4Hm6J

I measured, with the ruler that you see on the counter, the adjacents (the distance between the base of the bottle to the tip of each string on the countertop. This was a crude enough measurement as the ruler is so small, but I got 20 cm for the left string and 99 for the right. Then I measured the height from the base of the bottle to the origin of the strings = cca. 25 cm. From this I used the Pythagorean theorem to get the length of the strings (25^2 + 20^2 then sqrt of the result; repeat for other one). I got 32 for left string and 102.1 for right string. From this I calculated the angles using this: https://keisan.casio.com/exec/system/1223014690

I got 51 degrees for left and 14 degrees for right. Huge difference, right?

Now check this out: https://i.ibb.co/6HjY5T4/IMG-1146.jpg
This is what you get eyeballing things. Can't tell a goddamn thing. You'd likely say the angles are the same from this? They have to be, right?

https://i.ibb.co/ph71Sjj/DSC-0573.jpg
https://i.ibb.co/Mhy8X54/DSC-0574.jpg

Wrong.

The counter is the plane of the blade, the strings are the plane of the bevel (and the stone/rod that holds it), and together they make these angles. The distance here is huge. With actual knives, you're looking at anything from a tenth of a degree to 2 or 3 degrees difference (most likely NOT visible by the naked eye of any human on the planet, when inspecting knives).

Anyone can do this with two pieces of string, a ruler, and an iPhone that has the Measure app.


EDIT: can anyone tell me how to actually show the images in the post? This would make everything immeasurably easier to view and understand.
 
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Night Rider said:
Yes op a parallax is a rare pokemon, very powerful indeed. All kidding aside I do see tiny difference on the tips of blades 12 inches or longer but it's probably just me and my newly acquired sharpening skills. This is what I was talking about on 12'' knife that was clamped in the center of the blade. The edge at the ricasso was the same distance from center as the tip but is perfectly even though.
yTUMJF1.jpg
It looks like it widens out a bit to me but only on this side making me think it was an uneven hollow grind on that side. What do you think?
Click to expand...

You're showing different thicknesses of the bevel, while we're talking about angles. You got everything wrong.
 
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ibrow said:
Ok, I just set up an actual experiment because of all this lol. Check it out.

This is the crude rig: https://ibb.co/5T4Hm6J

I measured, with the ruler that you see on the counter, the adjacents (the distance between the base of the bottle to the tip of each string on the countertop. This was a crude enough measurement as the ruler is so small, but I got 20 cm for the left string and 99 for the right. Then I measured the height from the base of the bottle to the origin of the strings = cca. 25 cm. From this I used the Pythagorean theorem to get the length of the strings (25^2 + 20^2 then sqrt of the result; repeat for other one). I got 32 for left string and 102.1 for right string. From this I calculated the angles using this: https://keisan.casio.com/exec/system/1223014690

I got 51 degrees for left and 14 degrees for right. Huge difference, right?

Now check this out: https://i.ibb.co/6HjY5T4/IMG-1146.jpg
This is what you get eyeballing things. Can't tell a goddamn thing. You'd likely say the angles are the same from this? They have to be, right?

https://i.ibb.co/ph71Sjj/DSC-0573.jpg
https://i.ibb.co/Mhy8X54/DSC-0574.jpg

Wrong.

The counter is the plane of the blade, the strings are the plane of the edge, and together they make these angles. The distance here is huge. With actual knives, you're looking at anything from a tenth of a degree to 2 or 3 degrees difference.

Anyone can do this with two pieces of string, a ruler, and an iPhone that has the Measure app.


If you want to see more of how intuition fucks with your mind, check out the Monty Hall problem, or similar problems in probability.

EDIT: can anyone tell me how to actually show the images in the post? This would make everything immeasurably easier to view and understand.
Click to expand...
I'm going to have to go over your calculations when I have less Beers onboard ibrow Lol but to post pics download (Imgur) then click and drag your pics to the "Add image box and copy the link to paste in your thread. Hope that helps
 
Night Rider said:
I'm going to have to go over your calculations when I have less Beers onboard ibrow Lol but to post pics download (Imgur) then click and drag your pics to the "Add image box and copy the link to paste in your thread. Hope that helps
Click to expand...

I'll have to try that. Thanks for the tip.

You're welcome to go over the calculations, they're very basic indeed. Android probably has something similar to Measure app with the level function. Everyone has a phone, or an actual bubble level.
 
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HeavyHanded said:
Viewed from the side, the angles don't change. The math isn't wrong, you're measuring the wrong angle.

I'm done here unless the conversation returns to Ginger vs MaryAnn, I'll wait for the video finale.
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Compare the empirical proof with the 3D model from the original post of this thread.
 
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Your problem is you want to measure lines and we are dealing with planes. You need to put a stone on that line and measure the angle it wants to cut on the edge of your countertop.
 
Diemaker said:
Your problem is you want to measure lines and we are dealing with planes. You need to put a stone on that line and measure the angle it wants to cut on the edge of your countertop.
Click to expand...

I'm done with this thread.
 
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Almost forgot, After copying your image link in Imgur click on the Image tab in your thread to post that pic.
SuQPRnr.jpg
 
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