Fixed Angle Knife Sharpening "MYTHS"

[TrumanHW]

It's not quite as simple as logically imagined with your example of rod length. It is a common misunderstanding that comes up regularly.

The fact remains (just as D Diemaker explained) that if you clamp a straight knife at a right angle to the guide rod pivot, then the length does not affect the sharpening angle. (Sharpening angle, not relative angle)

The pitch of a roof as D Diemaker used above is a very good example that often clears up this misunderstanding. Imagine you attach a string to the top of a roof in the center of the ridge. Now pull that string straight down to the eave / gutter. Now pull this string all the way to the left side, or right side of your roof. The string gets longer & shorter as you go left or right and the relative angle between straight down and your current position changes, but the pitch angle of the roof does not change at all. Your sharpening angle is the pitch angle of the roof.

As you move left & right, your relative angle changes and your sharpening stone rolls left & right too but the actual sharpening angle does not change. Unfortunately, a regular digital angle cube has to be rotated at a right angle to the ridge of the roof to measure the pitch of the roof, you can't swivel that angle cube in-line with your string as it's not designed to measure at an angle on the third axis. Some advanced angle cubes are 3 axis cubes, but most are not. This is also where a lot of confusion and erroneous "proof" comes into play with people who do not understand how a basic angle cube should be used.

Now, if your knife is NOT straight, then most definitely the sharpening angle changes. Imagine a tip that sweeps up excessively, closer to your pivot point, or a belly that curves away excessively. Those angles do change. An excessive belly will have a lower sharpening angle and an excessively swept up tip will have a higher sharpening angle.

I hope this makes sense?

No, politely, you're precisely WRONG.
As is the "pitch of a roof" explanation.
(both are but illustrations of how not to understand)

Here, try to look at this graphic and recognize how
it's analogous to the difference between:
- the part of the knife closest to the guide for the rod (the belly)
- vs triangle 'B' which is the triangle when sharpening the tip.

Please ask questions with as much specificity as you can so I can reply...

If you're not getting where "The Triangles" are coming from, consider this
(and the infinite number of triangular relationships along the edge's path)

 

[TrumanHW]

At one point I took this short clip to demonstrate, using a pizza cutter.

hahaha, yeah, it's freaking hard without props or without making a video and showing the measured angle as it changes. But what keeps KILLING ME ... is that in Outdoors55 own video ... THE ANGLE CHANGES as he sweeps the angle-guage across the arc.

What do you think of the upload I just did..? If I could draw
(all but impossible on a computer without a tablet) it'd been easier...

 

[Diemaker]

Don't view it as a triangle, view it as a plane defined by a straight line and a point, there is no angle. The answer is 2 dimensional, not 3.

 

[777 Edge]

it's analogous to the difference between:
- the part of the knife closest to the guide for the rod (the belly)
- vs triangle 'B' which is the triangle when sharpening the tip.

If you're not getting where "The Triangles" are coming from, consider this
(and the infinite number of triangular relationships along the edge's path)

You're mixing up different facts here and coming to the logical conclusion that they result in the same answer. They do not.

You are correct regarding the angle of a upswept tip compared to the belly, but we are discussing a straight blade here.

Yes, the angle of an a excessive belly & extreme upswept tip will differ, you are correct about this fact, but the other assumption is incorrect.

 

[777 Edge]

Here is a video that might help understand.

Watch the video in full, then I'm sure you'll get it.

 

[TrumanHW]

You're mixing up different facts here and coming to the logical conclusion that they result in the same answer. They do not.

You are correct regarding the angle of a upswept tip compared to the belly, but we are discussing a straight blade here.

Yes, the angle of an a excessive belly & extreme upswept tip will differ, you are correct about this fact, but the other assumption is incorrect.

Even if the blade is perfectly straight (like a razor) If it has a length greater than the width of the stones, then, the angle will change. Small at first, as that is how the COSINE changes as a function.

I have a suggestion; why don't you ask Grok or ChatGPT ..?

 

[777 Edge]

I have a suggestion; why don't you ask Grok or ChatGPT ..?

No need to get nasty, we're simply trying to help you understand. Watch the video above, that will help.

 

[TrumanHW]

Don't view it as a triangle, view it as a plane defined by a straight line and a point, there is no angle. The answer is 2 dimensional, not 3.

Okay, well, imagine then that we have a knife with absolutely NO curve. Say ... a razor blade. Except this razor blade is 30-feet long. is the angle at the tip still the same as at the point on the razor closest to the rod-guide..?

And yes, there are planes within the Function.
Eg, the blade's-edge should be thought of as a plane.

May I suggest you amuse yourself by asking Grok to analyze the video (just give it the link to Outdoors55 video) and ask if his roof-analogy is accurate. It'll actually scan the video. Please also upload the images I provided ... and see if Grok is "wrong also." And if Grok "also fails to understand your logic,."

 

[Blues]

Take the snark elsewhere if you wish to continue participating here...

This thread is on borrowed time,

 

[TrumanHW]

No need to get nasty, we're simply trying to help you understand. Watch the video above, that will help.

"Help me" understand? lol

That's like Christina of Lorraine (the Grand Duchess of Tuscany) "helping" Galileo understand the Geocentric Solar System.

It's just not accurate. I've believed false things before. It's not embarrassing. It's just wrong.


(I wasn't trying to be nasty at all; but you didn't provide any data or proofs; only metaphors).

 

[TrumanHW]

Here is a video that might help understand.

Watch the video in full, then I'm sure you'll get it.

The video is ridiculous imo. It's another person who's selling a claim based on nothing but his confidence.
Not nefariously, obviously. he absolutely believes what he's saying. But he offered no DATA. Where's the angle gauge!??
Something we're vulnerable to, which is why it's used in the expression CON man.
Outdoors55 is equally making his assertions with absolute confidence.
Its his confidence in his fallacious metaphor that causes everyone to accept it.
But confidence is no substitute for actual data, facts and logic.
Without an angle gauge it's just a claim. And if our eyes were sufficiently accurate, we wouldn't buy them.

To be clear, I'm not saying it matters. I don't care. I use a FAS.
But IF the actual degrees matter to you, they change. Initially slow,
and then faster, as that's how the tangent Fn works.

If you only care about an effective angle on your knife, this absolutely works.
But if you're offering a logical argument, it shouldn't be based on confidence instead of actual facts.

 

[FortyTwoBlades]

Here is a video that might help understand.

Watch the video in full, then I'm sure you'll get it.

The problem here is he's using a flat straight roof as the analogy, and a flat straight bar as the demonstration piece. Under those circumstances there will be no change in the angle of the plane. Most knives curve, and then you end up with wonk because the relative position of contact shifting in and/or out unless the curve maintains exactly the same spatial relationship. All along the straight portion will be consistent. It will be a shifting angle along the curve.

 

[777 Edge]

All along the straight portion will be consistent. It will be a shifting angle along the curve.

That's the point, exactly.

 

[TrumanHW]

Couple of questions

• 777 Edge​

• FortyTwoBlades​

... if you'll both indulge me:

1. Just to rule out talking past each other, you're not just saying that it's close enough. You're literally saying that it's IDENTICAL, right? As in, if you measured the angle made by the stone at the belly on vs to the tip on a PERFECTLY STRAIGHT knife (a razor's shape), you're still saying it'd be identical on say, a 2-foot long 'razor' ..? Which is what all of our thought experiments are going to be I'd assume)

(FortyTwoBlades: I know you just about answered in the affirmative, but to confirm, even on a 2-foot blade)..?

2. If that is what you're saying to question one, then, what about a razor that's 20-feet long?
Would the angle to the middle (closest) vs the furthest point of the edge also be equal..?


Thanks!

 

[FortyTwoBlades]

That's the point, exactly.

To be clear, I understand the point that you PERSONALLY were asserting, however, that's not the same was what the chap in the video was making. His was a sweeping generalization that was more likely to be interpreted as all blades having a consistent angle throughout, which isn't quite true, though it did illustrate YOUR point well visually as applied to straight blades.

 

[FortyTwoBlades]

Couple of questions

• 777 Edge​

• FortyTwoBlades​

... if you'll both indulge me:

1. Just to rule out talking past each other, you're not just saying that it's close enough. You're literally saying that it's IDENTICAL, right? As in, if you measured the angle made by the stone at the belly on vs to the tip on a PERFECTLY STRAIGHT knife (a razor's shape), you're still saying it'd be identical on say, a 2-foot long 'razor' ..? Which is what all of our thought experiments are going to be I'd assume)

(FortyTwoBlades: I know you just about answered in the affirmative, but to confirm, even on a 2-foot blade)..?

2. If that is what you're saying to question one, then, what about a razor that's 20-feet long?
Would the angle to the middle (closest) vs the furthest point of the edge also be equal..?


Thanks!

It's because the stone is able to ROTATE on the rod. If it were unable to do so the stone would not be able to lie flat on the edge of that blade, but as it moves along the length it gets closer and closer to "rotating" on the face of that plane into a sideways position.

 

[garry3]

Couple of questions

• 777 Edge​

• FortyTwoBlades​

... if you'll both indulge me:

1. Just to rule out talking past each other, you're not just saying that it's close enough. You're literally saying that it's IDENTICAL, right? As in, if you measured the angle made by the stone at the belly on vs to the tip on a PERFECTLY STRAIGHT knife (a razor's shape), you're still saying it'd be identical on say, a 2-foot long 'razor' ..? Which is what all of our thought experiments are going to be I'd assume)

(FortyTwoBlades: I know you just about answered in the affirmative, but to confirm, even on a 2-foot blade)..?

2. If that is what you're saying to question one, then, what about a razor that's 20-feet long?
Would the angle to the middle (closest) vs the furthest point of the edge also be equal..?


Thanks!

The blade could be a mile long and it would be the same.

It's simple geometry that isn't always intuitive and some pretty smart folks over think it.

 

[Blues]

I think the post above is a fitting place to close as all points of view have been presented and going around in circles will not contribute further.