Thread: How Bevel is Affected by Taping

I may be wrong, but isn't the side labelled A the hypotenuse? So wouldn't the correct formula involve arcsin, not arctan?

James.

Originally Posted by Jimbo

I may be wrong, but isn't the side labelled A the hypotenuse? So wouldn't the correct formula involve arcsin, not arctan?

James.

Jimbo,

You are right, you are wrong.

In my measurements I reduced the razor blade down to a right triangle. The diagram I so poorly drew is essentially the same as the way awesome diagram Seraphim somehow posted (except my edge is pointing toward the right and I called my adjacent side A and my opposite side O). The hypotenusala is actually an imaginary line drawn somewhat through the razor from the center of the thickest part of the spine to the edge.

Brad

Originally Posted by icedog

Jimbo,

You are right, you are wrong.

In my measurements I reduced the razor blade down to a right triangle. The diagram I so poorly drew is essentially the same as the way awesome diagram Seraphim somehow posted (except my edge is pointing toward the right and I called my adjacent side A and my opposite side O). The hypotenusala is actually an imaginary line drawn somewhat through the razor from the center of the thickest part of the spine to the edge.

Sorry, but he's right. you can't just flip the triangle around because your measurements and the equation are dependent on the right angle being in the center of the blade between the honing flats.

The formula for angle, as corrected, is 2 * asin( (T/2) / S), where T is the thickness between the honing flats, and S is the distance from the edge to the part of the honing flat that was used when measuring T.

As for the tape, I've never found the difference in angle to cause a problem when honing. Just leave it on the entire time. The difference in angles also won't cause problems with stropping, unless you've got a huge bevel.

As for the relative rates of spine and blade wear, I think you'll find that the edge always wears faster than the bevel. If it doesn't, then the hone will never touch the edge of the blade - you'll always be in the sort of situation as when you first untape the spine.

Originally Posted by mparker762

Sorry, but he's right. you can't just flip the triangle around because your measurements and the equation are dependent on the right angle being in the center of the blade between the honing flats.

The formula for angle, as corrected, is 2 * asin( (T/2) / S), where T is the thickness between the honing flats, and S is the distance from the edge to the part of the honing flat that was used when measuring T.

As for the tape, I've never found the difference in angle to cause a problem when honing. Just leave it on the entire time. The difference in angles also won't cause problems with stropping, unless you've got a huge bevel.

As for the relative rates of spine and blade wear, I think you'll find that the edge always wears faster than the bevel. If it doesn't, then the hone will never touch the edge of the blade - you'll always be in the sort of situation as when you first untape the spine.

Icedog is right based on his diagram. Don't be fooled by the placement of the vertical lines surrounding the A, be concerned only with their vertical alignment, pointing toward the imaginary adjacent middle line. Perhaps icedog actually measured the hypotenuse though, rather than A?

Originally Posted by hoglahoo

Icedog is right based on his diagram. Don't be fooled by the placement of the vertical lines surrounding the A, be concerned only with their vertical alignment, pointing toward the imaginary adjacent middle line. Perhaps icedog actually measured the hypotenuse though, rather than A?

Yes, that's what he's doing based on his textual description (it's also pretty impossible to measure from the edge to the bisection of the line between the honing flats, because there's steel in the way). But if you measure along the honing line from the edge to the honing flat then you've got to use the arcsin function to get the angle, which is the point Jimbo and I have been trying to make.

I'm certainly not into this as much as some of you guys, but if razors are such crude utilitarian tools, I can't imagine the thickness of a piece of electrical tape is going to make that much of a difference.


Jordan

Originally Posted by jnich67

I'm certainly not into this as much as some of you guys, but if razors are such crude utilitarian tools, I can't imagine the thickness of a piece of electrical tape is going to make that much of a difference.


Jordan

How much is Tim charging these days for his crude tools?

Originally Posted by jnich67

I'm certainly not into this as much as some of you guys, but if razors are such crude utilitarian tools, I can't imagine the thickness of a piece of electrical tape is going to make that much of a difference.


Jordan

I have to agree with this sentiment.

Considering the lengths gone to just to get accurate measurements here for these calculations, and the disagreement about what those calculations should be I'm getting the sense that this is not something Joe, Tim, Josh, or even Maestro Levi figures out before they start grinding away on a piece of soft steel. I for sure doubt that even Mike Blue could be knowledgeable enough to reach the fractional tolerances required by these calculations when predicting the size changes through the tempering process.

So in other words, the Spine angle predicting the honing angle is less a deliberate and accurate attempt to get the perfect edge and more a happy accident we take advantage of when trying for the finest edge possible, and sometimes we are willing to compromise the very finest of edges to preserve beauty or ease our task.

Originally Posted by Wildtim

... I'm getting the sense that this is not something Joe, Tim, Josh, or even Maestro Levi figures out before they start grinding away on a piece of soft steel.

I know that Josh has done this for at least one razor he's made. It's not that hard and only takes a few seconds. But yeah this just isn't that critical of a measurement - it's a pretty big ballpark.