bevel angle?

Stacy E. Apelt - Bladesmith said:
Also, the angle isn't constant down the blade. The thickness reduces due to distal taper and the grind height varies as the blade tapers in width. This makes a continuously changing primary angle. If you worked off a fixed jig and filed/ground the angle at an exact number ( say 7.1°) the edge would be wide and flat at the tip and go to a zero edge at the plunge.

I often say that a new maker who builds a filing jig to make his blades is like a guy who goes to a nude beach with binoculars. He may see a close up of a cutie in the buff, but if he would set the binoculars aside, he would see the whole beach full of cuties. The jig just limits you to a small range of only one thing.
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I was thinking about this statement, and I don't think it is entirely true. If someone were putting some sort of flat grind on a typical straight edged field knife that is being made of flat stock (not distal tapered), and they are filing down to a fixed line parallel to the edge as their stopping point, the angle of the blade is going to be the same from plunge to the beginning of the belly because it is all happening in the same plane that is defined by the edge and the filing guide. From the belly to the tip the angle will vary, but in a very controlled and attractive way.

Like this set up:
maxresdefault.jpg


While I agree that grinding by hand is probably best if you have a grinder, my hat is off to anyone who takes the time to use a file instead. And if you're using a file, a filing guide brings a level of control that is almost impossible with a hand file alone. That would be like grinding a knife on a belt while moving it up and down the belt the whole time. So using a guide to efficiently shape the blade is smart, and knowing how to set that up properly is going to take some sort of math, plan and measuring device.
 
First, most every knife is better with a distal taper. That is part of the filing/grinding in shaping the blade. More on that is a moment.

Second, if the tip rises on a bar of steel with no distal taper, as in your photo, the angle will have to increase or the edge will get wider as the tip rises. You do this change in angle by pushing harder as you file or taking more strokes in that area, but the angle is changing. If you doubt this, lets do the math:

The steel is 1/8" thick and there is no distal taper. The blade is 1" high and the tip tapers up. For the point of this example, lets assume a FFG bevel that goes to a zero edge. Measuring the angle at the point where the tip is 1/2" wide - the angle at that spot is 14.2°. At the 1" wide places - the angle is 7.1°. You don't see this difference, and really don't notice it as you grind/file/sand ... but it is there.


Back to distal taper:
To keep the edge angle the same as the tip rises, you add distal taper as the tip rises. If the change in taper ( thickness) is the same proportion to the change in height, then the angle stays constant. .. it is simple math :)

Many blades seem not to have a distal taper, but if you look close or measure with a micrometer, you will see that the blade gets thinner as it approaches the tip.
 
Stacy E. Apelt - Bladesmith said:
First, most every knife is better with a distal taper. That is part of the filing/grinding in shaping the blade. More on that is a moment.

Second, if the tip rises on a bar of steel with no distal taper, as in your photo, the angle will have to increase or the edge will get wider as the tip rises. You do this change in angle by pushing harder as you file or taking more strokes in that area, but the angle is changing. If you doubt this, lets do the math:

The steel is 1/8" thick and there is no distal taper. The blade is 1" high and the tip tapers up. For the point of this example, lets assume a FFG bevel that goes to a zero edge. Measuring the angle at the point where the tip is 1/2" wide - the angle at that spot is 14.2°. At the 1" wide places - the angle is 7.1°. You don't see this difference, and really don't notice it as you grind/file/sand ... but it is there.


Back to distal taper:
To keep the edge angle the same as the tip rises, you add distal taper as the tip rises. If the change in taper ( thickness) is the same proportion to the change in height, then the angle stays constant. .. it is simple math :)

Many blades seem not to have a distal taper, but if you look close or measure with a micrometer, you will see that the blade gets thinner as it approaches the tip.
Click to expand...
I don't think we're talking about the same things.

In the blade pictured, there is no distal taper for all of the straight part of the edge, because the spine parallels it. And the angle remains the same from plunge to the beginning of the belly. The cross section remains the same all the way across. If it was a chef knife with a spine that converged with edge in a big triangle, there will be distal taper, but even then the bevel is constant.

As the belly sweeps up, the distance to the eye hook gets shorter, but it only gets 1/2" shorter over the 20" from the eye to edge. So in the example pictured, the difference in angle from the straight section to the tip of the blade is only .2 to .3°.

And since the edge is converging with the spine, the blade is getting thinner from the beginning of be belly to the tip. I didn't think this was the definition of a distal taper, since every knife with a tip necessarily tapers to a point.

Knives that aren't going to taper starting at the belly would be ones where the distance from edge to spine don't change, like a razor blade or a butcher knife with a spine that curves back to match the belly.


Your example of the bevel doubling doesn't make any sense. If you tried to maintain the same spine thickness from belly to tip, your bevel angle would go from 6° to 90° at the tip and become the spine, never coming to a point, but a spine width chisel:
06501.jpg



Keep in mind that these are all approximations, because there are not just multiple ways of grinding a curved edge, there are multiple ways of measuring the angle. However, all of those ways produce angle differences that are fractions of a degree, not an additional 7° in your example.
 
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Stacy E. Apelt - Bladesmith said:
First, most every knife is better with a distal taper. That is part of the filing/grinding in shaping the blade. More on that is a moment.

Second, if the tip rises on a bar of steel with no distal taper, as in your photo, the angle will have to increase or the edge will get wider as the tip rises. You do this change in angle by pushing harder as you file or taking more strokes in that area, but the angle is changing. If you doubt this, lets do the math:

The steel is 1/8" thick and there is no distal taper. The blade is 1" high and the tip tapers up. For the point of this example, lets assume a FFG bevel that goes to a zero edge. Measuring the angle at the point where the tip is 1/2" wide - the angle at that spot is 14.2°. At the 1" wide places - the angle is 7.1°. You don't see this difference, and really don't notice it as you grind/file/sand ... but it is there.


Back to distal taper:
To keep the edge angle the same as the tip rises, you add distal taper as the tip rises. If the change in taper ( thickness) is the same proportion to the change in height, then the angle stays constant. .. it is simple math :)

Many blades seem not to have a distal taper, but if you look close or measure with a micrometer, you will see that the blade gets thinner as it approaches the tip.
Click to expand...

Only under the condition that the thickness of spine on tip remains the same , 1/8" thick..........Which is impossible, because from the start of curve the tip of the knife is taper ......
 
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Natlek said:
Only under the condition that the thickness of spine on tip remains the same , 1/8" thick..........Which is impossible, because from the start of curve the tip of the knife is taper ......
Click to expand...

It is sorta/kinda possible, but not with the pictured jig. It automatically provides the taper.

But I completely agree with you. There is no way for a knife to come to any sort of acute point without a taper.
 
KD Knifeworks, Don't worry about screwing up. You can't bake a cake without making a mess or something like that. I have a pile of failed knife blades...I save them to remind me that I am not a naturally gifted artist. There are no shortcuts to knife making that I know of. Here's my opinion: grind a blade..,if if it looks bad then try to save it because it is now free practice. Then grind another and so on till you make one that looks good and finish it and pretend you are as good a knife maker as the other guys who do the same thing. Jigs don't work for me and most good knife makers do not rely on them but I do think a small work rest for the grinding wheel helps you do better work. I don't care how long you do this but some days things are going to go south...man up and take a deep breath and go do something else for the rest of the day. If it was too easy who would take pride in doing it? Have fun...be happy...make something nice. Larry
 
LARRYZ10 said:
KD Knifeworks, Don't worry about screwing up. You can't bake a cake without making a mess or something like that. I have a pile of failed knife blades...I save them to remind me that I am not a naturally gifted artist. There are no shortcuts to knife making that I know of. Here's my opinion: grind a blade..,if if it looks bad then try to save it because it is now free practice. Then grind another and so on till you make one that looks good and finish it and pretend you are as good a knife maker as the other guys who do the same thing. Jigs don't work for me and most good knife makers do not rely on them but I do think a small work rest for the grinding wheel helps you do better work. I don't care how long you do this but some days things are going to go south...man up and take a deep breath and go do something else for the rest of the day. If it was too easy who would take pride in doing it? Have fun...be happy...make something nice. Larry[/QUOTE

Do not take this personally, it is not meant as criticism. Its meant as encouragement for new guys FR.

IMHO; having a pile of failed knife blades, does not a knife maker make. Not having a pile of failed blades is probably a better indication of mastery.

There are hundreds of good and accomplished knife makers on this forum that use jigs and fixtures of all types. The ability to think outside the box is the best indicator of a new knife makers future success, more so than their innate ability.

I've worked with many different makers over the last 18 years and what is most interesting is, each has their own process to turning out the final product. The end results may look similar but each craftsman has his or her own approach, its because each of us learns differently. Kinetic, auditory or visual.

Decades of working with my hands has taught me to, "not" work myself into a corner, with my thinking, but instead to look at all the possibilities. This is how each of us finds our own way in making what we make.

Regards, Fred
Click to expand...
 
With a grinder or a file one has to define where is the edge center line and where to bring the grind line up to the spine. The file or the belt have to remove what's in between, blending all the variations in pleasant way... A jig can only complicate things; filework actually prevents screwups since it is very controllable.
 
Fred, I have a SMALL pile of mis ground knives and I have made and sold over 500 knives. Also I do not use this forum to sell my grinding jig as I don't use one. People may judge the quality of my work by looking at it. And, yes Fred I do take this personally because you are selling a product and impugned my ability and opinion. Larry
 
stezann said:
With a grinder or a file one has to define where is the edge center line and where to bring the grind line up to the spine. The file or the belt have to remove what's in between, blending all the variations in pleasant way... A jig can only complicate things; filework actually prevents screwups since it is very controllable.
Click to expand...

Yes, filework actually prevents screwups since it is very controllable. Actually if you ask me , file guide tool is CNC in hand tool equipment :)
First and most important is to grind edge center line , after that is easy .............This is my tool for final sharpening with wet stone , but I also use it for precision grinding with file .

vqgoc1.jpg


On this blank edge is now at 0.6mm and is a straight line as gun barrel ...........:)

dvnk3o.jpg
 
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