How do you know the angle of the edge?

L

Littlefinger

Joined
Oct 30, 2008
Messages
3
Hi,

New to the forums.

I a have some old knives around. How do I know what angle they were factory sharpened at?

Is there a general rule for what angle the edge should be for different tasks?
chopping, slicing, hacking, piercing?

Does anyone know what angle surgical scalpels are sharpened at? Are they just like normal gillete razors?
 
If you don't know the angle of the blade you can try sharpening it at a given angle, then inspecting the edge to see where you're grinding. If you just see marks at the top of the bevel rather than the very edge, use more obtuse of an angle. If you're forming a microbevel, use more acute of an angle with your strokes.
 
Vivi, that is a smart way of doing it.
But what do you mean by microbevel?

What about if you want to go one step further and somehow measure the edge down to the correct degree, any ideas on doing that?
 
If they are fixed blades that you are going to use for chopping 20 degrees would suffice.

If you are talking about slicing 15 degrees would do.

Since you said "old knives" I'm guessing none of them are zdp189, s30v, d2, or s90v. If any of your knives are these steels sharpen at 15 and hack away.

Here's a glossary to look up knife terms like "micro bevel"
http://www.spyderco.com/edge-u-cation/glossary.php
 
When sharpening a knife with an unknown angle I use a black magic marker to color the blade's edge. Then adjust my sharpmaker settings to the correct angle.
 
DaveinNY said:
When sharpening a knife with an unknown angle I use a black magic marker to color the blade's edge. Then adjust my sharpmaker settings to the correct angle.
Click to expand...

Isn't the "correct angle" dependant on what the knife is going to be used for?

I mean you wouldn't neccesarily sharpen a knife at 20 degrees and slice peaches with it. I know you could, but why would you?

I use the black marker trick to practice free handing. To make sure I am sharpening at a consistent angle.

I'm not trying to argue just didn't want Littlefinger to sharpen a knife at 15, go chop on something, and end up with a bunch of chips in the blade.:(
 
I might be off-base here, but I think in the first part of his post LittleFinger is asking: How do you determine the correct angle? Some already posed what they do to find the angle, like using a Sharpie or examining grind marks (I use the Sharpie / Sharpmaker method), but I have the same question: How can we accurately measure the correct angle of a knife that we have?

I've tried using a relatively high-quality protractor with less than limited success. It's hard to see when the protractor is touching both sides of a v-grind, especially on smaller knives or even large blades with a fine v-grind. So, I resort to the Sharpie, then grind on the Sharpmaker to get a basic idea what the grind angle is.

I know it's a two-part question and the second part has been answered, but I'm wondering about the first part (question) of the post.
 
StretchNM said:
I might be off-base here, but I think in the first part of his post LittleFinger is asking: How do you determine the correct angle? Some already posed what they do to find the angle, like using a Sharpie or examining grind marks (I use the Sharpie / Sharpmaker method), but I have the same question: How can we accurately measure the correct angle of a knife that we have?

I've tried using a relatively high-quality protractor with less than limited success. It's hard to see when the protractor is touching both sides of a v-grind, especially on smaller knives or even large blades with a fine v-grind. So, I resort to the Sharpie, then grind on the Sharpmaker to get a basic idea what the grind angle is.

I know it's a two-part question and the second part has been answered, but I'm wondering about the first part (question) of the post.
Click to expand...

Hi,

As you've learned, common tools like protractors are next to worthless. To be able to measure that small, you need to magnify the part you want to measure and then you need the correct scales. I personally would use an optical comparator. An inspection tool that can be had for $2000 to $10,000, depending on how big and fancy. And even then it wouldn't mean a whole lot as even new from the factory, the angle will change from run to run. Even shift to shift and operator to operator.

So, don't get so hung up on exact angles. There really isn't that much difference you can notice in the real world. No commercial sharpener ever made will provide for an exact angle. If they can hit within a couple of degrees either side for the marked angle, consider yourself lucky. Well, I could make it happen but it would require a surface grinder, sine bar, and a set of gage blocks, (and it STILL wouldn't be perfect. Just really, really close). And when you start free-handing, exact angles will mean even less.

If you want to match the factory angle, use the black marker technique as mentioned above. It's fast and easy to do. If you don't like angle, sharpen shallower for easier slicing, but less strength, or more obtuse for a stronger but not as good slicing edge. Experience will teach you what is best for you. Since we all use our knives a bit differently.

So relax, spend less time obsessing, and more time trying. And soon you'll have your knives so sharp they'll cut you if you just look at them wrong.:D

dalee
 
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Littlefinger said:
Vivi, that is a smart way of doing it.
But what do you mean by microbevel?

What about if you want to go one step further and somehow measure the edge down to the correct degree, any ideas on doing that?
Click to expand...

To your latter question, I haven't tried anything like that yet.

By microbevel I mean grinding a tiny bevel at the very edge, different from the larger edge bevel easily visible to the eye.

Check out this picture: http://img75.imageshack.us/my.php?image=img2774pb9.jpg

Where you see the coarse grind marks going up most the blade, that's the edge bevel on this knife (It's sharpened flat to the stone). The tiny bevel at the very edge that is more polished is what I mean by microbevel.

They are useful when you use really thin edges like me, because the edge stays strong while cutting ability is high. But if you just want a regular edge and are sharpening at a more obtuse angle, a microbevel is a bad thing because it's going to serve no functional purpose, the only thing it would do is decrease cutting ability in such a case.

------------------

If anyone in this thread was wondering how to determine how thin an edge should be taken, try this. Take a given knife and consider it's role. Think of the most damaging cutting task you'll subject the edge to on a fairly regular basis. For my Endura 4, that might be doing minor chopping and whittling hardwood. Thin the edge out some, then go do those tasks. If it stands up to it just fine, go a little thinner and repeat. Once you start to see minor edge damage, stop at that angle and add a microbevel, then test again. At this point the edge should hold up with the microbevel and cutting efficiency will be much higher than from factory in most cases.
 
dalee and Vivi, thanks for the additional information. It took me many months to pick up the proper techniques to get that hair popping edge. The magic marker thing was like training wheels, then after following Nozh's video's over and over I finally GOT IT right. I don't think I am ready for a compound edge yet though, maybe someday.
 
if you have a lansky sharpening system or the smiths system (or any other with a guide rod and an arm which has holes pre-drilled to give angles), you can get a very close guess to the angle of the blade by putting it into a hole, and making a small stroke or two on the edge, and then seeing where the marks are. If it's on the edge, the angle is too steep. If it's up higher on the blade, it's too shallow. If it's across the entire edge, you've got it right. I usually sharpen my pocket knife to 15 degrees, but sometimes i do 15 degrees and then put a second bevel that covers around half of the 15 degree edge on it at 20 to help keep it sharp longer.

I'm no professional, but that's what i use. It works fine for me. Also, if you use a hard leather pad and strope it, it maintains a much sharper edge better.
 
It seems that there are many smart innovative ideas on how to measure the edge if you do not have scientific calipers. Did anyone know what angle surgical scalpels are sharpened at?
 
dalee100 said:
Hi,

As you've learned, common tools like protractors are next to worthless. To be able to measure that small, you need to magnify the part you want to measure and then you need the correct scales. I personally would use an optical comparator. An inspection tool that can be had for $2000 to $10,000, depending on how big and fancy. And even then it wouldn't mean a whole lot as even new from the factory, the angle will change from run to run. Even shift to shift and operator to operator.

So, don't get so hung up on exact angles. There really isn't that much difference you can notice in the real world. No commercial sharpener ever made will provide for an exact angle. If they can hit within a couple of degrees either side for the marked angle, consider yourself lucky. Well, I could make it happen but it would require a surface grinder, sine bar, and a set of gage blocks, (and it STILL wouldn't be perfect. Just really, really close). And when you start free-handing, exact angles will mean even less.

If you want to match the factory angle, use the black marker technique as mentioned above. It's fast and easy to do. If you don't like angle, sharpen shallower for easier slicing, but less strength, or more obtuse for a stronger but not as good slicing edge. Experience will teach you what is best for you. Since we all use our knives a bit differently.

So relax, spend less time obsessing, and more time trying. And soon you'll have your knives so sharp they'll cut you if you just look at them wrong.:D

dalee
Click to expand...


Oh my GAWD, Dude! No way! I can't believe this is the first thread I open after just reading this: http://www.xs4all.nl/~jcdverha/scijokes/8.html#might.be_6 :D:D


You can get a quick 'n' good 'nuff idea of the angle thusly:
Take the distance from the center of the spine to the stone, divided by the blade's width. Multiply that result by 58. Viola!
 
Welcome!

Dog of War said:
How to determine edge angle, if you have a caliper:

http://www.bladeforums.com/forums/showpost.php?p=4904824&postcount=77
Click to expand...

Nice - Great for a flat edge, will be some guessing for a convex edge.

Here is the fanciest method for quantifying the edge angle - really would not be that hard to make yourself once you figure out the geometry (that might take longer than making it).

http://www.catra.org/pages/products/kniveslevel1/lglm.htm

And I'll chop wood all day with a 15 - 20 degree per side edge - but keep it away from rocks & dirt! :eek:
 
Broos said:
Here is the fanciest method for quantifying the edge angle - really would not be that hard to make yourself once you figure out the geometry (that might take longer than making it).

http://www.catra.org/pages/products/kniveslevel1/lglm.htm

And I'll chop wood all day with a 15 - 20 degree per side edge - but keep it away from rocks & dirt! :eek:
Click to expand...
It would be interesting to see a goniometer (sounds sort of like a social disease, doesn't it? :) ) used on a convex edge, I assume the beam would be dispersed broadly to reflect the variance in angle across the width of the edge measured.

I like 12 deg./side for my large chopping blades ... and definitely avoid rocks and dirt! With a 20 deg. microbevel they hold up well if the steel's decent.
 
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