I have a 5" long, 1/4" thick fixed blade knife from a well known maker that has basically no edge whatsoever. It doesn't cut paper or cardboard very well at all. I've spoken to the maker on the phone, and even sent it back for re-sharpening. Before I ask for my money back, is their another way to test the sharpness? He has told me that you don't really want it hair shaving sharp because the edge breaks down quicker. None of my other knives are anything like this.
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How do you gage the sharpness of a blade?
- Thread starter Greg Clem
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I sharpen all my knives on my variable speed grinder using a very fine belt. After both sides of the cutting edge are uniform I either use a leather strop with compound or a buffing wheel. I can feel when the strop or buff has done it's job, this part is hard to explain!! At this point I examine the edge with a stereo microscope. Not an expensive piece of equipment, I bought it at a yard sale for $25. If I see no burrs and the cutting egde looks sharp, it is sharp!
SCARRY SHARP!! Combined with my heat treating, they will stay sharp.
I see no reason why a heavy duty knife with a thick edge should not shave hair! I would suggest that you ask the maker to thin the edge slightly because you want it easier to sharpen. If he is as well respected as you say, I'm sure he would do this for you.
Neil
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SCARRY SHARP!! Combined with my heat treating, they will stay sharp.
I see no reason why a heavy duty knife with a thick edge should not shave hair! I would suggest that you ask the maker to thin the edge slightly because you want it easier to sharpen. If he is as well respected as you say, I'm sure he would do this for you.
Neil
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Just updated 10/31!! New Knives, New Pics!!!
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A working edge that does'nt shave is pretty common to me .I like a course edge and rarely sharpen mine to a shaving sharp edge.The bit about not cutting paper or cardboard is out of line.A course edge should shred thru those materials.Sounds like the edge may be to thick.
scott w
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Greg, Is the blade hollow ground, flat ground, or saber ground?
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Gollnick
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"Shaving sharp", "hair poppin' sharp", "scary sharp".... come on people.
If I asked you how long a knife is, you'd say, 7.65 Inches, or something like that. If I asked another person to measure the same knife, they should reach the same number within measurement errors. We don't say, "reasonably long", or "really long," or "scary long." We have standard units of measure and simple, repeatable techniques for making those measurments.
Let's get technical here. There must be some more quantitative, less qualatative way to measure the sharpness of a edge. What is the SI unit for sharpness of an edge? There must be a standard instrument and technique for making these measurements.
When we talk about the hardness of the steel, we don't say, "really hard", or "scary hard." We measure it with test equipment and report it in Rockwell Hardness units. And if two people measure it on two separate instruments, we expect the same number within reasonable measurment errors.
Consider, for example, if, say, Gerber was going to have a knife made for them by another company and they were then going to put there name on it and sell it as a Gerber knife (they do a lot of this, but other companies do too.). They would specify the length in inches or meters as part of the contract and when they received the finished goods, they would measure them to be sure they were within acceptible bounds. They would specify the hardness in Rockwell units as part of the contract and when they received the finished goods, they would measure them to be sure they were within acceptible bounds. If a question comes up, if Gerber's test shows the steel not hard enough, but the vendor's test shows that it is, then an independent lab could make tests and settle the matter. But how do they specify the sharpness? You can't put "scary sharp" in a legal contract. There's no way to test for "shaving sharp."
There's just gotta be a standard unit and standard tests.
What are they?
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Chuck
Balisongs -- because it don't mean a thing if it ain't got that swing!
http://www.4cs.net/~gollnick
If I asked you how long a knife is, you'd say, 7.65 Inches, or something like that. If I asked another person to measure the same knife, they should reach the same number within measurement errors. We don't say, "reasonably long", or "really long," or "scary long." We have standard units of measure and simple, repeatable techniques for making those measurments.
Let's get technical here. There must be some more quantitative, less qualatative way to measure the sharpness of a edge. What is the SI unit for sharpness of an edge? There must be a standard instrument and technique for making these measurements.
When we talk about the hardness of the steel, we don't say, "really hard", or "scary hard." We measure it with test equipment and report it in Rockwell Hardness units. And if two people measure it on two separate instruments, we expect the same number within reasonable measurment errors.
Consider, for example, if, say, Gerber was going to have a knife made for them by another company and they were then going to put there name on it and sell it as a Gerber knife (they do a lot of this, but other companies do too.). They would specify the length in inches or meters as part of the contract and when they received the finished goods, they would measure them to be sure they were within acceptible bounds. They would specify the hardness in Rockwell units as part of the contract and when they received the finished goods, they would measure them to be sure they were within acceptible bounds. If a question comes up, if Gerber's test shows the steel not hard enough, but the vendor's test shows that it is, then an independent lab could make tests and settle the matter. But how do they specify the sharpness? You can't put "scary sharp" in a legal contract. There's no way to test for "shaving sharp."
There's just gotta be a standard unit and standard tests.
What are they?
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Chuck
Balisongs -- because it don't mean a thing if it ain't got that swing!
http://www.4cs.net/~gollnick
I like the direction Chuck is going in, I really have no idea how to do it. This is my first thought. SC (sharpness course scale) from 1 to 10 with 10 being the best. This would judge slicing/draw cuts.
SF (sharpness fine scale) this would rate push/zipper cutting.
SF (sharpness fine scale) this would rate push/zipper cutting.
The problem here is in defining sharpness. I wonder if we can really define "sharpness." A knife is really sharp if it cuts quickly and effectively, but WHAT it cuts figures into our sense of sharpness. And how a knife cuts through something quickly is not only determined by the "sharpness" of the edge but blade geometry as well. For instance, some knives can be "scary sharp" but not very effective at cutting up meat. A good meat cutting knife might not be the best knife for hacking points on tent stakes or chopping through rope. Etc. etc.
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Hoodoo
Cogita tute
[This message has been edited by Hoodoo (edited 01 November 1999).]
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Hoodoo
Cogita tute
[This message has been edited by Hoodoo (edited 01 November 1999).]
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While it would be nice if there were a commonly available way of measuring the sharpness of a knife numerically, there isn't. Not only isn't there a cheap instrument, there is a also the issue of "sharp for what application?". The knife manufacturers who really care about sharpness use Catra testers to cut standard card stock and measure the resistance. I don't know of any Catra testers locally and I'm in the second largest city in my state.
I guess one of the better ways is to indicate how it performs on some easily reproduceable tasks. If you give the edge multiple scores in different application areas it is more useful than trying to lump the numbers together.
Now the problem is how to get "numbers" out of your tests. For most tests you probably want to measure the drag on the blade as you cut through test material. I've played with calibrating tests and this is still something that I would find hard to setup. If you fixture knives so that you can measure forces on them as you drag them through material it will be hard to hold various types in just the right position to get comparable results. If you don't do it right you might launch a razor sharp knife across a room when some spring-loaded scale gadget comes loose. The better way would be to clamp knives in a vice and use a force measuring device to draw test materials across the blades. This I'll leave for further discussion at a later date.
Back to your actual problem of convincing yourself or a knife vender that an edge is good or bad. Find yourself a known good knife (or typical knife) from another vender with relatively equivalent edge geometry. (Borrow from a friend if necessary) Take some reasonably consistent materials and alternate cutting them with the two knives. For example you might try slicing sheets of 20-pound bond paper, cardboard, whittling on 1x4" pine, slicing a beef roast, slicing old leather belts etc. What you want to know is not just that the edges will cut equally cleanly, but also the relative hand pressure it takes with the different knives. If you can say that it takes 2x or 3x as much pressure to cut meat or cardboard with your "bad" knife than it takes to do the job with competitor "X's" knife and furthermore your bad knife shredded the test material...your case is made.
Personally I don't care about factory edge sharpness at all. I sharpen the knife to see how fine a shaving-edge I can get with it. This is how I evaluate the hardness and grain structure of the steel. Then I decide what type of finish to put on the edge depending on application. For most applications I subsequently slightly roughen the edge with a fine to extra-fine diamond stone. If it's really bad steel that wouldn't take a real razor edge, I finish it with a medium grit diamond stone. If the blade is thick and has a thick taper to the edge I also use a medium grit diamond stone.
I guess one of the better ways is to indicate how it performs on some easily reproduceable tasks. If you give the edge multiple scores in different application areas it is more useful than trying to lump the numbers together.
Now the problem is how to get "numbers" out of your tests. For most tests you probably want to measure the drag on the blade as you cut through test material. I've played with calibrating tests and this is still something that I would find hard to setup. If you fixture knives so that you can measure forces on them as you drag them through material it will be hard to hold various types in just the right position to get comparable results. If you don't do it right you might launch a razor sharp knife across a room when some spring-loaded scale gadget comes loose. The better way would be to clamp knives in a vice and use a force measuring device to draw test materials across the blades. This I'll leave for further discussion at a later date.
Back to your actual problem of convincing yourself or a knife vender that an edge is good or bad. Find yourself a known good knife (or typical knife) from another vender with relatively equivalent edge geometry. (Borrow from a friend if necessary) Take some reasonably consistent materials and alternate cutting them with the two knives. For example you might try slicing sheets of 20-pound bond paper, cardboard, whittling on 1x4" pine, slicing a beef roast, slicing old leather belts etc. What you want to know is not just that the edges will cut equally cleanly, but also the relative hand pressure it takes with the different knives. If you can say that it takes 2x or 3x as much pressure to cut meat or cardboard with your "bad" knife than it takes to do the job with competitor "X's" knife and furthermore your bad knife shredded the test material...your case is made.
Personally I don't care about factory edge sharpness at all. I sharpen the knife to see how fine a shaving-edge I can get with it. This is how I evaluate the hardness and grain structure of the steel. Then I decide what type of finish to put on the edge depending on application. For most applications I subsequently slightly roughen the edge with a fine to extra-fine diamond stone. If it's really bad steel that wouldn't take a real razor edge, I finish it with a medium grit diamond stone. If the blade is thick and has a thick taper to the edge I also use a medium grit diamond stone.
These days, I usually rough-check an edge using the fingernail test, mentioned in this forum. The vertical knife edge resting on my thumbnail (angled at about 45 deg) shouldn't slide off. If it does, it's dull.
This is roughly the test done using the Edge Tester from Razor-Edge Systems, but fingernails are more commonly available.
The next test, if I care to do so, is to see how well it cuts paper.
Neither test is intended to be used as a benchmark, it just tells me the general state of the edge. I agree with Gollnick and others that serious benchmarking needs more serious methodology, such as Jeff suggests.
But I'd think the nail and paper tests should suffice to tell you if your edge is sharp enough for most general purposes.
This is roughly the test done using the Edge Tester from Razor-Edge Systems, but fingernails are more commonly available.
The next test, if I care to do so, is to see how well it cuts paper.
Neither test is intended to be used as a benchmark, it just tells me the general state of the edge. I agree with Gollnick and others that serious benchmarking needs more serious methodology, such as Jeff suggests.
But I'd think the nail and paper tests should suffice to tell you if your edge is sharp enough for most general purposes.
Short of using a special piece of test equipment like the Catra that was mentioned I think that visual examination with some stated level of magnification allows one to make statements about a minimum level of sharpness. A knife could actually cut better than expected but it shouldn't cut worse, edge holding and geometry aside. I seem to recall that visual examination with 25x was used in the Scientific American article on T. rex teeth, where serrated vs plain edges were compared.
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Optical inspection is useful. I simply look straight at my edge line when I'm sharpening to see how far I have to go on my rough stone. On the other hand I've taught some science classes and have magnifying tools around. Lots of people don't have these on hand. It is also hard to examine a shiny edge.
A bigger issue to me is that you aren't measuring cutting ability when you just look at edge dimensions. There are grain structure issues that can make a rather coarse edge cut better than a fine edge. The Boye dendritic 440C blades are an example of this. I think that is one of the reasons that people have recently been denigrating the usefulness of oil on hones. You get a smoother edge on a dry stone as it loads up, but it doesn't cut better because of that smoothness. It is really better to do test cutting to test sharpness.
[This message has been edited by Jeff Clark (edited 01 November 1999).]
A bigger issue to me is that you aren't measuring cutting ability when you just look at edge dimensions. There are grain structure issues that can make a rather coarse edge cut better than a fine edge. The Boye dendritic 440C blades are an example of this. I think that is one of the reasons that people have recently been denigrating the usefulness of oil on hones. You get a smoother edge on a dry stone as it loads up, but it doesn't cut better because of that smoothness. It is really better to do test cutting to test sharpness.
[This message has been edited by Jeff Clark (edited 01 November 1999).]
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I lightly rub my finger across the blade perpendicular to the edge. If it bites into my skin, its sharp. You will know when you get there, you just gotta have the feel for it. When its this sharp, with one swipe it will cleanly shave off all hair. CPM440V blades seem to accomplish this easily and M2 also does it well. Good ATS34, 154CM and BG42 will do this too but not as easily as the others in my opinion. I use crock sticks or a Spyderco Sharpmaker to achieve this. YMMV.
I agree that visual examination won't tell much about cutting ability but I think that it does about sharpness, which I consider different than cutting ability. I'd tend to consider cutting ability to be determined by geometry, material, heat treatment, type of sharpening, as well as sharpness, while sharpness is just how well the two edges form an edge. A knife could have a very sharp edge that doesn't cut some things very well.
Gary W. Graley
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I have a friend that brought his Cold Steel Khukri in for me to look at, the edge was very thick, thicker than I would normally use on a knife, but when I tried to shave hair off my arm, an annoying habit my wife hates, it did so surprisingly well! I couldn't believe it! and it did chop well, so you should be able to get almost any knife razor sharp.
What kind of steel is in your blade?
I also do the fingernail test, and for a really sharp knife, I see if it can slice toilet tissue paper, it's gotta be pretty darn sharp to slice those soft fibers without tearing the paper!
Another `Test' I heard was that the person would reach behind his head and see if the edge would catch on his hair.
Remember, we have the right to BARE arms!
G2
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So don't confuse me with the facts!
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[This message has been edited by Gary W. Graley (edited 02 November 1999).]
What kind of steel is in your blade?
I also do the fingernail test, and for a really sharp knife, I see if it can slice toilet tissue paper, it's gotta be pretty darn sharp to slice those soft fibers without tearing the paper!
Another `Test' I heard was that the person would reach behind his head and see if the edge would catch on his hair.
Remember, we have the right to BARE arms!
G2
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My mind is made up,
So don't confuse me with the facts!
www.geocities.com/Yosemite/Cabin/7306/blades.html
[This message has been edited by Gary W. Graley (edited 02 November 1999).]
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If the Cold Steel Kukri was not stainless I would guess it was Carbon V. This is a Vanadium steel like 50100-B. It has a fine grain structure and gets really sharp. Being non-stainless it is extra tough.
Cliff Stamp
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Glen :
All my heavy choppers have shaving sharp edges. In actual fact, assuming the bevels meet. A coarse edge will break down quicker than a polished one, assuming similar levels of work.
Regarding, testing it, take a strip of cardboard and lay it edge wise across your knee. See how far out along it you can cut it before the cardboard bends under the force of the blade. The further out you can go the better the edge geometry and sharpness of the blade.
You can test polished and coarse edges in this manner by varying the stroke used.
-Cliff
[This message has been edited by Cliff Stamp (edited 02 November 1999).]
All my heavy choppers have shaving sharp edges. In actual fact, assuming the bevels meet. A coarse edge will break down quicker than a polished one, assuming similar levels of work.
Regarding, testing it, take a strip of cardboard and lay it edge wise across your knee. See how far out along it you can cut it before the cardboard bends under the force of the blade. The further out you can go the better the edge geometry and sharpness of the blade.
You can test polished and coarse edges in this manner by varying the stroke used.
-Cliff
[This message has been edited by Cliff Stamp (edited 02 November 1999).]
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Hollow ground 1095 should produce an excellent edge if sufficiently honed. You may not really be reaching the final edge with your ceramic rods. Try using a coarse or medium-coarse large aluminum oxide bench stone or large diamond plate at about 20-degrees per side. You should be able to get a decent cutting edge on any carbon steel (sometimes a really bad stainless is so full of lumpy carbides that you can't get a reasonable edge). You may need to apply more pressure and work longer than you expect. Work on just one side of the blade till you can feel a burr starting to form on the opposite side of the edge. If you don't feel the burr you just aren't sharpening hard and long enough. 1095 feels different from some steels. When it's hard it can feel kind of glassy when honed. It feels like it's sliding over the hone without being cut. Just keep going. Hold your honing angle consistently as you work.
It would be hard for the blade manufacturer to do anything so wrong to 1095 that you couldn't get a sharp edge on it. If they left it too hard, like a file, it would be hard to sharpen and the edge would chip when you used it. Never the less you could temporarily get it sharp. If they left the steel too soft you would easily get it sharp, but it would dull very rapidly.
It sounds like this knife is on the hard side. Just try sharpening harder.
It would be hard for the blade manufacturer to do anything so wrong to 1095 that you couldn't get a sharp edge on it. If they left it too hard, like a file, it would be hard to sharpen and the edge would chip when you used it. Never the less you could temporarily get it sharp. If they left the steel too soft you would easily get it sharp, but it would dull very rapidly.
It sounds like this knife is on the hard side. Just try sharpening harder.