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 Post subject: The Sharpness test I've been waiting....DONE!
PostPosted: Thu Oct 15, 2015 7:17 am 

Joined: Wed Feb 11, 2015 2:15 am
Posts: 212
Edge Sharpness test

After reading so many different theories, sharing different points of views, trying to figure out what would be the best finish on the edge for the tasks on this and that knife, selecting the correct sharpening stones and spending hours mixing and playing with our stones, strops, techniques etc etc etc …… I decided to make my own conclusions about what would be the best as an all-around edge for my every day carry (EDC) blades between three different edge finishes using the same knife brand, model, steel, sharpening angle and cutting tests. For this test I’m using 3 different Spyderco Paramilitary 2, all with CPM S30V steel.

The knives where sharpened as follows:
1. Black G10 and Satin blade (knife #1) was sharpened 100% on the Edge Pro Apex setting the angle at approximately 17 degrees per side. I used the 5 stock stones plus the 3 polishing tapes which based on an email from Mr. Ben Dale (inventor of the EPA) the last polishing tape is 0.5 micron. Then I strop the knife on the EPA using a Kangaroo leather strop loaded with Ken’s CBN 0.5 Micron spray. This will represent a very high polished edge.

2. Black on Black Paramili 2 (knife #2) was sharpened again using the Edge Pro Apex. The angle used was exactly the same as the first Para 2, both knives where sharpened one after the other so the angle is 17 degrees per side as well. This knife was sharpened using only the first 3 Edge Pro stock stones (120/220/400). The last stone was used as if it was a strop doing only edge trailing strokes until all marks from the previous stone where gone. This knife will represent a toothy edge. I decided to finish the knife on the 400 grit stone as this will be between the Shapton 1K and the Shapton 2K according to the Uni Grit Chart. Most people like the 2K edge and others prefer the 1K edge based on the things read on the Chef Knives to go forum so an in between edge was the way to go here.

3. Digicam G10 and Black blade Para 2 (knife #3) was sharpened using the Edge Pro Apex AND freehand sharpening and this is how it goes. The knife had the stock edge on it so I kept the same angle on the EPA after sharpening the first two Paramilitaries and used only the 120 grit stone to set the same angle on the knife. (I used the drill stop collar so it’s a fair test) Then I went to my Japanese Waterstones and used the King Deluxe 1000 grit stone with only edge trailing strokes to set a 1K edge erasing all the marks from the 120 stone (This was no problem at all). This was done in order to test the King Stone as many say it’s a slow cutter on hard steel but let me tell you that the stone even thoe I was using the stone as a “strop”, the steel was being removed quickly without dishing. I took my time to try to keep the angle as clean as possible and I think I managed to. After rising o burr I switch to the other side and clean the edge, removed the burr etc etc etc (don’t want to go into detail with sharpening process) and then I finished the knife on the King Super Fine S1 6000 grit stone. Straight to the point I used exactly the same technique Murray Carter (MC) uses when sharpening a knife which is the way I sharpen my knives because I love this technique, it’s cheap, effective, quick and is more than proven by a master blade smith. I didn’t over polish the edge on the 6K. I took the same amount of strokes MC takes when using the 6K stone. Then I finished the edge by stropping it on a piece of news paper on top of the 6K stone. This knife will represent obviously Murray Carters Technique which I consider to be a middle edge between a toothy and a polished edge using the “hated” King stones which I love.

Before going into detail with the cutting test I want to mention that I will try to be as fair as possible here, I’m not trying to defend a technique or a specific edge finish, I really want to know what could be the best possible edge finish for a knife that will be used as an EDC knife and I’m doing this to have my own conclusions about the famous battle between Toothy and Polished edges. Maybe there are better ways to test this but then I invite you to do your own test and share it with all of us please.

Cutting Test
• Tree top shaving test: Shave hairs without touching the skin.
• Leg hair shaving test: Regular shave trying to see if the edge leaves a few hairs behind its path.
• Tomato skin cut: See if there really is a big difference between the edges when trying to cut the skin on the tomato. Sometimes a very high polished edge with RUN through the skin of the vegetables and then cut them and a toothy edge will go straight into cutting. I used just the weight of the knife to do this holding it with just to fingers.
• Tomato slicing without touching the tomato trying to cut it as thin as possible.
• Newspaper push cut test:
• Newspaper slicing cut:
• Meat cutting: See if there really was an advantage of the toothy edge when cutting proteins.
• Cardboard cutting.
• Manila rope cutting.
• Nylon rope cutting.
• 550 Para cord cutting: Resting the knife with the edge towards the roof I tried to count how many times where needed to cut the 550 Para cord moving it back and forth with in a 1 inch displacement.
• UTP computers cable with 7 small cables inside with copper.
• Plastic bottle cut in half.
• Printing paper test.
• Phonebook paper test.
• Newspaper test.
• Wood feather sticks.

To measure the results of the different tests, I will just try to see by using the three different types of papers above, which edge started to fail first or started to show more resistance when cutting through the different materials.

What I was expecting to happen before the cutting test:
CPM S30V steel is fairly hard and will take me to long to completely destroy all 3 edges but I would expect all three blades to lose their keen shaving sharp edge fairly quickly and get into a “toothy working edge” mode and hold it for quite a long time (that’s why I love S30V steel) so I will figure out which blade goes into this stage first. The toothy working edge I’m expecting to get at a microscopic level is an edge formed by all those little carbides found in this steel forming little teeth which sticking out and are very hard, this teeth’s will not dull un less you grind them out or you tear them apart by cutting on really hard surfaces or by abrading the edge of the knife with something harder than the carbides like diamonds.

Results of every test in the same order they were done:
• Tree top shaving test:
Knife #1 had no problem at all with its polished edge, it cut the hairs very easy and you could even hear them no problem. Knife #2 I could only feel like 4 time the hairs being cut or pulled, not even close to easily cut the hairs, I won’t say it didn’t cut the hairs at all but it was close to none. Knife #3 with its semi polished edge did almost as good as the polished edge, we could say a 100 to 80 comparison, you could feel and hear the hairs being cut but when checking the white printer paper there where not as much hairs as with knife #1 but it was very close.
Winner: 1-3-2
• Leg hair shaving test:
All three knives performed extremely well by not leaving any hairs behind its path but there was a different feeling and sound between the knives being this a more aggressive feel and a louder tearing sound as the blade increased its toothiest so I will call this a tie in terms of performance but a smoother feel and sound for the knives with a more polished edge. (1-3-2)

• Tomato skin cut:
Knife #1 didn´t very well, it did cut the skin with no problem meaning that there was no “running of the edge” along the skin of the tomato but the blade didn´t penetrated too much, only like 2mm deep. This means that with a little more pressure instead of using just the weight of the blade, the knife will cut the tomato with no problem at all (at the end of the test I tried this and in fact no problem cutting the tomato using the weight of your hand). Knife #2 showed a big difference with almost double of penetration into the cut 4mm. You could actually feel the teeth’s of the edge cutting like three times more aggressive than the polished edge but on the other hand it did showed just a little more damage on the cells of the tomato, its rougher edge did tear apart just a little more. Knife #3 cut way cleaner than knife #2 and was twice aggressive than knife #1. The difference in deepness between knives #1 and #2 was almost imperceptible.
Winner: 2-3-1

• Tomato slicing without touching the tomato trying to cut it as thin as possible:
This test was easy to conclude as the more polished the edge, the easier it was to cut the thin slices of tomato. If the edge had too much micro teeth’s it felt like a lot of resistance was putted into the cut and felt like if you were pushing the tomato and not much cutting it. A polished edge is the winner for this test.
Winner: 1-3-2
• Newspaper push cut test:
All three knives passed this test with no problem at all. The main difference was that the toothier the edge, the louder it sounded while cutting and more micro hairs of paper where exposed in the cut. The polished edge left a cleaner cut but again in terms of performance all three knives did equal.
Winner: Tie
Smoothness: 1-3-2
• Newspaper slicing cut:
Exactly the same as before.
All three knives passed this test with no problem at all. The main difference was that the toothier the edge, the louder it sounded while cutting and more micro hairs of paper where exposed in the cut. The polished edge left a cleaner cut but again in terms of performance all three knives did equal.
Winner: Tie
• Smoothness: 1-3-2
• 550 Para cord cutting:
Here was where the toothy edge started to shine. Knife #1 with its high polished edge needed 15 passes along the edge to cut the Para cord while knife #2 needed only 2. You could feel a big difference on how quick and aggressive the micro serrations on the edge where cutting the cord with no problem at all. Knife #3 performed exactly the same as knife #2. Its semi polished edge had enough teeth’s to be able to cut the cord as fast and with a more smooth feeling than knife #2.
Winner: Tie between knives #2 and #3

• Meat cutting:
Knife #1 didn’t manage to completely cut the chicken in one pass, it cut only half way. Knife #2 was way more aggressive where you could even feel the edge sticking into to cutting board while passing through the chicken cutting it 98%. Knife #3 performed not as good as the toothy edge on knife #2 but way better than the polished edge on knife #1. It was a decent cut 70%.
Winner: 2-3-1
• Cardboard cutting:
First 60 cuts with each knife.
The higher the polish on the edge the less resistance you could feel during the cuts. This where done with a combination of a push and slice cut if you know what I mean, If not go try and cut some cardboard and you’ll see for yourself.
Winner: 1-3-2
After 120 cut with each knife.
Again the polished edge showed less resistance along the cuts.
Winner: 1-3-2
After 150 cuts with each knife.
When finished the cutting session, I tested the knives on newspaper and you could start to see and feel that the polished edge was starting to lose its keen edge and was adopting more of a toothy edge, still offering less resistance that the other knives BUT was the first knife to show deterioration on sharpness.
Winner: 3-2-1
Smooth and easy of cuts: 1-3-2

• Manila rope cutting:
The rope cut test helped to increase the edge damage on the knives. After making 150 cuts with each knife in a complete forward and back motion, I noticed that the polished edge started to suffer a bit more but still cutting the rope like if it was nobody’s business. When the rope was cut in a forward motion it was easier for the polished edge to make the cut but if you tried to cut the rope in a backwards motion, trying to use the teeth’s on the edge, it was a lot more difficult, actually not effective. The semi polished edge on Knife #3 didn´t had this problem, it was cutting the rope extremely easy in both directions and felt very nice. Knife #2 cut the rope very well but it´s excess of toothines actually made it a bit more difficult and uncomfortable to make the cut than knife #3. You could feel the teeth’s sticking into the ropes fibers but once you break this resistance it went and cut the rope no problem.
Winner: 3-2-1
We teste the knives on newspaper after this test and notice that knife #1 completely lose its keen edge as well as knife #3 but it felt nicer due to its little teeth’s doing the job.

• UTP computers cable with 7 small cables inside with copper:
We did 20 cuts on this computer cable and notice that the polished edge started to show even more the little damage on the edge. We could feel this by running the tip of the nail on the edge and feeling all the imperfections. On the toothier edges you could feel some imperfection but a lot less pronounciated.
All three knives cut the cable no problem.
• Manila rope cutting:
We did 60 more cuts on this type of rope.
Knife #1 entered in a toothy edge mode and was cutting the rope no problem. Knife #2 cut the rope with no problem, still showing the feel of sticky tooth edge on the rope fibers, I don’t know at this point of the toothy edge was enhanced at this point due to the deformation on the tips of the serrations. Knife #3 lose its keen edge but again cut the rope very easy and with a nicer feeling than Knife #2.
Winner: 2-3-1
• Plastic bottle cut in half:
In this test we could only notice that the polished edge sliced a little smoother than the toothier edges but all three knives did equal.
Winner: Tie
• Wood feather sticks:
This was easy to make a conclusion. The more polished the edge, the easier it was to cut the wood. The toothy edge felt like sticking too much into the wood as the polished edge felt like just shaving of the small pieces of wood.
Winner: 1-3-2

• Printing paper test: No problem with any of the three knives after the tests.
• Phonebook paper test: No problem with any of the three knives after the tests.
• Newspaper test: No problem with any of the three knives after the tests but I could felt the deterioration of the edge in the polished knife #1. It felt like it started to be a lot rougher on the paper and didn’t cut it as smooth as before. Knife #2 felt a lot more aggressive but could actually cut the paper very nice and clean. Knife #3 did the same as knife #2 but just with a little more of a smooth feel to it meaning it could be a better edge on this paper at this stage.
After hours of using all three knives cutting different materials, I will dare to say that some theories are proved and some are not. Again using hard steel for this test made it difficult for me to decide what could be the best all-around edge for an EDC folding knife. There is no doubt that the polished edge performed very well on all the tests but this level of refinement is definitely meant to be used on push cuts like shaving or making feather sticks. It was indeed the first type of finish to show some sort of deterioration on the edge entering itself in a more toothy edge that feels will last a lot at a sacrifice of not performing very well on tasks where some sort of teeth’s are needed.

The toothy edge from knife #2 performed very well on all tests and didn’t show a lot of deterioration on the edge compared with what we started, it kept that toothy feeling all the time by just increasing its roughness along the test but not letting this affect its performance too much. What I didn’t like about this edge was that sometimes too much grip or too much teeth’s makes the cutting task a bit more difficult showing more resistance through the materials making you to need to push a bit harder and this can be very uncomfortable. It also shine a lot more on slicing motion cuts and failed more in push cuts.

The semi polished edge on Knife #3 from Murray Carters technique was for me….. here we go…. THE BEST ALL AROUND EDGE FOR A FOLDER. The reason is that this edge performed extremely well on every task, comfortable feeling, smooth cuts, just about enough roughness on the edge, the perfect combination for a push and slice cut and at the end it was the edge that managed to cut newspaper better.

This means that there must be a balance between the aggressiveness of the edges teeth’s and the level of refinement of this teeth’s. A very aggressive edge wont perform very well because you need refinement to help you perform some tasks better and a very high polished edge will fail in a lot of everyday tasks because you need a little of aggressive teeth’s on the edge to make the cuts through materials easier.

The best edge for me would be a good combination between polish and coarseness and this is not easy to do. This will vary between knives and steels and angles. You will now need to find which edge finish will perform better on your knife according to most tasks you want it to perform because we all use our knives differently.
If you want to go ahead and experiment with extremely high polished edges, go ahead, you will still cut and cut well and if you want to just use one stone and put a factory coarse edge on your knife, you will still cut very good as well but if you want an edge that will give you the best performance all around (at least in CPM S30V steel with a 17 degree edge) you will need to put a semi polished edge that will last you a lot. I don’t know if the extra time putting a high polished edge on a knife is worth it as it losses its keen edge very fast plus its expensive.

The stone I have found that gives me this type of edges (semi polished) and the one I’m happy with the results on folders and kitchen knives is the Aoto Green Brick of joy 2K stone. This will polish the edge just as mush as needed and will give you a nice toothy feeling to it. Another option is the Shapton Pro 2K finishing with 3/5 passes on a high rit stone like 5K just to refine a little the edge, you can also use a strop with a 2 to 4 micron compound. You can’t go wrong with this stones.

With that being said I would also like to mention that if you really are a knife enthusiast and are into knife sharpening, all three finishes will last way longer than you can resist to touch up the knife’s edge so maybe if you have a very intense sharpening session and you are always watching carefully for you edge then you could maybe go with any edge finish and you’ll be happy. If you have a knife sharpening business I would put on my customers knives a semi polished edge to make them as happy as possible when they use their knives for multipurpose tasks. Depends on how you want to look at it.

"Do you require a smooth razor keenness or a toothier bite? Choosing the right stone and using it at the right time are key in producing a sharp and durable edge for the desired use of the knife"

Sharpening time was not mentioned but it’s obvious that a high polished edge will take a lot more time and maybe this is something some people is not willing to deal with. Costs of the equipment used like the Edge Pro Apex, water stones, strops and CBN emulsions is also something to consider that I didn’t mentioned but this can be all done by hand with just adding more stones to your system. The Edge Pro Apex was used only to make it a fair test by having all 3 knives with the same angle. I also know that a different steel on this type of folding knife can perfectly behave in a more different way but I choose to use the Spyderco Paramilitary 2 in CPM S30V steel for two mayor reasons: First of all its one of my favorite EDC knife out there and its always in my pocket plus I collect them so I had several to use and second I consider that this steel is extremely common on pocket knives now days and we can put it in let say the middle range between low mid steels like AUS8A and Super Premium steels like ELMAX, CTS/XHP, S110V, M390, ZDP/189 in order to get a general conclusion for folding EDC knives.

This test will be done again but using two German Mercer Cutlery Genesis 8” Chef Knife with soft steel to try to put to test both theories about using highly polished edges versus toothy edges on a soft steel kitchen knife and have both sides of the coin figured out as I will supposed that all Japanese Kitchen knives can be taken to a high polished finish with no problem due to the type of steel used and the fact that this knives are only used for cutting food, not near the tasks done by an EDC blade. I will compare a 2K Shapton Pro edge versus a 6000 S1 King Stone finish plus strop. Later to come.

Let me know if you liked this Edge sharpness test and what you think about it based on my results. There are way too many different methods to do this, I tried to make it as fair as possible in order to help out some of us who are still searching for the best overall edge on a knife and I’m very happy I can now make my own conclusions and that I experienced this by myself.

I hope this has been in some way helpful to you and if not, thank you for reading till the end.

Stay safe….stay sharp!

Jon from Edge Craft Costa Rica


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