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Murray Carter "Three Finger Sharpness Test"....what?

Discussion in 'Maintenance, Tinkering & Embellishment' started by Ultimate, Apr 23, 2011.

  1. Ultimate


    Jul 5, 2009
    I held off on making this thread because I figured I just absolutely sucked at sharpening (probably still do!) and that's why his "test" wasn't working.

    For anyone who doesn't know, the three finger edge test is where you place three fingers on your edge and VERY lightly wiggle them back and forth. If your edge is "Murray Carter" sharp, your fingers should feel the edge bite into the pads and prevent you from further wiggling them on the edge.

    Well I tried this test with my knives and it just doesn't work. I can actually slide my fingers across the edge with "somewhat" significant pressure and nothing will happen...

    What I don't understand is, that same edge will glide through paper and shave my arm/leg hair with ease.

    Judging from Murray Carter's test, my edges would be dull. Is there an entire realm of sharpness that I have never experience before? Or is his test a joke? What gives?

    P.S. I use a Sharpmaker and a strop with standard green compound.
  2. vwspdshp


    Sep 20, 2008
    There IS an entire realm of sharpness that you have never experienced!

    I promise. I was a little disappointed when I discovered this too. I use his sharpening method now and get good results on most steels. I still sometimes struggle with some stainless varieties though. To bring them to that point, that is. Remember, this is a "working edge" for Murray, not the sharpest possible!;)
  3. pwet


    Feb 13, 2009
    never managed to make it work, i must lack self preservation instinct or whatever because each time i tried this stupid test i cut myself to blood ...
  4. foxx


    Sep 5, 2010
    You have stropped away the toothy edge. The smoother edge might not bite your skin the same way, but it will cut. I prefer this kind of edge on lots of my knives.
  5. Ultimate


    Jul 5, 2009
    I knew it! What am I doing wrong then? Is it possible to get there with my simple set-up?
  6. Ultimate


    Jul 5, 2009
    If I remember correctly, Murray strops on newspaper. Wouldn't that also smooth out the edge?
  7. vwspdshp


    Sep 20, 2008
    The newspaper refines an already sharp edge just a bit. I don't know if I could get the same result with a sharpmaker as I don't have one. I have gotten similar results with my old Lansky setup, but it takes me longer than using the water stones. Murray's sharpening technique DVDs have plenty of helpful info, and he covers the sharpmaker in one of them. Just a comparison to his method though.
  8. Battle Creek Knives

    Battle Creek Knives

    Feb 23, 2010
    wow I've never heard him or don't ever remember MC talking about the 3 finger deal, sure its been a while since I've seen any vids but,:eek: WOW !!!

    there obviously is a level of sharpness neither of us have experienced, I understand it to be a geometry thing and has noting to do with slicing paper etc..

    look at RichardJ he cuts toilet paper in half, and newspaper held way far down at the corner, goes through like butter.. I have yet to achieve this 'level' of sharpness........

    this thread is sure to make me crazy now........
  9. unit


    Nov 22, 2009
    Well, the test is not stupid...it is what it is. Weather the test (as you attempt it) shows you what you desire to learn is another thing.

    Anything that requires a human to feel something and gauge performance based on feel is subjective by definition...and therefore only standardized to the person with digits on the edge.

    I use a variant of this test and have since I was about 5...I feel the test is adequate for identifying an edge that will easily cut flesh vs one that will not...but I think there is a point where this test does the opposite of what is intended.

    To convey this another way, some edges will "bite" as they become sharp and will be identified as such by this test....but then as the edge is refined further the perceived "bite" diminishes and this test will result in one or both of these potential outcomes;
    A. the edge is perceived as not sharp because the tester does not feel any "bite",
    B. The edge separates flesh.

    I have seen this happen. I had a highly polished edge and handed it to a very experienced sharpener and he tested in this manner. He handed the knife back and said, "not bad" in a tone that almost masked his true feelings that the edge was not very sharp....as I took the knife, he realized he was bleeding and said something along the lines of "oops, I guess it was a bit sharper than I thought".

    Based on this, I hesitate to condemn the test because perhaps everyone I have seen use it does not understand how to properly perform it...then again, if it is that hard to perform...it is not very useful (and therefore I do not fault anyone that shuns such a test). Further, I think we need to consider that probably no single test can really tell us what we need to know about an edge (unless that test IS the SINGLE function that the blade performs...but it is sort of rare to use an edge for only one function)

    There are countless ways people gauge edge sharpness...and several theories on polish vs toothy. The only thing I THINK I know is that there are no right answers...there are only tools that work for you and your preferences. In order to figure things out you have to be open to trying what you presume might not work...sometimes you will be surprised, other times not...

    Have fun.
    Last edited: Apr 24, 2011
  10. Ultimate


    Jul 5, 2009
    Thanks for your replies. I agree with everything that has been said so far, especially what unit said. My question really arises from this: I don't know about other peoples' standards, but for me, I do not consider my edge sharp if I can actually (with some pressure) run my fingers along the edge (the entire length) back and forth without getting cut; even if it can already slice paper and shave. I strive for an edge that will simply split skin if a finger is rested upon the edge and pressure is applied. This, I would consider "edge nirvana". At my current skill and equipment level, this is unobtainable. Therefore, my goal at this point is to create an edge where I CAN'T rub my fingers along the edge without it cutting into my skin. I feel that if the edge is sharp enough (polished or not) you should not be able to rub your fingers along the edge while applying some pressure.
  11. unit


    Nov 22, 2009

    Let me point something out that you perhaps already understand (with an example)

    Go work in the farm field and fail to bring along any fluids...get your body nice and parched so the callouses on your fingers are like dry shoe leather and try your test.


    Go soak in a hot tub for 15 minutes and try your test again (same edge)....

    Another test I (and many others) like is to shave arm hair. As an edge gets more and more refined it will shave with less and less pressure until no pressure is required at all. This is commonly called "tree topping"...and there actually is pressure but it is consistent with the stiffness of the hair...if the edge is not sharp enough the hair bends out of the way instead of cutting. Again, this test is subjective because all hair is different and moisture content is a critical factor...But one reason I like it is, I can test many portions of the edge independently to gauge relative uniformity.

    I maintain that there really needs to be several tests used by each sharpener and they ought to be use-specific. I generally will use my thumb pad (like Murray's test), shave some hair, cut some paper or fabric, and whittle some wood (this generally rules out burrs or wire edges). I have produced edges that would do amazing "tricks" (whittle hair, tree top hair, shave print off newspaper, and slice toilet paper) only to have them dull before I can make a single fuzz stick for fire building....that demonstrated to me that my "wonder edge" was actually a really good wire edge...which is crap! Now that I added the additional test, I can ensure that the edge will do it all (or at least all *I* want it to do)!
  12. Ultimate


    Jul 5, 2009
    Yes, I know, and have considered exactly what you described. Problem is, it doesn't matter if I lay brick for a week, or spend a day in the ocean, my hair shaving edges won't ever bite. However, if I only use the Sharpmaker, the edges bite with ease. As we know, that is because the Sharpmaker leaves a toothy edge. That edge will not shave hair as easily as if I strop it though.; and that is what led to my questioning of his "test". He seems to use the newspaper to refine the edge yet still gets it to bite. It would be interesting to send him a knife to have sharpened, and compare it to the same knife that I sharpen using my method.
  13. unit


    Nov 22, 2009
    Yeah, I think you are right.

    It is good to consider the types of steel he is using...some alloys result in a different perceived "bite" even with the same finish (at least they do in my findings...and a few other guys I have talked to).

    Another thing to consider is the disconnect that occurs along the journey of the concept from
    1. what someone feels,
    2. How they describe it (in a video or in text posted on the web), and
    3. How you interpret their description/resentation.

    Getting Murray to finish YOUR knife edge is the only real way for you to experience the difference between what you methods gave, and his. Even if you use his methods, you may not be executing them the same way...

    For being the second most simple tool (next to the hammer) the knife really is a complex beast...
  14. Ultimate


    Jul 5, 2009
    That's for sure!
  15. Steel130

    Steel130 Gold Member Gold Member

    Sep 17, 2010
    I use the sharpmaker, and I can get an edge that I dont even like to put my finger on and move it across the edge without any pressure. I have used this same edge to cut through a pop can over 15 different cuts in various ways and it will still shave hair and push cut paper. To me this is a usable edge and I dont really see why I would need it sharper. But then thats just me. Perhaps I need to hold a knife that will push cut toilet paper though first lol.
  16. BryFry


    Jul 29, 2009
    Hey, am I the only one who when seeing Murery Carter run his three fingers along a razor sharp edge for the first time thought: WTF IS HE DOING?!?

    LOL, I realize now that he is a pro, and it must be working for him, it's just that I was taught from childhood that you NEVER run your fingers down the edge of a blade. I've seen many guys do this test on one of my knives only to slice open their fingers (often badly) and then look at ME like WTF?!?

    Am I the only one who tests an edge by running a thumb or finger ACROSS the edge, NOT along its length? Works for me, when I rake the pad of my thumb across the edge I can feel how sharp it is by how much I feel it catch on my skin. An extemely sharp edge will feel kind of "sticky" and bight right away without much movement at all. And doing it this way there is pretty much no risk of cuttin ones self no matter how sharp the blade is.

    I also find that I can get a pretty good idea of the condition and sharpness of an edge just by looking at it and seeing how the light glints off the very outer most "edge" of the edge. The more glint you see at the very edge the less sharp it is. Ideally you do not want to see any glint that is separate from the rest of the edge, it should appear to be one continuous grind ending in a "zero point" looking edge. I use this method to visually inspect an edge that I am working on, sometimes there will only be one small spot along the edge that needs more work and I can spot it just by looking this way.

    ...Does that make sense to anyone else, or is it just me? :confused:

    Last edited: Apr 24, 2011
  17. unit


    Nov 22, 2009
    BanFry, that sounds about right to me. I generally use the thumb sliding off the side like you say also....even that freaks some people out.

    From a strictly OSHA-type point of view, it is kind of silly to ever put a body part on an edge....but almost all of us do, so...
  18. Ultimate


    Jul 5, 2009
    Your method of running your fingers across the edge (perpendicular) is EXACTLY what I do. (I use my thumb and it's more of a downward rub at an angle using just the tip of the thumb. If the edge is sharp and thin, you can also hear the difference in the sound it makes as it scratches against your skin) I didn't mention it initially because I didn't want to confuse anyone, lol! I get the same results you do, though. Performing this test on my knives will show that the edge is pretty dang sharp, but comparing it to Murray's test would lead one to believe it is as dull as a butter knife. That's why I started the thread.
  19. singularity35


    Mar 1, 2010
    I too, have edges that feel dull with Carter's test. I do polish to 3000 grit tape and strop on green compound. My edges do feel very sticky if you touch them and just apply a very slight diagonal, perpendicular movement and pressure. I can do the tree-topping, TP slicing, hair whittling thing but I do know that I still do not get them as sharp as some others here can. I am curious though what an edge that passes MC's test feels like. I'd also like to say that I have never cut myself touching my edges indicating to me that I have a long way to go in learning how to sharpen.
  20. Allcaps321


    Mar 27, 2011
    I thought his test was to be able to feel your heartbeat at your finger tips when you touch the edge?

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