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Testing how sharp

Discussion in 'Knives' started by Tegan's Dad, May 6, 2014.

  1. bpeezer

    bpeezer Loaded Pockets

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    Also a big fan of the 3 finger test. If it's three finger sticky and leaves tiny superficial cuts, it's usually a pretty good edge.

    [​IMG]
     
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  2. that_stupid_kydd

    that_stupid_kydd Loaded Pockets

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    i like to do the paper test but i use news print if possible, i'm guilty of doing the hair test but only to show off to others :p
     
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  3. SAKplumber
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    SAKplumber EDC Junkie!!!!!

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    My Dad always "pops" the hair off of his knuckles to test. I usually just look straight down on top of the blade and examine it from the side. (V-grind). I only shave arm hair to show it off :D

    I shave paper curls with convex grinds.
     
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  4. IMightBeWrong

    IMightBeWrong Loaded Pockets

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    I really need to stop using the hair test. My arm looks ridiculous.

    And for anybody looking for a good strop, I'd look into Stropman Strops. You can get them with compound at a great price.

    There are a few people out there that present this idea that stropping is detrimental to your edge and that it makes it weaker. I have yet to see them produce proof of this that can be seen rather than theorize about it, skip the testing, and state the theories as fact. The sharpest blades I've witnessed were all stropped. I have yet to encounter a 160,000 grit stone, but you can get a near-equivalent paste for a strop if you really want to go crazy, plus stropping can maintain an edge for a long time without sharpening and removing more metal than the strop would. And even if the strop does ever prove to weaken edges, I'll still use one because it's dead simple and I've watched stropped edges do some amazing cutting without losing their hair-popping edges.

    Just speaking to the anti-stropping argument before it rears it's ugly head.
     
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  5. Massen

    Massen Loaded Pockets

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    1. Visual inspection, using a bright light makes this step easier. I look for any kinda imperfection in the grind, make sure it is even, complete, and consistent.

    2. Feel test. I use my fingers to check for burrs that need to be removed, make sure the edge feels consistent. Finish by making sure it will catch my thumbnail.

    3. Hair or Paper test. Depending on the blade and what I have around I will occasionally use hair to test my edge, but I prefer paper as I can do as others have recommended and listen to the way the blade cuts and inspect the cut. I also prefer paper because it is easier to test the whole length of the blade.

    One thing that always surprises me is the value of a visual inspection. Often if I forget this step and find an issue when feeling the blade I can see the issue visually. Again, the key to this step is a bright light. It is also pretty hard to cut yourself doing a visual inspection. ;)

    - Massen
     
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  6. chrisk91

    chrisk91 Loaded Pockets

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    I use my thumb and see how little pressure it takes for the blade to 'grab'. I've found that knives that aren't all that sharp can still cleanly slice paper. After the thumb test is passed, I go for some hair.
     
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  7. opichocal

    opichocal Loaded Pockets

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    Grab a flashlight and shine it at the edge. If you see a reflection then strop it. Works for me 90% of time


    Sent from my iPad using Tapatalk
     
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  8. thatotherguy

    thatotherguy EDC Junkie!!!!!

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    I just run my thumb across it lightly, perpendicular to the edge. If the edge catches my thumbprint satisfactorily then it's sharp enough.
    For what it's worth... I've been through the spectrum of sharpness. I've used a coarse (probably 600 grit or so) stone as my only stone, I once spent hours hand convexing and mirror polishing a Condor Bushlore edge, and everything in between. I've learned that for most utility purposes, a toothy but sharp edge works best. That mirror polished edge popped hairs like none other, could have stood in for a confetti machine, and looked great. But all that meant nothing when I tried to cut paracord with it and it slipped without cutting cleanly.
    A well executed edge from a Spyderco Sharpmaker or a decently fine stone is a fantastic cutter.
    Oh, and I had a butcher knife I sharpened with a medium coarse stone and nothing else and that thing cut like the dickens. It was an amazing workhorse.
     
    Last edited by thatotherguy, May 10, 2014
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  9. microbe

    microbe EDC Junkie!!!!!

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    I test on newspaper
     
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  10. sbillard

    sbillard Loaded Pockets

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    Thumb nail. If it "bites" the nail, then it is sharp enough.
     
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  11. UCChris

    UCChris Loaded Pockets

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    What do you guys mean by "biting" the thumb nail? I just barely got into sharpening my own knives (like less than a week ago) and I've finally gotten to where I can easily slice paper (I'm freehanding on a diamond rod so it took some practice) but I know that some knives will slice paper when they're not really all that sharp.

    Also, when stropping should you push the knife like it was cutting or drag the edge backwards?
     
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  12. MTFatboy
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    Drag the edge definitely, otherwise you will just cut your strop (and dull your knife). As far as biting the nail, unless a knife is reasonably sharp, if you run the edge down your thumbnail, it will slide. If it bites into the nail instead, especially when you apply no more force than the weight of the blade, it is pretty sharp. A knife that cuts paper isn't necessarily shaving sharp or even nail biting sharp. I wouldn't be able to advise you, though, how sharp you can expect to get with a diamond rod and a strop; in my own experience the more stages using successively finer grinds the better.
     
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  13. Moco

    Moco Loaded Pockets

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    i test it on hair, receipt paper how smoothly it cuts and the sound, and on my thumb nail.
     
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  14. smokingfish

    smokingfish Loaded Pockets

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    For me, I use my fingers. If I feel my skin splitting with feather pressure I know it's sharp.

    Also I'll roll up thin wax paper and cut it, it should slice quietly.

    I am obsessed with sharpness, being a sushi chef and all.
     
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  15. doby34

    doby34 Loaded Pockets

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    A little off topic- I would be very interested in reading a thread about how being a sushi chef has changed either your opinion of what is sharp, and also the proper technique to create an edge suitable for sushi.
     
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  16. MTFatboy
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    I agree; I feel some of the more interesting developments in blade technology recently have been fueled by sushi chefs' need for knives that are non-porous and chemically inert yet sharper than :devil:.
     
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  17. smokingfish

    smokingfish Loaded Pockets

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    Well sushi chefs aren't producing the sharpest knives, they just need them at a certain sharpness (which is above average for sure). But I have seen videos of guys who strop with an assortment of compounds and have some scary sharp edges.
     
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  18. MTFatboy
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    To get the thread back on track: my bald forearm.
    [​IMG]
     
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  19. flatblackcapo

    flatblackcapo EDC Junkie!!!!!

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    Murry Carter's 3 finger sticky method, phone book paper cuts, shaving and dropping a silk scarf from 14.35689" above the edge,if it splits into it is sharp enough...........

    BTW, I am totally joking about that scarf thing.:p
     
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  20. Tegan's Dad
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    Tegan's Dad Loaded Pockets

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    Just ordered a stropman HD compact with white and green compound. It's not that expensive for a nice hand-crafted tool so I figured I'd give it a shot. If I don't like it, I'll just give it to my brother who used to do my knife sharpening for me before I decided to learn myself.

    Thanks to everyone for the replies! It's very interesting to me to see what other people do, especially those with more experience than I have, and there's a ton of that on this forum.