Testing sharpness, and what about serrated?

Discussion in 'Sharpening Station' started by Drayquan, Mar 21, 2019.

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  1. Mar 21, 2019 #1

    Drayquan

    Drayquan

    Drayquan

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    After sharpening a regular edge there are many easy and fairly accurate ways to test its sharpness level: paper, sponges, hair, or actual food like thinly slicing tomatoes, etc.

    Different levels of paper thickness tell you a lot: thicker stock like white printer paper usually being easier to cut vs newspaper or phonebook paper for example.

    Newspaper *in my area* happens to have a significant “grain” direction; its far easier to slice vertically with a 300-600 grit finish, whereas a sideways slice requires a more refined 800-1000+ grit edge to cut cleanly.

    Straight push cutting requires further refinement, same with slicing a tomato across without holding it in place, shaving arm hair with various levels of ease/smoothness, cutting free-dangling hair etc. All of these variables clearly show the sharpener a wide range/spectrum of sharpness level achieved.

    I need something like this with serrated knives.
    Aside from food (like fresh Italian bread with tough crust and soft interior, etc), what type of common items are a good method of testing a serrated edge?
    I’ve been using thicker paper, sometimes folded once or multiple times, cardboard, etc, but it seems really hard to tell for me, I really can’t judge a serrated edge well at all wth these methods. Any recommendations (aside from buying a bunch of test food)?
     
    Last edited: Mar 21, 2019
  2. Mar 21, 2019 #2

    Drayquan

    Drayquan

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    I should mention, I’m very new to sharpening serrated.
    I’m using a belt grinder with various grit levels (1-inch wide belts), using the edges of them to get into the grooves. The grinder has various adjustments to allow a little more belt flexibility for this. I’ll also use a medium DMT rat-tail file, and/or high quality wet/dry sandpaper wrapped over the spine of a large knife or honing rod.
     
    Last edited: Mar 21, 2019
  3. Mar 21, 2019 #3

    Foltest

    Foltest

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    I dont test serrated edges at all, I use only rough stone, burr is created, deburred, thats it. I dont see any added benefit from further refinement, you arent going to do smooth cutting with serrated edge anyway
     
  4. Mar 21, 2019 #4

    chinacats

    chinacats

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    Cut test for both preceded by 3 finger test on regular edge.
     
  5. Mar 22, 2019 #5

    SilverSwarfer

    SilverSwarfer

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    Interesting there’s no mention of a fingernail test above; it’s been a metric for me for years.

    Lately with experimentation of more polished edges, I have found some limitations in this test. That is to say an ultra sharp, highly polished edge will “bite” into the nail less with higher polish and refinement- thus reducing effectiveness in indicating sharpness of “toothless” edges.
     
  6. Mar 22, 2019 #6

    Michi

    Michi

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    Why would I want to test with anything other than what the knife is meant to be cutting? Maybe test a bread knife with bread maybe? And test a tomato knife with tomato?

    Why would I even care how well a bread knife cuts cardboard or paper?

    If you are are worried about cutting food for testing, just have a snack while you are sharpening. By the time the bread is all gone, the knife is probably sharp, too :)
     
  7. Mar 22, 2019 #7

    inferno

    inferno

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    I only do one real test. i take the edge to my thumb and feel it. NOT along the length of edge BUT ACROSS. you can feel it right away if its sharp or dull. you feel if it has bite or not.
    then the grit you used will tell you how sharp it was.

    I have seen other known smiths suggesting moving your thumb along the edge forth and back and see how it sticks kinda. not for me imo!! since i would slice my thumb in half then. you would have to be very very delicate doing this. or have very much experience with it.

    I can do my method while/during sharpening customers knives. I'm fairly certain this will only work with fairly wet thumbs though, your skin needs to have absorbed some water. i only do it while sharpening so my hands have been wet for several minutes. it feels totally different when dry. i have no feel for this then. then i try to wet my thumbs quickly to get any mileage out of this method.

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

    to impress people i can slice a paper, and if its low/no noise doing it then its sharp. and if i can do 180 degree turns in the paper then its as it should.
    this is mostly to impress people that dont know jack sh1t about this though. I only use the sound level for myself, that will tell me how good i did a job, and also my thumb. i dont regard push/pull cutting as any proof of sharpness since i can sharpen my iwasaki razor on a 16k then cr-ox then leather and it will still not push cut paper very well, but it will shave like a fukcing lazersword. so its mostly a parlor trick imo.

    just test it your body imo. it gives a fairly good representation, the actual level will be determined by the actual stone you used. I can shave hair of a 220 stone. does that mean its sharp or even good?? no!

    i'd say it works just the same with serrated knives. some serrated ones are different though compared to tothers but these general rules will apply to all of them imo.
     
  8. Mar 23, 2019 #8

    HRC_64

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    A properly sharp serrated bread knife will slice the fook out of paper
     
    Last edited: Mar 23, 2019
  9. Mar 23, 2019 #9

    K813zra

    K813zra

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    I used to do all kinds of stuff like shaving hair, push cutting news print and or paper towels etc. I still will if I am testing out a new stone just to ease my curiosity. But honestly the vanity of that stuff has worn off.

    But in use, in my kitchen, I normally sharpen before a meal prep so I can test on product. Prior to that I will inspect the edge under light and do the three finger test. If it is a super quick touch up I might just kiss the edge to the stone a few times without testing at all. :p
     
  10. Mar 23, 2019 #10

    inferno

    inferno

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    I can actually just look at an edge and determine if its (quite) sharp.
     
  11. Mar 31, 2019 #11

    Drayquan

    Drayquan

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    Yep, this is possibly the easiest when held under a light to highlight any surface area along the edge. I dont have great eyesight like I used to, but I'm thinking of getting a good quality magnifying glass for this type of thing. Good smartphone cameras can be helpful for this with high zoom.

    I do this of course, while my groceries last ;)

    With the volume of blades that come through my workshop, if I were to test everything on actual food, I'd either be living IN a gigantic compost pile, or living AS a gigantic, human compost pile.

    Newspaper from the previous day that was headed to recycling is free and DOES give accurate sharpness testing *if used properly*.

    The low/no sound is key, as Inferno said. I agree, its easy to slice-cut a straight line through paper to impress newbies, even with a 220 finish, but you'll HEAR that rough sound. Being able to cleanly cut tight curved/wavy turns with relative silence when listening very closely is a great indicator that it's at a decent standard. Food is ideal though, I do agree :)

    To test everything on my fingers, well I do, then after the 20th blade of the day, the feeling starts to become difficult to tell lol

    So, instead, my workshop looks like I have an office shredder running 24/7 covering up some incriminating fraud paper-trail a mile long ;)
     
    Last edited: Mar 31, 2019

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