(partly) adding curve to flat spot

Discussion in 'Sharpening Station' started by childermass, May 15, 2019.

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  1. May 15, 2019 #1

    childermass

    childermass

    childermass

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    Hi all!
    I have a question:
    I got a knife with a huge flat spot in front of the heel (over 10cm). I would like to add a gentle curve to the first few centimeters closer to the tip to make board contact a little more smooth when rocking.
    Any tips on how to approach this? If possible I don’t want to do this in one session but rather add the curve during continuous sharpening.
     
  2. May 15, 2019 #2

    HRC_64

    HRC_64

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    IMHO... only way to get proper profile trasitions = breadknife it
    just use light pressure, you don't need to crush the edge or anything crazy...
     
  3. May 15, 2019 #3

    childermass

    childermass

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    Where did the rest of your post go?
    I was afraid that breadknifing will be the answer.
    You mentioned a backbevel in your full post, can you please explain to me what that means?
    Thanks!
     
  4. May 15, 2019 #4

    HRC_64

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    This is why I tried to keep my response brief. it may be better to let other people chime in. ;)

    Once you decide how make the profile alteration, there is perhaps further discussion about how to make
    a profile alteration more generally...ie...attack the front or the back
    (or a combination includin the back)...and what are the pro and cons of each

    A backbevel is done at the back of the flat spot to avoid the profile ending in a "thud",
    it can be done very subtle to keep most of the inherent "flatness" in terms of cutting,
    but its noticeble addition to 'fluidity'.

    I wouldn't get into this dicussion too far tho until you are comfortable with breadknifing,
    otherwise you'd need to be a jedi-master sharpener to make these kinds of alterations.

    Don't let this intimidate you, however, as very subtle changes can do a lot of good
    and re-establishing the edge after a very sutble change is not that bad.

    But the key is SUBTLE ... using light pressure...this is not "reprofiling" like
    turning a tipped knife into a santoku or something...its more blending
    in a smooth profile from one with a couple flaws or whatever...
     
    Last edited: May 16, 2019
  5. May 16, 2019 #5

    chinacats

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    Just make your cutting motion on the (side of a) stone...you'l wind up with a rather natural profile that cuts well (after thinning).
     
  6. May 16, 2019 #6

    Benuser

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    Try first by just lifting the heel a tad.
     
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  7. May 16, 2019 #7

    childermass

    childermass

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    Thanks everyone, some great advice here already.
    I will try to lift the heel a bit before I go deeper into the profile and see how that works. This will be necessary anyway, I realized that the last centimeter of the blade is a little higher than the flat area in front of it.
     
  8. May 16, 2019 #8

    Smashmasta

    Smashmasta

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    Ideally breadknife on a diamond stone because bread knifing is also the most efficient way to gouge whetstones, especially low grit since they're so porous.
     
  9. May 16, 2019 #9

    galvaude

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    1) breadknife to desired profile. Coarse crystolon on is about the best for this

    2) thin

    3) refinish to whatever you like

    4) set new edge
     
  10. May 16, 2019 #10

    chinacats

    chinacats

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    If you're referring to the heel itself, it should be just a touch higher or your knife will thud when you cut...it would be most annoying.
     
  11. May 16, 2019 #11

    HRC_64

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    also, its easier to breadknife a slightly dulled knife ...
     
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  12. May 16, 2019 #12

    labor of love

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    I hate “heel clunk” with a passion, hope everything works out for you.
     
  13. May 16, 2019 #13

    Benuser

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    That lifting of the heel is quite subtle. Just measured and the heel is perhaps a millimetre higher than the lowest point, which is at a distance of some 5mm from there.
     
  14. May 17, 2019 #14

    childermass

    childermass

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    That sounds quite doable. I got an old hardly used Carborundum combo stone lying around so I will possibly start with that.
    Going to lift the heel a bit in the process too.
    Pretty curious how this works out, I will keep you guys updated.
     
  15. May 27, 2019 #15

    childermass

    childermass

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    Gave it a go this weekend, so here is a short update:
    Before I started, I checked the profile on a flat piece of Granite. There I realized that there was a slight overgrind in the flat portion of the blade and a spot around one centimeter in front of the heel that stuck out a bit.
    I used my Carborundum stone for breadknifing which worked really well, just a few light cutting motions on the stone did the trick.
    The flat portion is still pretty flat, I didn’t want to take off too much material just to make it curvy, but I managed to even out the profile and get rid of the overgrind and the part that stuck out.
    The knife performs way better now, the rocking motion is more fluid and I only get some minor clunk when I’m using too much force and all of the flat hits the board too fast.
    Sharpness is not quite there yet, I think I was a little too easy on the thinning and my sharpening angle was a bit too high, but this will be an easy fix. Also the knife is not as beautiful as it was anymore, after thinning you see all the low spots in that blade road.
    Thanks everyone for your comments and tips!

    Unfortunately I forgot to take pictures of the knife before I started, so there will be no before after shot.
     
  16. Jun 2, 2019 #16

    Benuser

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    Probably unnecessary: do the thinning along the long side of your stone.
     
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  17. Jun 2, 2019 #17

    psfred

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    I think you found the worst issues just getting the edge straight.

    If you want to gradually grind a curve, just work that part of the edge twice when sharpening. That will gradually remove steel at that point without the bother of grinding off the edge and restoring it.

    You will have to thin that area more often than the rest of the knife.
     
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  18. Jun 3, 2019 #18

    Benuser

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    Exactly. What takes us to the likely origin of the problem: a lot of Japanese knives have a thickening at the heel, starting at some 3/8". (By the way, that's what makes the value of choil pics somewhat relative). If one doesn't give special attention to that area by sharpening longer and verifying with a marker, the heel will start to protrude.
     
  19. Jun 3, 2019 #19

    childermass

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    Took the knife to the stones again last week. I did a little more thinning and reground the edge at a lower angle. I managed to even out the blade road some more making the knife look prettier and got it to a very satisfying level of sharpness.
    The heel will definitely take more attention in future sharpening sessions as will the area in front of the initial overground section. After thinning it became quite obvious that the overgrind extends over the whole height of the blade road on one side of the blade as the stones barely touched that area at all. Also burr formation was a lot quicker there than on the rest of the knife.
    It’s not that bad though, now that I know of this issue, I can properly address it in future sharpening sessions until it goes away.
     

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