Manual Knife Flattening & Thinning?

Discussion in 'Maintenance, Tinkering & Embellishment' started by Eli Chaps, May 27, 2020.

  1. Eli Chaps

    Eli Chaps Basic Member Basic Member

    Apr 20, 2018
    So I want to get deeper into flattening and, as needed, thinning the primary grinds of my knives.

    I did some experimenting on Dexter Russell vegetable cleaver with so-so results. I don't have water stones so on that one I first ran it over a Fine India stone. Yes, it scratched it all up. But I used 600 grit sandpaper wrapped around a 2"x8" Arkansas stone to help smooth things out. But, it was of course still pretty scratched.

    For that dabble the functioning part was good, it just looked pretty haggard.

    I decided I wanted to work on my budget friendly and several years old Wusthof Gourmet 8" Chef's knife. This time I start with the 600 grit paper. Obviously this greatly reduced the deep scratches but certainly left the finished scratchy and uneven. It's pretty remarkable how inconsistent the blade grind is when you do this so my thought was to start with the 600 so it would be aggressive enough to remove material but maybe not be as harsh as the India.

    I want to spread this out over time and will need a few more sessions to get the blade just even let alone do any real thinning. While I'm not overly concerned about aesthetics, I'd also like the finished product to look semi-decent. A matte finish would be fine by me. I'm thinking that after getting it flat maybe bump to 1k+...?

    I would also like to start exploring this on a Manix 2 and Dragonfly 2.

    Thoughts? Wondering about the use of the paper wet or with oil? Different approaches?
     
  2. jpm2

    jpm2

    Nov 19, 2014
    I've done this to a good many knives and so far never found any production models that were perfectly flat... flat stones/plates don't lie.

    I start out with sandpaper on a known flat surface, or diamond plate just to see what I'm dealing with. If it's close to being flat (rare), and not a great deal of metal needs to be removed, I'll use ~180 grit till I'm close to the thinness I want, then refine from there.
    If it's not close to flat (most), or a lot of metal needs to be removed, even if it is flat, I'll take it to a 100 grit sic stone to get it close, then ~180 on known flat or diamond plate, and so on.

    Speaking of flat surfaces for sandpaper, I recently acquired this, and really like it.

    [​IMG]

    Depending on blade steel and how much needs to be removed, it can take a lot of sandpaper. This is why I value a coarse sic stone so much.

    The coarse sand paper I wear out can be used in the finishing stages.

    Abrasives I've used are most all grades, grits, and type of sandpaper, silicon carbide stones, aluminum oxide stones, & diamond plates. All paper used dry.
    Nothing powered for me, I'm in no hurry, and take my time.

    I'm always surprised how many premium blades are so far from flat.
     
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  3. Eli Chaps

    Eli Chaps Basic Member Basic Member

    Apr 20, 2018
    Thank you. I have course stones for sure but figured I'd be plowing in some deep scratches so avoided that. But I reckon it comes down to the refinement.

    What progression up do you use? When do you call it good in terms of finish?
     
  4. Ourorboros

    Ourorboros

    421
    Jan 23, 2017
    I don't have a ton of experience with this, but from what I gather - this is where having a big run of waterstones really shines. If you don't want those deep scratches, you'll be working your way up. A 6K waterstone - roughly the equivalent of a black arkansas stone with some wear in - will leave you somewhat under a mirror finish. You won't get mirror until you use something 1.5 microns or smaller.
    Some of it is the time you spend on each stone, so if you jump from 1K to 6K you'll be spending time getting those 1K scratches out. Smaller jumps makes the day easier.
     
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  5. jpm2

    jpm2

    Nov 19, 2014
    On rare occasions, I've taken it to 1 micron diamond paste, which is mirror to the eye.
    After the coarse stone, 180 grit aluminum oxide paper, then 400 grit silicon carbide paper till it's completely worn. This gives an almost mirror finish going into the paste.
    Most of the time I stop at worn 180 grit alox.

    If you have some 180 aluminum oxide paper, try it after your coarsest stone till it's worn smooth and see what happens.
    Do the same with 400 or higher silicon carbide paper.
     
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  6. HeavyHanded

    HeavyHanded

    Jun 4, 2010
    I've done a bunch by hand before vowing never to do so again.

    Normally make a grid with Sharpie across the entire face and take it to my most coarse stone. Repeat repeatedly. This is where I lean all over it. It can take a lot of sessions if you're planning on removing a lot of steel. Yes, virtually every single knife you do this to will show significant surface imperfection and it can take a lot of work just to remove that, let alone reshape the entire blade face.

    It is well worth it in terms of performance. I started out by converting a number of sabre grinds to convex (a relatively easy process compared to doing a FFG conversion). Then just work up on hard stones till you get close to the desired thickness. Switch to wet/dry over a slightly conformable surface such as piece of hard leather or soft wood to get the cosmetics down. A slurry can do a good job to finish when it comes to hiding imperfections.
     
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  7. Eli Chaps

    Eli Chaps Basic Member Basic Member

    Apr 20, 2018
    Thanks for the inputs all.

    Yeah, my thought was get the surface imperfections out and then here and there do some passes to slowly start working the overall profile thinner. But now I might just go for it.
     
  8. Mr.Wizard

    Mr.Wizard

    Feb 28, 2015
    P600 is way too fine for thinning in my opinion. It's actually a good finishing grit and it will look nice if you lay down the scratches carefully with fresh paper. This is called a hand rubbed satin finish.

    For thinning I have used as coarse as 50 grit paper. As you discovered blade grinds are rarely even so you will need to remove a lot of metal. See photos eveled provided:

     
    Last edited: May 28, 2020
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  9. Eli Chaps

    Eli Chaps Basic Member Basic Member

    Apr 20, 2018
    Yep. I'll stop being a scaredy cat and grab some 180 I have. :)
     
  10. Ben Dover

    Ben Dover Gold Member Gold Member

    Aug 2, 2006
    Finish on wet/dry 2000- 2500 paper used WET!
     
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  11. Ourorboros

    Ourorboros

    421
    Jan 23, 2017
    FWIW most people stop at not ugly/hazy mirror.
     
  12. Eli Chaps

    Eli Chaps Basic Member Basic Member

    Apr 20, 2018
    Yeah that's my target. This is a foray into function over form.
     
  13. Mr.Wizard

    Mr.Wizard

    Feb 28, 2015
    When you want to add the form to match the function here is how to do a hand rubbed satin finish.



     
  14. Eli Chaps

    Eli Chaps Basic Member Basic Member

    Apr 20, 2018
    I rooted around in my sandpaper and found I have ample 100 and 220 grit. So, I started with the 100. I have to say, it was a little nerve racking to just slap my knife down on course paper and go at it. But I did. Then I switched to 220 for a good while and lastly 600.

    Now this is fun but not sure I want to make a habit of it. I can understand why @HeavyHanded says he's sworn off it. To get really serious about thinning, this would take a good bit of effort. You could stretch that over different sessions but any real material removal certainly will take time. But for a knife here or there to smooth it out and maybe focus on specific areas it is pretty interesting and I think worthwhile.

    My goal to start was:

    1. Get confidence.
    2. Smooth out the factory grind imperfections.
    3. Thin the edge shoulder a bit.
    4. Smooth the spine edges near the handle.

    I've largely accomplished all of those things. For me, this knife is an absolute workhorse so again aesthetics were way down on the list.

    I only had about 2/3 of a sheet of 600 paper left so I need to grab some more and spend some more time on finishing, really just for visuals. But I also stopped because now that I feel better about doing this, I think I will give this another session at some point back at the 100 grit and work back up. You can still see a hint of the factory marking on the blade so I didn't remove too much material overall but again, I did do alright at the shoulder. And the sharp edges of the spine are much better now.

    I know, I know, still marred up but it's actually really smooth. The bright sun sure does show the scratch lines. Like I said, I'll get back at it. The handle sort of means it will never be perfect visually.

    [​IMG]

    [​IMG]
     
  15. jpm2

    jpm2

    Nov 19, 2014
    Don't be afraid of going back to the 100 grit... use the crap out of the same 220, it'll eventually leave shallower scratches and a finer finish than new 600.
     
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  16. Eli Chaps

    Eli Chaps Basic Member Basic Member

    Apr 20, 2018
    I agree and thank you.
     
  17. David Martin

    David Martin Gold Member Gold Member

    Apr 7, 2008
    I have done some by hand on a stone and I agree w/ Heavyhands. It is time consuming. I did some on a coarse then fine India and the scratches weren't too bad. I then took it to a sisal buff wheel and black rouge. At this level it came out great. The sisal wheel really blends in the scratches to a soft satin finish. It doesn't take a lot of metal removal. Less than a 16th" from each side. It was 440C steel. Good luck, DM
     
    Last edited: Jun 2, 2020
  18. 115Italian

    115Italian

    Nov 13, 2015
    I ran my tops msk on a dmt fine grit diamond plate. Its a scandi grind but with a micro bevel. I wanted it to be a true zero grind. So I went at it. 1095 steel and it took a while. Got it flat on both side right down to an apex. Its a lot of work but was worth it. I finished it off with 600 grit wet sandpaper.
     
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  19. Eli Chaps

    Eli Chaps Basic Member Basic Member

    Apr 20, 2018
    Another update...

    And again, trying to be as transparent as possible for all who come along...

    I apologize for these pics as it is a dreary rainy day and I can't get some good natural light shots. What you see is largely shadows and light play. The blade on both sides is actually pretty even.

    [​IMG]

    [​IMG]

    Geometrically speaking, I think I'm in a happy place. The blade is flat, I removed a smidge of overall thickness, and more importantly, thinned the edge shoulder.

    It slices like a dream. It honestly made a very noticeable difference in cutting performance and I couldn't be happier. Those are sliced paper towels around it. I've been using it on veggies the past few days and it really shines now.

    Aesthetically speaking, obviously it still needs work. I think maybe going tip to heel might be better than spine to edge for that. I'll play around with it but not sure I have the patience to make it truly satin again.

    I've learned a lot that I'd be glad to share if anyone is interested but the main question I guess is, would I do it again?

    Yes and no. I love the performance but if it is a knife I care about perfect surface finish, then I'd have someone do it with power gear. I don't have many of those kinds of knives so I'm good. :)
     
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  20. David Martin

    David Martin Gold Member Gold Member

    Apr 7, 2008
    Yes, thinning it, even a little will make a noticeable improvement in slicing performance. Good effort. DM
     
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