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Thread: Not another sharpening post :)

  1. #1

    Not another sharpening post :)

    A question for experienced free-handers. I notice almost invariably from the scratch patterns that I'm not hitting the corners of my blades and chisels as much as the center when I'm working on the backside. (I've check for flatness to .004 before starting and I found it still happens. ) I try adjusting my technique to add more pressure to these areas and eventually I even out the scratch pattern. Now I'm wondering if my adjustment just results in creating a slight camber that I don't want. Maybe I need to adjust my technique in a different way to get consistent amount of pattern? I raise this question because I sometimes end up applying so much extra pressure that I've started trying to work out other causes.

    Thanks for any pointers!

    Eric

  2. #2
    I think this must set a record for the longest time until the first reply to a post about sharpening.

    Are you sure your stones and the backs of your blades are flat? Flat to within .004" is not flat at all when it comes to sharpening -- that's about the thickness of a sheet of paper. I try to make sure that there's no visible light between a good straightedge and the back of a blade. If I can't see light, then my thinnest feeler gauge (.001") won't fit.

    When you're working the back of blades, it's important to make sure your stones are very flat. It's not because extreme flatness is necessary in and of itself, but because you want to make sure that as the blade moves from stone to stone, each stone consistently abrades the surface.

    Imagine that a 1000 grit stone is dished so that with a 1" wide chisel, the back of chisel will have a belly of .004". Then if you take that blade to the next stone (say, 4000 grit), and that stone truly is flat, you would have to either abrade an amount of steel equal to the thickness of a sheet of paper (which would be an enormous amount of work) or work the back of the blade in separate sections (which is what it sounds like you're doing).

    What kind of stones are you using, and what are you doing to keep them flat?

  3. #3
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    I echo Winston's remarks, and add a query as to whether you are rocking the blade as you lap the back?

    Regards from Perth

    Derek

  4. #4
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    I notice almost invariably from the scratch patterns that I'm not hitting the corners of my blades and chisels as much as the center when I'm working on the backside.
    My question would be if you are going side to side?

    For me an in & our motion works. It also helps to apply even pressure. One of my small circle guides/templates works well for this:

    Small Circle Guide.jpg

    It can work on stones or abrasive sheets:

    Working Blade Back Circle Template Press.jpg

    There are other ways to apply pressure. My circle templates just happen to be close at hand.

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  5. #5
    Hi Winston - I use microfilm and granite inspection block so that I'm not concerned that the surface I'm using to sharpen, hone, and polish is flat. I'll go back and use my 0015 feeler gauge to see if the backs are convex.

    Quote Originally Posted by Winston Chang View Post
    I think this must set a record for the longest time until the first reply to a post about sharpening.

    Are you sure your stones and the backs of your blades are flat? Flat to within .004" is not flat at all when it comes to sharpening -- that's about the thickness of a sheet of paper. I try to make sure that there's no visible light between a good straightedge and the back of a blade. If I can't see light, then my thinnest feeler gauge (.001") won't fit.

    When you're working the back of blades, it's important to make sure your stones are very flat. It's not because extreme flatness is necessary in and of itself, but because you want to make sure that as the blade moves from stone to stone, each stone consistently abrades the surface.

    Imagine that a 1000 grit stone is dished so that with a 1" wide chisel, the back of chisel will have a belly of .004". Then if you take that blade to the next stone (say, 4000 grit), and that stone truly is flat, you would have to either abrade an amount of steel equal to the thickness of a sheet of paper (which would be an enormous amount of work) or work the back of the blade in separate sections (which is what it sounds like you're doing).

    What kind of stones are you using, and what are you doing to keep them flat?

  6. #6
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    Grip? One finger in the center of the iron? maybe go with 2 fingers held more towards the edges, than in the exact center.

    As for that "Feeler Gauge"? I gave mine all away, so a mechanic friend of mine can set Ignition Points on vintage cars....and that is about all the use I have ever found for them, anyway....

    And, yes...I do freehand sharpen all the time....

  7. #7
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    I believe the inestimable David Charlesworth recommended the method I use.

    Flatten the stone, for starters.

    Pass the blade across the narrow part of the stone, so that the blade comes all the way off the far edge.

    Move along the length of the stone (I work left to right) and check the polish for even distribution.

    ****

    I find that if the results on a given stone are unsat, it is faster to go one coarser grit and verify all of the back is "polished".

  8. #8
    Thanks, Steven. So to sum up your advice, it isn't machine work so flatness of the back of the iron past .004 isn't where the problem lies. Work on my technique more.


    Quote Originally Posted by steven c newman View Post
    Grip? One finger in the center of the iron? maybe go with 2 fingers held more towards the edges, than in the exact center.

    As for that "Feeler Gauge"? I gave mine all away, so a mechanic friend of mine can set Ignition Points on vintage cars....and that is about all the use I have ever found for them, anyway....

    And, yes...I do freehand sharpen all the time....

  9. #9
    Thanks, Jim. My stones are as flat as needed by a machinist. I alternate directions as I move up in grit so that I can see if I'm removing the scratch pattern from the coarser stone, moving the iron along the length so that the scratch pattern is perpendicular to the side of the iron then moving the iron parallel to the narrow side of the stone so that the scratch pattern is parallel to the sides.
    Quote Originally Posted by Jim Matthews View Post
    I believe the inestimable David Charlesworth recommended the method I use.

    Flatten the stone, for starters.

    Pass the blade across the narrow part of the stone, so that the blade comes all the way off the far edge.

    Move along the length of the stone (I work left to right) and check the polish for even distribution.

    ****

    I find that if the results on a given stone are unsat, it is faster to go one coarser grit and verify all of the back is "polished".

  10. #10
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    A picture might be illuminating.

    My doubt is that you are pursuing flatness appropriate to machine tooling, which may not be necessary for getting sufficient flatness in wood joints.

  11. #11
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    Quote Originally Posted by Derek Cohen View Post
    I echo Winston's remarks, and add a query as to whether you are rocking the blade as you lap the back?
    I have had that problem in the past, be diligent. It is easy to rock the blade while going back and forth.

  12. #12
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    Quote Originally Posted by Andrew Pitonyak View Post
    I have had that problem in the past, be diligent. It is easy to rock the blade while going back and forth.
    Eric, if you start with a surface that is even minutely curved, running the blade back-and-forth, and trying to keep it flat, will just preserve the curve. It will not get flat .. unless pressure is placed on the high spot. If you (unwittingly) rock the blade, it will increase the curve. The sides will show this. A quick way to avoid this situation is to use David Charlesworth's Ruler Trick - that is why this method works well.

    Regards from Perth

    Derek

  13. #13
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    I always have relied on HOW the chipbreaker mates to the back of the iron.....I am looking for a gap-free meet up......and best way to check is simply hold the two parts together, and look between them into a strong light source....Don't see any light coming through? Good to go, go to work.

    Need to work on applying a consistant pressure across the entire edge of the iron.....one finger pressing down in the middle of the iron leads to just the middle getting sharper the the edges,,,or, a finger pressing down on just the outside edges...means you'll wind up with a slight camber....depending on how much pressure is used....from just a slight bit off at the corners, to a full, radiused cambered edge ( scrub plane size).

    Sometimes, it is easier to use both hands, just keep the pressure equal .

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