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Thread: How to restore a straight edge on a cambered plane blade?

  1. #1

    How to restore a straight edge on a cambered plane blade?

    Bonjour fellow neanderthalians,

    I am trying to restore a straight edge on my smoother so blade after they got heavily cambered (0.25-0.5mm) on a deeply hollow brand new trend diamond stone.

    Since then, I have tried unsuccessfully to restore a straight edge on these smoothing blades. I am not ultimately shooting for dead straight but a very light camber, which is easy to add on the finest stone, given a straight edge to start from. It is really an infuriating feeling when you can only take a 2cm shaving from a beloved 4 1/2 smoother.

    I have a small tormek and a set of good diamond plates (300,600,1200). I usually grind at 25° on the wheel or coarse stone then sharpen and hone at 30° on the other plates, stones and strop, depending on the tool.

    I have tried to "start fresh" by placing the blade on my shooting board, and gently shooting it straight with by medium stone. It left me with a blunt edge, similar to a blunt chisel, slightly thicker in the middle. I then ground almost to the edge using the tormek, followed by the stones, with a LN guide, as balanced as possible.

    The tormek is not excellent at producing dead square edges by itself, it is all technique from the operator. The stones should be okay, but I have found it hard to fight the "belly" left by the previous camber, in the center of the blade.

    To this day, I have not managed to restore the edges to the straightness of my bevel up blades, being left with less than half the cambered I had before. Still kind of heavy.

    What would you recommend to correct this? Hone and sharpen the center only until it gets straighter?

    NB: I really can’t recommend trend diamond plates, the 300-1000 double sided ones. When I received the first one, I "primed" it using the back of my scrub and fore planes, to remove the eventual loose diamonds and get rid of the fresh aggressiveness. I did not notice at this time it was hollow on both sides as I used it for blades with heavy cambers (say 1 or 2mm). I ordered a new one but returned it as it was also hollow. I tested it at 0.2+mm, which translate to a 0.5mm camber when honing at 30deg.

    DMT stones I ordered since are much better it that regard.


    Regards from Cro-Magnon rock shelter o/

  2. #2
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    Derek Cohen has an invaluable website that covers many of these pitfalls. Bevel up blades are thicker and require grinding along the entire bevel to reset the cross section flat.

    (His linked article describes creating a camber, but the technique applies to returning to "square".)

    If you have a belt sander, it can make short work of this. Caution is in order, have the belt turning *away* from you so if the iron escapes, it isn't coming at you.

    Cool frequently in water to maintain temper.

    *****

    https://inthewoodshop.com/WoodworkTe...aneBlades.html

  3. #3
    Thanks Jim!

    Quote Originally Posted by Jim Matthews View Post
    Derek Cohen has an invaluable website that covers many of these pitfalls. ... (His linked article describes creating a camber, but the technique applies to returning to "square".)
    Derek publishes really nice content indeed, here or on his website.

    The article is however about creating camber on bevel up blades. My issue is more about straightening a cambered bevel down blade, which to my surprise proved much harder.

    This morning I managed to achieve a straighter edge by grinding a slight inverse camber on the tormek and then refining it very carefully on a 1200 grit diamond plate at a higher pitch.

    I have the feeling that new diamond plates require some usage to wear down enough so that the aggressiveness of the protruding diamonds averages, both in the center and the sides of the plate.

    I also have the feeling that using a honing guide, such as the eclipse or Lie Nielsen, tends to wear the center of the plate faster than the edges and thus, producing undesired camber. When sharpening freehand, it seems easier to use the whole surface more evenly.

  4. #4
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    Jerome — If I understand your question you are trying to get a 90 degree edge on your plane blade. I regularly test this angle with a small machinists’ square while grinding a new bevel. Try marking your blade edge with a black marker and check it frequently while you grind on your Tormek. Once you achieve a burr and are satisfied with the angle of your grind, you can go to your stones to remove the burr and refine your edge. You’re correct that new diamond stones are aggressive. This wears off after a few uses.

    While the Tormek would seem to be automatic, technique can be very important. Also, don’t forget to use your diamond TT-50 Truing Tool to bring your stone into proper condition. The stone can get uneven after lots of use.
    I wish that I knew what I know now... Rod Stewart from Ooh La La

  5. #5
    I have sharpened freehand for more than fifty years. You will have to judge whether the technique I use to reduce camber is something you can do.

    I start sharpening with the iron overhanging the side of the stone on the right side. The bevel is flat on the stone but almost half of the bevel is off to the right. I lean on the center of the iron as it rubs the edge of the stone.

    After a while I gradually move the iron to the left still sharpening as I go. This evens out the sharpening, which otherwise could be somewhat hollow in the center of the iron. Then I gradually move the iron so it overhangs on the left side and again put pressure so it works the middle of the iron. You still want the bevel in contact with the stone, not tilted over so it only rubs at the very corner.

    In an extreme case like yours, most of the sharpening is done with the overhang, just a little with the iron centered. I would aim for straightening out over multiple sharpenings.

    I finish up with the iron centered on the stone to smooth things out. This technique tends to even out the wear on the stone, which otherwise tends to wear hollow. In general I use this technique to lessen camber and keep the entire bevel on the stone to increase camber.
    Last edited by Warren Mickley; 07-24-2020 at 9:45 AM.

  6. #6
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    When I have to do this or address a very out-of-square blade, I joint the edge with some sandpaper on a flat surface with, holding the blade vertical and against a squared up block of wood until I've established a flat across the entire edge. Then I grind until the flat is almost gone- just a whisper of thickness left evenly across the whole blade, then hone on flat stone.

    This sounds similar to what you were doing with the shooting board, I think. Not sure why it didn't work. If you jointed a truly flat edge, and then grind until just a glint of that jointed flat remains, then the edge is going to be straight. Seems like you are adding a camber back in somehow.

  7. #7
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    I have not had trouble getting things square on my Tormek; assuming the sides are parallel to each other. It takes more work if they are not. If you live near Columbus, Ohio, stop by and we can sort it out.

    The real question becomes, how can you just flatten it out? It might help to draw a line that represents straight, especially if you are free handing things.

  8. #8
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    Quote Originally Posted by Jerome Andrieux View Post
    Bonjour fellow neanderthalians,

    I am trying to restore a straight edge on my smoother so blade after they got heavily cambered (0.25-0.5mm) on a deeply hollow brand new trend diamond stone.

    Since then, I have tried unsuccessfully to restore a straight edge on these smoothing blades. I am not ultimately shooting for dead straight but a very light camber, which is easy to add on the finest stone, given a straight edge to start from. It is really an infuriating feeling when you can only take a 2cm shaving from a beloved 4 1/2 smoother.

    ....

    Regards from Cro-Magnon rock shelter o/

    Jerome, the easiest way is to return the blade to straight, and then add the slight camber you want.

    The way I would do this is to push the blade (as it is) square into a grinder wheel or a disk sander. That will leave it straight across.

    Then I would hollow grind the bevel at the desired angle.

    Now you can add the fine camber with your coarse stone (that is when I do so). For me, this is a 1000 Pro Shapton.

    Finally, finish honing and polish the bevel.

    Regards from Perth

    Derek

  9. #9
    Warren - at what angle do you hold your blade in reference to your stone along its length?

  10. #10
    Quote Originally Posted by Derek Cohen View Post
    Jerome, the easiest way is to return the blade to straight, and then add the slight camber you want.
    thanks Derek, that is what I meant. It just appears difficult to get a perfect straight edge to start from. It seems that every time I hit the stones, a camber appears.

  11. #11
    Quote Originally Posted by Eric Rathhaus View Post
    Warren - at what angle do you hold your blade in reference to your stone along its length?
    My bevel angle is very near 30 degrees.

    I do skew the blade to the side when sharpening also. It is maybe 20 or 25 degrees from perpendicular to the long axis of the stone. This skewing is seen in many woodworking traditions because it is more stable and helps keep the angle constant. It sort of develops naturally.

    P.S. Let me know if this does not answer your question.
    Last edited by Warren Mickley; 07-24-2020 at 4:06 PM.

  12. #12
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    Quote Originally Posted by Jerome Andrieux View Post
    thanks Derek, that is what I meant. It just appears difficult to get a perfect straight edge to start from. It seems that every time I hit the stones, a camber appears.
    At this point one needs to determine if the cambering is caused by hollow stones or technique. If the stones have a lowered center, it will require side to side sharpening to make a straight bevel. Even this can fail if there is a tendency of the wrists to flex when moving side to side.

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

  13. #13
    Thanks Charles, I am not exactly aiming for a square edge but a straight edge. A perfect straight line one could say, not an arc or camber.

    I am quite seasoned when it comes to sharpening on stones and tormek, and my recent problems originated from a faulty stone, then using fresh new stones with a guide.

  14. #14
    Thanks Warren, I use a similar technique on water stones, but the edges of my new set feel unsafe to risk the blade edge over right now. I may have to wait until they wear a bit.

    I can’t remember how long I kept the previous set, maybe 7 or 8 years? I kinda regret them now.

  15. #15
    Quote Originally Posted by Robert Hazelwood View Post
    Seems like you are adding a camber back in somehow.
    ‘Thanks Robert,
    Exactly. A month ago, I replaced my worn out stones with a faulty trend one. Since then I bought a dmt set, and I guess they are not yet "broken in" and tend to be more aggressive on the edges.

    The technique you mention is indeed similar to mine, and I have used it many times for years, yet it seems that my current context has issues.

    I even inspected the blades themselves to rule out any flatness issues that could lead on an ellipse shape of the edge.

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