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Thread: The mirror edge - is it necessary?

  1. #1

    The mirror edge - is it necessary?

    I've believed that the best cutting edge is achieved when we sharpen plane blades to a mirror polish.

    I understand that this level of honing is important on card scrapers and smooth planes where you are trying to leave a surface that is ready for finishing.

    However, for roughing work - like on a jointer or jack plane blade, is it really necessary (especially when you plan to follow up with a polished smoother?)

    I sharpen my lathe tools to a scratchy 80 gt, and they cut just fine. I was sharpening a jack this morning and started with 150g, got distracted, and forgot to hone before I reinserted the blade into the body. It cut fine.

    In fact, might edge retention be better on a coarser honed blades?

  2. #2
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    I doubt edge retention would be better, with very coarse visible scratches it seems like every scratch would be kind of like a tiny fault line, kind of like scoring drywall or even steel before you snap it. As far as the mirror polish goes, yes a foggy surface is indicative of microscopic scratches but really does it matter if the wood surface has grooves on it that are a micron in width? I doubt it. I think the mirror polish is way overrated.

  3. #3
    I think Ron Hock addressed this question in his "perfect edge" book, but I'm not certain.

    From my experience, absolutely not. What does your experience tell you, other than this one event? Perhaps you got a lucky impedance match this time. How is that jack working on hard maple? When I'm on my game, I can easily feel the difference in effort required by a dull vs. a sharp blade. So there's one data point. And what are you left with after a coarse blade gets dull? I'd guess, a rehab session at the grinder. So, there's another reason to go finer. It removes far less steel per touch up. And perhaps this isn't a direct response to your question, but I want an orderly and extremely refined edge as a "baseline". As work progresses, I can look at a leading edge and tell how far it has degraded

    I've pulled scores of planes and chisels out of drawers over the years from carpenters, family members, friends. Every single one was either unusable or barely on the cusp of functionality. Many of them were only a fraction of their original length. These guys actually used the tools to make a living or to accomplish important tasks and they found what worked for them: A very temporary serrated edge that was quick and easy to redress.

    I think this is like the oil "discussions" on motorcycle forums. They always turn into internet food fights.
    Last edited by Russell Sansom; 08-14-2011 at 2:47 PM. Reason: spelling

  4. #4
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    A dull blade will still cut, just not as efficiently as a sharp blade.

    In my experience it is easier to maintain a blade at close to sharp than it is to take the time to restore the edge after it gets to the point of too dull to do its work.

    Of course with scrubs, jacks and jointers we are not talking about taking sub thou shavings. But I can usually tell how sharp my blade is by how thin of a shaving it can take. Even if the work at hand is hogging off a 0.010 shavings, it seems to work better if the blade is as sharp as is possible.

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

  5. #5
    Quote Originally Posted by Jim Koepke View Post
    A dull blade will still cut, just not as efficiently as a sharp blade.
    But at what line do you make the point of efficiency ?
    Couple swipes on a course/ medium stone and back to work

    or

    testore the edge to mirror quality?


    This is from my carpentry experience where you could quickly sharpen the chisel on the belt sander and get back to work after dulling or chipping the edge on site
    Carpe Lignum

  6. #6
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    Sometimes if we look outside the box (planes and chisels) we can find the logical answer. I do not think those barbers of yesteryear had it wrong nor do I think that wood carvers have it wrong today when they strop the edge to a mirror finish. A good Shapton stone of 16K or even 30K leaves an edge every bit as polished as the barbers or carvers leather strop.

    Ed

  7. #7
    I keep a sheet of Wet-Dry sandpaper 600 grit on my sharpening base (granite from a sink cutout).

    When a blade is reluctant, I touch up with that. When that's not enough, I sharpen again.

    600 grit does NOT produce a mirror edge, but it is sufficiently sharp to work.

  8. #8
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    Quote Originally Posted by phil harold View Post
    But at what line do you make the point of efficiency ?
    Couple swipes on a course/ medium stone and back to work

    or

    testore the edge to mirror quality?


    This is from my carpentry experience where you could quickly sharpen the chisel on the belt sander and get back to work after dulling or chipping the edge on site
    Most of the time my standard is to not let blades get past needing a few passes on an 8000 water stone. For chisels I do keep a strop handy and touch them up regularly as I go.

    For my smoothing planes and block planes my goal is to not have to do more than a few quick swipes on a hard Ark stone or maybe a 4000 then 8000 water stone followed by stropping.

    Sometimes though the blades do get to where they have gone too long for my preference and they need a few swipes on a 1000 grit water stone.

    jtk
    Last edited by Jim Koepke; 08-14-2011 at 4:54 PM.
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  9. #9
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    Jim...

    This reminds me of an old and to this day very true saying of my mothers (God rest her soul) on fuel levels in cars..

    "Once you fill the tank, it doesn't cost you any more to operate your car on the top-half of the tank than it does to run on the bottom half"...
    One can never have too many planes and chisels... or so I'm learning!!

  10. #10
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    I've never made a mirror polish a goal yet all my chisels have it. I just sharpen up (1,000/4,000/8,000) and there it is. If your edges are working without, don't worry about it.

  11. #11
    Nope, but it sure is pretty!!! With my new water stones, that pretty equals "really sharp."

  12. #12
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    I use a mirror edge. When carving on woods that are good and hard,the polished edge leaves a polished cut. When doing very small,detailed carvings,like the Lion's head violin neck,I want every cut to be cleanly cut and polished. I haven't posted pictures of my boxwood lute rose(can be seen at George Wilson Guitar Maker),but that,and some of my other carvings are just too small to be sanded,or cleaned up. The surfaces were left as cut.

  13. #13
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    I polish my edges to mirror sharp, though I recognize that "mirror", while necessary for the absolute sharpness, is not sufficient - the bevel geometry also has to be correct. But the reason I do it to all of my blades has little to do with the finish left on the wood - it has to do with the effort required to push a plane across a wooden surface. At least in my hands, there's a good deal of difference between moderately dull and razor sharp.

    But - it doesn't take me any more time to produce a mirror polish than it does a coarser edge, because my blades go straight from the grinder onto an 8000 grit polish stone. Roughly speaking, 4 to 6 strokes is sufficient to produce a mirror on the cutting edge, and I've never seen the need to "save time" by only using 2 or 3 strokes.

  14. #14
    Quote Originally Posted by Jim Koepke View Post
    Most of the time my standard is to not let blades get past needing a few passes on an 8000 water stone. For chisels I do keep a strop handy and touch them up regularly as I go.

    For my smoothing planes and block planes my goal is to not have to do more than a few quick swipes on a hard Ark stone or maybe a 4000 then 8000 water stone followed by stropping.

    Sometimes though the blades do get to where they have gone too long for my preference and they need a few swipes on a 1000 grit water stone.

    jtk
    I try to keep mine polished to but on job sites I find hidden nails and painted wood just seems to dull a plane faster than anything
    so out comes the belt sander when I get home I try and bring back the to the original.
    A sharp chisel is nice when mortising hinges and hardware but few people will see the finish of the wood under the butt
    Carpe Lignum

  15. #15
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    I don't necessarily aim for 'polished' as I do for 'sharp'. Often, the polish is a by product of the extreme sharpness I prefer in any blade I have.

    I'm quite sure I'm more OCD over sharp than 90% of folks here, maybe more than that even.

    The reason for the OCD is simple, there's another by product of making a woodworking blade stupid sharp.

    A genuinely SHARP blade is incredibly forgiving. Half the problems you read about here and elsewhere about edges failing, tear out, planes not being able to smooth xyz wood. Most of them can be solved with a very, VERY sharp blade.

    Some folks ask, wonder and are bewildered at why some folks strive to get their blades so sharp. Take note of them, and then see how often the same people ask questions about why they can't manage something, and how it could be attributed to lack of sharpness.

    No, it doesn't matter how you get the things sharp, just that they are sharp.

    Stu.

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