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Thread: Hollow Grind

  1. #1
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    Hollow Grind

    Been meaning to ask the question, "if you hollow grind, why do you do it"? I do it because I use a Tormek and since it uses a wheel. . . Some will argue that because the edge is thinner the blade will dull easier. I'm not so sure. I believe it is dependent upon the hardness/temper of the blade. What say you?
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  2. #2
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    Re: Hollow Grind

    I'm no expert, but I'm inclined to say that given equal hardness/temper the hollow grind will wear faster.
    art

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  3. #3
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    Re: Hollow Grind

    Quote Originally Posted by Johnboy View Post
    Some will argue that because the edge is thinner the blade will dull easier. I'm not so sure. I believe it is dependent upon the hardness/temper of the blade. What say you?
    Actually it has nothing to do with the hardness because your comparing one grind to another on the same chisel so the hardness will be a constant. On the same chisel a hollow grind may wear marginally faster than a flat grind, but in my mind it's not enough to worry about. However, if you've found a sharpening method you like that gives you good results, keep it. IMO, the most important thing about a sharpening method (other than that it works) is that it needs to be fast enough that you will do it consistently. If it's too big of a pain, then you tend to put it off until you absolutely have to. The point is to consistently have sharp chisels. If you let your chisel go dull because your sharpening method is a pain, then your method is no good. If your chisel stay sharp because you've got a workable method for you, then you're golden. I hope somewhere in my rambling I answered your question.
    Mark


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  4. #4
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    Re: Hollow Grind

    Style of Grind and hardness have absolutely nothing in common.

    Hardness is everything to do with the steel and the hardening process.

    As a matter of fact - some high quality Japanese chisels are only "case" hardened - leaving the "core" of the chisel soft (as steel is soft) and therefore has a "dampening" effect. You would NOT want to put a hollow grind on a Japanese Chisel - that would completely remove the exterior hardened surface.

    I don't put much stock into "hollow" grind - except where you need clearance on a cut. For instance is I could hollow grind my table saw blade - the sides would not "rub" when inside the cut.

    On a chisel? I don't see any advantage at all to a hollow grind.

    On something like a Tormek it would be HARD - NOT - to hollow grind.

    Soooo - Tormek, NEEDS, to - SELL - WHY - hollow grind is a good thing.

    Can you imagine Tormek pointing out that a hollow ground edge is weaker, and will dull faster?

    Sorry!!!!
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  5. #5
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    Re: Hollow Grind

    I agree with Stretch.

    Anyway I prefere a flat or hollow grind on my knives and even on some of my chisels and on my joinery axes. This is because the tool will ride on a flat bevel so it becomes easier to control.

    On my logging axes and on my mortise chisels I keep the bevel rather convex in order to make the edge stronger so that it will stand up to heavy use.

    On my double bevel broad axes I keep the bevels slightly convex so that the edge will cut out of the wood and leave a smooth wavy surface with as few splinters as possible.
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  6. #6
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    Re: Hollow Grind

    How does a hollow grind remove the hardened surface any more than a flat grind?

    I agree with stretch.
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  7. #7
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    Re: Hollow Grind

    Quote Originally Posted by ThisIsMatt View Post
    How does a hollow grind remove the hardened surface any more than a flat grind?
    In my post I said that some Japanese Chisels are case hardened. That means only the skin of the chisel is hardened. If you hollow grind that chisel - the hardened part will be removed and only the core will remain. The core would be as soft as non-hardened steel.

    Most chisels are made of a steel that will through harden. In that case - hollow grind will not matter.
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  8. #8
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    Re: Hollow Grind

    Wait a second ...

    Let's make sure we're all talking about the same thing ...

    Here's a Japanese chisel:
    Click image for larger version

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    I don't think anyone's talking about the hollow in the back of the chisel, but I believe THAT is ground, too. I'm sure we're talking about the bevel, but wouldn't grinding that back conflict with what Leo's saying?


    Also - how do you get a sharp cutting edge on the case hardened steel without cutting through the hardened skin?
    Jason Beam
    Sacramento, CA
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  9. #9
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    Re: Hollow Grind

    The case hardening would be done after the initial shape is made. Case hardening is generally no more than about .060 deep, more commonly around .030 deep. Either way, that is plenty deep enough to do the sharpening.

    Most chisels (99%) are make of a through hardening steel anyway.

    Maybe I should not have posted about case hardened steels - it seems to not fit neatly into this discussion.
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  10. #10
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    Re: Hollow Grind

    Considering that just about everybody is going to hone that edge on a flat stone or wheel; flat grind vs hollow grind has no impact on edge durability. A hollow ground edge can however be honed quicker because you need to remove less material to make the actual fine working edge. The geometry behind 1/64" from the final edge does not influence on edge durability in any way.


    My comment assumes that a fellow knows what final edge angle he needs and grinds accordingly.
    Dave

    Measure once... cut twice.
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