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Thread: little bit of tool theory

  1. #1
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    little bit of tool theory

    Well, I went to turning and hand tool seminars at the recent woodworking show co-located with Totally Turning this past weekend.

    While playing on the lathe this week I had a thought. Does looking at the angle of attack that a cutting tool makes with the tangent of the round turned object as if the cutting tool were a plane iron have any usefulness? At one of the seminars I went to, I learned that low angle planes need less force to cut, but that high angle planes tend to leave a better finish.

    Is there any usefulness in maybe using a low angle of attack tool for rough shaping and then using a high angle of attack tool for a finishing cut?

  2. #2
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    I'm not much of a turner, but I think I know what you mean.

    The thing I've been working on is really 'riding the bevel'. Seems like everything I read stresses this. When I do manage to do that, things work pretty well.

    if I raise my angle of attack, I can sure hog shavings off faster, but its not as smooth, and I risk a blow out causing catch...

    Still working on my technique...
    Programmer - An organism that turns coffee into software.
    If all your friends are exactly like you, What an un-interesting life it must be.
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  3. #3
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    Mark,
    Very interesting thoughts.
    In hand planes, the sole controls the bevel angle. In low angle block plane, the blade is inserted upside down, so we know the blade bevel is not the controlling bevel like most of the turning tools. Except Bedan with bevel up, riding on the whole bevel of the flat side of the tool. Most like you will get a catch when that big bevel is off.
    In wood turning tool, the primary tool grind angle is the only control we can have. If we get off that, there won't be control until we get into other cutting modes.
    We can also rotate the tool presentation skewness angle to change the effective cutting angle. We can get a cleaner cut if the effective angle is lower.
    In regular scraping mode, the tool edge is at a higher angle than the bevel gliding mode. That is the roughing cut in turning.
    When we rotate the flute almost facing the blank, with handle down in shear scraping made, that is one of the finishing cuts. That is an extreme high angle. With the handle down, we are trying to get a lower skew angle.
    Gordon

  4. #4
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    I was kind of thinking that all lathe cutting tools are like a bevel up plane. If I want to mimic a high angle plane with my LN #62 Jack, I need to put a different iron in it that is sharpened to a different bevel angle. Analogously, instead of using the same tool differently (i.e. off the bevel), if I wanted to change my angle of attack on the lathe I would need to use a differently ground tool.

    So, does anyone ever change between different bevel grinds of otherwise the same (or very similar) shape tool for different turning situations? Or does having multiple very similar shapes tools differering primarily in bevel grind drift into the independantly wealthy socioeconomic status?

    I think maybe I wasn't this clear in my first post.

  5. #5
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    Mark, there are some turners to have similar gouges with different grinds for different applications. Although it's not really quite the same, but I know I use my V shape gouges for different things than I use the U shaped ones for. I don't know what angles any of my tools are sharpened to, and I don't really pay much attention to the minutiae of how the bevel interacts with the wood. I just turn the tool to where it's cutting the way I want and go from there. After a while, the gouge seemed to become second nature.

    It's good to understand how it all works, but don't get too bogged down in the details. When I was teaching guitar, I had a few students who tried to overthink everything, and it usually got in the way of them being able to play the instrument. One of my beginning students was a hand surgeon, and he spent so much time trying to analyze the physiology of why it was difficult for him to change from one chord to the next, that he never did figure out how to change chords. All he really needed was the repetition of doing it over and over so the muscle memory could take over.
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

    workingwoods.com

  6. #6
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    Mark,

    Dale Nish explained the different gouge angles here:
    http://www.woodturningdesign.com/askdale/14/14.shtml
    Gordon

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