The Varigrind Jig Is Adjusted, Now What?

Discussion in 'Woodturning Discussion Forum' started by Dennis J Gooding, Feb 23, 2017.

  1. Dennis J Gooding

    Dennis J Gooding

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    John Murphy's thread on the geometry of gouge sharpening has grown long and has meandered into the issue of how to use the the jig after it is set. I would like to throw in another consideration that may draw it out even further. Glenn Lucas, in his DVD on Sharpening Techniques, points out that special problems arise when trying to grind wings on bowl gouges with V or U profiles, and that the parabolic profile is to be preferred when using jig sharpening. The issues that he describes sound a bit like what Grant Wilkinson mentioned. :personally, I have only parabolic flutes in my arsenal so I am not in a position to experiment. Have others faced this issue?
     
  2. Grant Wilkinson

    Grant Wilkinson

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    Dennis: I promise that I won't take this one off kilter. I'll only say that my gouges are primarily V shape Thompson's.
     
  3. hockenbery

    hockenbery AAW Advisor Staff Member

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    I prefer the parabolic flutes. I use the Ellsworth grind or at least my version of it.
    I have a Thompson v and don't like it.
    I have a Jamieson gouge made by Thompson that I love.
    The v has little usable shoulder and it does not do the flute up shear cuts well or have much of a sweet spot for the push cut.
    The Jamieson is a dream to use flute up or in the push cut.

    So I just use the Thompson v for roughing cuts and the pull cut which it works well for.
    Then I use one of my parabolic gouges for push cuts and shear cuts.

    I haven't seen much issue with sharpening a v gouge with a jig other than it is their nature to be pointy and it is easy to grind the tip too much.
     
    Last edited: Feb 23, 2017
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  4. john lucas

    john lucas

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    When I first started using jigs like the Ellsworth and Wolverine I had problems similar to what Glen Lucas describes. You get a small dip in certain sections depending on how the flute is ground. I quickly got over it. You don't grind with the same pressure from one side to the other. You grind where you need to and use light pressure where you don't. I've been using a Thompson V for many years and love it. I guess I just learned to use it.
     
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  5. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Everybody uses the term parabolic flutes, but I think that they are elliptical. :) I would like to see how they are ground.
     
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  6. Gerald Lawrence

    Gerald Lawrence

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    I agree with John that the Thompson v works fine for me. Yeas it is easy to geta miss grind on the nose, but you learn to work around it. Ain't it wonderful to all agree on something......;););)
     
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  7. Dennis J Gooding

    Dennis J Gooding

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    By Jove, you are right Bill. The tips of all skinny ellipses start out as parabolas and visa versa. Then they slowly diverge. I expect that you could not measure the difference between the two over the small depth of a gouge flute!
     
  8. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Dennis, I was sort of hoping and expecting that you are another engineer or mathematician would respond. My post was a bit tongue-in-cheek because the difference between the two is so slight. Depending on how the stock is milled, it might be easier to mill an ellipse. Of course, it is also possible that the flute shape is neither elliptical nor parabolic, but something else that is the result of polishing out milling marks. I think that if we delve deeply into mathematically precise descriptions for the various flute shapes, I would like to offer up three flute categories: skinny, medium, and fat.
     
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  9. Jon Murphy

    Jon Murphy

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    Aha Dennis, I found you <grin>. I take no blame for the diversion of the meandering of the thread.

    I beg indulgence if I become hyperbolic, or use circular reasoning, but I fully concur with you and Bill on the matter of flute shape. The progression of conic sections from the perfect circle to the ellipse, then to the parabola, and finally to the hyperbola is continuous as the angle of the section to the cone progresses from the horizontal (assuming a cone axis oriented vertically). As I think of it I realize that a V is also a conic section, but a special one that is a hyperbola oriented on the axis if the cone and coincident with it.

    As you and Bill both know, the circle and the ellipse are complete within the cone, they come to closure - and the parabola and hyperbola both exit the cone and diverge forever. To be exact, the parabola and ellipse are never the same - even at the skinny tip - but they can be so close there is no way to tell the difference.

    A U is another thing, it is a half a circle then a couple of straight lines - it is a construction, not a conic section. OK, another chapter of Murph Says - but the real point is that you are both quite right that the exact nature of the curve of the "superflute" is undefined. Is it an incomplete ellipse or a parabola? Who cares. It is a smooth curve of gradually changing shape.

    I think it is a parabola, looking at my tools and doing an eyeball extension - but it could easily be the end of an ellipse that I can't picture.

    That said, may I add that I'm still convinced that the leg angle should vary to make the same side grind shape with different tip bevels. Dennis's two angles, A and B are not the only angles. I just haven't figured out how to describe it clearly. I started my thread on the geometry as a proposal, and that because I couldn't find a way to measure the angle of the grind on the wings. I think I've found one, but have to experiment more.
     
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  10. Emiliano Achaval

    Emiliano Achaval

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    I have noticed that turners get used to whatever they grind. I have seen some really strange grinds, yet somehow the turner adapts to it... Beginners bring their tools to me to resharpen. Problem is, their set up is different than mine, so when they go back to their shop... I used to recommend the Don Geiger old system, but now he doesn't sell it anymore. He does have something new, that I dont know how it works. With the old one, was easy to reproduce the height and distance... To me it was harder to learn how to sharpen than to turn, we didn't have internet with you tube then...
     
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  11. odie

    odie

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    Here are a couple of significant statements made in this thread:
    It's true! The speed at which one learns is much determined by the time and effort one puts into "shop time"......multiplied by any one's ability to observe, comprehend, retain, and repeat little things that work well. Gather up enough of these little observations into a bundle of knowledge, and you have a turner who gets results that are noticeable, and distinctive.
    Right.....who cares? Well, I guess some people do, but is dwelling on descriptive language that which produces physical results in the shop? I think not. To be correct, though......there must be some means of passing thoughts accurately between individuals, and it's difficult to do that without using the (most) correct words. In this particular case, Jon is right, in that the curvature of the flute need not be described accurately, because words are pretty useless means of describing how to use that flute shape, once the gouge is in your hands and applied to wood. Big differences might mean a lot, but here, we're attempting to describe minor details which make little difference in practical application. Not only that, but each piece of wood is different, cuts different, and we all need to learn to adapt on the go!......

    -----odie-----
     
    Last edited: Sep 6, 2017
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  12. hockenbery

    hockenbery AAW Advisor Staff Member

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    I see a a fair number of post beginner turners limited by their poor sharpening. They somehow learned to use a gouge with dips in edge with occasional catches. When I hand them a gouge with a Convex edge they improve their turning instantly.

    I have Don's old vertical solution system works great.

    I have been playing with his new "Evolution" system.
    It is quite a slick way to set up the standard vee arm and varigrind to sharpen gouges.
    Easy to relieve the bevel or add a micro bevel.

    Don is a distant neighbor about 2 hours away. The guy is sharpening wizard.
     
  13. John Torchick

    John Torchick

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    Interesting thread with information that I'm not familiar with as a newbie. Need to do some homework.
    Would the variations in tool grinds be something that started out as an experiment- What would it do if I ground the tool this way?
    I have learned that it is necessary to keep tools sharp in order to have a good finish and lees effort at cutting contours, angles, etc. My grider is about two steps from the lathe. I keep the Wolverine set for whatever tool I am using.
     
  14. Emiliano Achaval

    Emiliano Achaval

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    I couldn't remember the name last night, "Vertical Solution" I love it... I would like to try his new system, but I dont want to spend the money... He emailed me to tell me about the new system, I had recommended the vertical solution to 2 turners, both called me back to tell me he didn't sell it anymore! Don said David Ellsworth had call him too about it...
     
  15. Jon Murphy

    Jon Murphy

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    Dennis, it seems meandering is generic to the Forum - I'll try to come back to your original question. I haven't seen Glenn's DVD, nor Grant's comments, but it seems to me that the continuously changing curve of the parabolic (or partial ellipse) flute shape is a match for the continuously changing grind angle when using a jig and making "long" wings. As I picture the process it seems that the wings on a V would change angle more rapidly that on a parabolic when using a jig. A hand grinder could compensate for that, but that is beyond my skills.

    Oops, just saw John Lucas' post in this thread - what he describes is what I was guessing at. I guess the answer is that if you can compensate for the straight sides of the V then keep on using it, but if you haven't learned how to do that yet go with the parabolic.

    I do have a couple of Thompson U gouges that I grind as "bottom feeders" - a tip bevel of about 80 dgs. and very short wings - but they are "specialty" tools for me.

    I "tugs me forelock, respectful" to Odie. Adapt on the go, learn to use your tools in different woods. But it is a lot easier to do that if the curve of the grind changes consistently along the wings, and I think the parabolic makes it easier to maintain that with a jig.

    The meandering has started with the mention of Don Geiger's vertical system, so I'll add to it. I had bought his original about six months before he came out with the improved one (the one with a pin to set four different fixed distances given the same setting of the main arm). Don was kind enough to sell me parts to make the conversion, and I made a few of my own modifications. It is a gem - I can duplicate my grinds in two passes (more if I've done a lot of honing). I've looked at the instructions on the Evolution and it appears it performs the same function for a lot less money - at least for most turners.

    I'm sorry Don has dropped the VS, and seems also to have dropped his "centering solution". I agree with Hockenberry, he is a genius in devising devices for sharpening - but also for other things. The Centering Solution is a drill guide that screws into the threading of your chuck or face plate so you can drill a hole (I think about 3/8 or so) into the tenon of a bowl. With it is a plug that fits into the hole, and rides in a revolving tail stock center. Actually only tapered one's like Oneway, but I got a discount from Don to not take his plug and made my own out of aluminum stock. Using the plug shoved about 7/16' deep into the tenon I can recenter a bowl on a jam chuck that isn't a close fit in about two minutes, and sometimes it is perfect the first try. It used to take me a half hour using a pin center. And I no longer have wish I had space and money for a vacuum chuck.

    OK, digression - but I wanted to support Hockenberry's compliments to Don Geiger, whose devices save money and time and actually work.

    Best, Jon
     
  16. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I am very pleased to see that you used the correct terminology "jam" vice the homophone "jamb" with reference to chucking. The use of the word "jamb" seems to have gained an unbreakable toehold and like "normalcy" may eventually become regarded as normal. Saving the English language from such kinds of mangling is probably a lost cause, but I shan't cease fighting on. I apologize for the diversion and return this thread to its prior direction.
     
  17. john lucas

    john lucas

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    I was going to use a Jamb chuck to make tendon on my bowl.
     
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  18. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Arrrrgh! :D

    Yes, tenon vs. tendon is another lost cause. :(

    BTW, I pulled a tenon in my elbow while putting a tendon on the bottom of a bowl. :rolleyes:
     
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  19. john lucas

    john lucas

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    I'm still confused about Rebate and Mortise. Is there a difference. Is it a mortise if it's flat work and rebate if it's a turning.
     
  20. Gerald Lawrence

    Gerald Lawrence

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    Bill according to Capt Eddie Tendon was in the old text books and yes I agree with you ,but maybe it is just the way it is.
     

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