Elliptical flute shape

Discussion in 'Woodturning Discussion Forum' started by Dean Center, Sep 22, 2017.

  1. Dean Center

    Dean Center

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    At a recent symposium, Stuart Batty discussed flute shapes and emphasized the 'elliptical' shape as the best for his 40/40 grind. My impression was that this shape of flute is different from a parabolic cross section. Can someone explain how the two shapes compare? Or tell me I misunderstood and that they're really the same.
     
  2. Bill Boehme

    Bill Boehme Administrator Staff Member

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    They're so close at the size we're talking about that it is meaningless to get mired down in the minutiae of difference between the two. Besides, once the flute has been polished to remove the machine marks, the flute will be neither parabolic nor elliptical. There is not just a single shape for either a parabola or an ellipse, but a whole family of curves for each.

    It's a lot like golf clubs and fishing rods. We can get lost in the details and forget that it's the person holding the tool that makes the difference.
     
  3. robo hippy

    robo hippy

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    Pretty much what Bill said. I do prefer more open flutes to more closed/V flutes. This is probably because I hold my tools level when turning and cut with the nose rather than dropping the handle, so the more round the flute is, the better I like it. Doug Thompson's V flute is pretty open for a V, not like Glaser V which was really steep. I like his U flute as well. Stuart used to comment that the V flutes had a problem in sharpening because you always get a dip in the wing near the nose. This is because you need to hit the nose, then quickly flip it onto the side for the wing. If you roll at the same speed through the sharpening, you get that dip.

    I am really liking the parabolic flute shapes. Some times they just seem to cut better, and I don't know why. I use a 45/45 grind, compared to Stuart's 40/40, and don't use swept back gouges at all. I do like the V10 and M42 HSS for my tools. The edge holding difference between HSS and them is huge. Recently bought a 'signature' parabolic fluted gouge, and couldn't figure out why it got dull so quickly. M2.....

    robo hippy
     
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  4. Zach LaPerriere

    Zach LaPerriere

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    Bill and Robo hit it on the head, in my experience. I would add that I also like a wide open flute and I'm a fan of swept back gouges. I'm a sheer cutting fan, so I cut with my handle as low as the toolrest allows in many cases. I sharpen at 45-50°

    I recently picked up a 3/4" roughing gouge from D-Way. The flute is wide and deep, more than any other manufacturer I've seen. You can almost roll a regular marble down the flute. I love the steep wings for the sharp angle for both roughing and leaving a remarkably clean surface on my final roughing cut.
     
  5. john lucas

    john lucas

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    Absolutely Bill. Glen Lucas raved over how bad the V shaped gouges were. I've been using mine ever since Doug Thompson started selling them and love them. Yes you can get a dip in the edge when you grind it because of that shape so just grind more accurately. He based his opinion on how hard or easy it was for beginning students to achieve the proper grind. In my experience students can screw up any grind. It's more important to teach them how to properly shape tools with a grinder and develop that "touch". If you do that then flute shape doesn't matter. Far more important how you use the tool.
     
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  6. Bill Blasic

    Bill Blasic

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    I have been to and hosted many hands on and I have never seen a pro stop and say "I cannot use this tool because it is not a parabolic flute". A pro no matter what shtick they use to sell their own stuff can grab any flute shaped gouge and cut like you would not believe. They are masters of the cut of which tool shape means little. I myself cannot see any difference between Doug Thompson's V shape and a parabolic of another brand.
     
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  7. john lucas

    john lucas

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    I intend to buy a U shaped gouge from Doug one of these days so I can really compare. I do have a U shaped odd brand tool but it's not the same shape as Doug's U. The wings are really thin on that old gouge and that's really useful. I grind a long wing on that tool and then use it like a skew for the outside of bowls. I do a pull cut with the handle real low. You wouldn't believe how this tool cuts. Edge doesn't last long but it cuts great while it is sharp.
     
  8. robo hippy

    robo hippy

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    Doug's U flute doesn't take a swept back grind very well. Or at least when I used to use the swept back grind, I never could get a 'proper' shape with it. I have heard others comment the same thing, so it isn't just me. Well, I don't think so any way. I guess it does make an excellent BOB tool, but I prefer the fluteless gouges and detail gouges because I can roll them up on edge for a higher shear cut angle.

    John, students can screw up any grind, and so can I... Both Dave Schweitzer (D Way) and Doug do not make or sell the parabolic flute shapes for their gouges. Dave says more people have problems getting a proper grind on them. Doug feels that if you have a slight arc in the wing, it does the same thing as a parabolic shape. It dose look the same head on, but in use, it doesn't cut the same. No idea why...

    I have wondered about what it is about gouges for shear scraping and why some people prefer them rather than using scrapers like I do. I have been playing with a lot of variations of that lately. M42, V10, M2, honed, burnished, 600 grit burrs, and even totally honed off burr. I am guessing my reason for preference towards scrapers is that I don't have to roll the tool over so far. The only other difference I can think of is the gouge wing has a more acute tool angle than the scraper, say maybe 30/30 compared to 70/0 or is it 70/90?

    robo hippy
     
  9. Dean Center

    Dean Center

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    Out of curiosity, I took one of each brand of my bowl gouges and measured the wing angles. Which immediately created a problem. When one of the Superstars is advocating a particular angle, how do they measure? It's really hard to measure the actual angle of the steel, due to the short depth the flute allows, and also the angle changes if the flute has a curved shape on the side. So I also measured the angle of the wing referenced against the top of the flute. Given the concensus of previous comments that the shape of the flute isn't critical to you, this point may be moot, but which measurement do you suppose Stuart refers to in his 40/40 grind?

    Part two of my investigation was really surprising. I looked at each gouge end on to assess the shape of the flute. The selection of gouges in the study revealed my garage sale mentality, as I had a sample of Hurricane, P&N, Hamlet, Taylor, Thompson, and Crown. The shapes were all over the place, as were the widths and the depths. Since I am way more than 1 tool away from greatness, the variation might actually create a difference in my hands, when changing from one to another. The British tools were fairly similar in depth and shape of flute.

    I do notice that one of the tools cuts better for me than the others and 2 cut worse. The P&N has a very deep U shaped flute and has never felt right to me, but it makes a nice bottom feeder gouge. The other less comfortable gouge is Chinese M2 and I suspect the problem is that it dulls very quickly. My favorite gouge is a 3/8" powdered metal gouge, and it could simply be staying sharp longer or have less resistance due to the smaller size/shorter bevel.

    Writing this out, I realize what I should do--pick one brand and stick with it. But what if it's lack of M42 that's keeping me from greatness? I think you all should take up a collection so I can afford to buy a Baldor grinder with a pair of CBN wheels and a full quiver of ultramodern steel tools. I will do extensive research and report my findings.
     
  10. Bill Boehme

    Bill Boehme Administrator Staff Member

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    It's definitely the lack of M42 that stands between you and greatness. If you'll send me a self-addressed stamped envelope, I'll contribute two cents towards your very worthwhile goal.
     
  11. john lucas

    john lucas

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    Well I'm still testing but the type of metal doesn't change how sharp it gets. They all get to the same sharpness if you take the time to do it. Some do hold edges longer than others but of the high end tools, Cyrogenic, M42, V11 etc, it's pretty subtle. Ideally you should sharpen before they get that dull anyway.
     
  12. robo hippy

    robo hippy

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    Well, I have gone off the deep end with experimenting lately. Comments from Tom Wirsing, and watching Eric Loffstrom, and Stuart, and others.... For sure I will stick with either M42 or V10. I recently bought a 'name brand' parabolic fluted gouge to try out the flute shape. I did sharpen it to 'name' specs, and thought some thing was wrong with it because it didn't cut well for very long. A couple more sharpenings, and I figured out it was standard M2.... Huge difference in edge durability. I have said for years that the 'stays sharp 5 times longer' means that you get a 'working' edge for a much longer time, but I still prefer a fresh edge for finish cuts. One friend who has turned myrtle wood trays for 25 or so years at about 700 plus per year, said he couldn't tell any edge durability or sharpness differences between the two, which agreed with my findings. I have heard claims that one can be made sharper than the other, but never noticed it. It is more depending on how fine of a grit and honing you do than the metal. Some are easier to get to the scary sharp level than others.

    Then there are scraper burrs..... Eric made the comment that you get different burrs on V10 and M42. So, another whole round of experimenting. 80, 180, 600, 1000 grit, honed till there is no burr, honed till there is no burr and then burnished... Thus far, no significant difference between 80 and 180. Big difference going up to 600 and 1000, both of which are pretty similar. The burnished burr (I always do it by hand, not the Veritas burnisher thing which tends to 'overburnish') makes a far better/sharper edge for shear scraping than the others, and it is very durable, so will work for roughing. The totally honed scraper edge really is interesting in that it has a skew sharp edge, but not the included angles, but can leave a very clean surface in figured wood bowls, which is supposedly impossible even to me the scraper psycho. I have yet to put a micro/very light burnished burr to the test for the same cuts...

    Then there are negative rake scrapers.... Another animal.... Earlier thoughts were that I was cutting way past the live of the burr, and after a long phone talk with Tom Wirsing, "if you have to push at all, it is dull". 20/20 like Stuart? 22 1/2 by 22 1/2 like Tom? 33/33 like Glenn Lucas? About 60/30 with a burnished burr like Eric? The previous acute ones with a very light burnished burr.....

    Well, not is it out to the shop, or in to watch College football and play my guitar....

    robo hippy
     
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  13. Dennis J Gooding

    Dennis J Gooding

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    John, I do not know at what degree of sharpness it happens, but I understand that at some point grain size of the steel begins to limit the sharpness that can be achieved.
     
  14. odie

    odie

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    Good comment, Bill.......

    The one thing all flute shapes and different ways of grinding them is......they all have a cutting edge. If that cutting edge is presented to the wood well, it will cut well......and, like the other Bill mentioned: It has more to do with the hands that hold it, than anything else.

    -----odie-----
     
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  15. john lucas

    john lucas

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    Dennis At 5000X magnification you can start to see the structure of the steel. I just had 3 tools photographed to see which one is sharpest and they were so sharp we didn't see any difference until 2500X magnification. In Alan Lacers tests showing how honing improves the edge you could see the mountain peaks of the edge at 200X. On my edges at 1000X all you could see was still a straight edge. Going to have a Hunter Carbide tool that's brand new photographed in the next week or so. I thought it would be a good comparison because they come with a mirror looking edge straight from the factory.
     
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  16. Zach LaPerriere

    Zach LaPerriere

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    Great conversation. I agree to a point on the idea that flute shape doesn't matter.

    My take is that a particular flute shape enhances (or limits) a particular grind.

    The grind where flute shape matters most for me is the swept back grind, especially those with longer wings. By simplest definition, a cutting edge is the intersection of two planes. When I put a swept back grind on different shapes of flutes, the shape of the wings changes, both in geometry and angle of the cutting edge.

    Note that the cutting edge on the nose doesn't change. It's only on the wings, and again: the longer the wings, the greater the difference caused by flute shape further out on the wings. This is especially important for steep sheer cuts on final finish cuts.

    Background: I do much of my turning with a Michaelsen grind. When I go to finish a bowl, I sharpen (5) 1/2" gouges and (3) 3/8" gouges at a time, largely the same grind, because I like to swap out for sharp gouges without going back to the grinder. I've thrown parabolic, V, and U shaped gouges into the mix and I can tell over days or weeks which shape gouge cuts best, and which cuts cleanest. The difference isn't huge, and the difference is greatest on final finish cuts where my goal is to get the cleanest surface possible.

    Conclusion: There are a number of other factors which also change effectiveness of grinds: including flute finish (milling marks or polished), choice of sharpening wheels & grit, off-the-wheel or honed, etc. Most of these are differences between good and really good, and for most folks don't matter that much.
     
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  17. Bill Boehme

    Bill Boehme Administrator Staff Member

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    John, where did you get access to a microscope with that power?
     
  18. RichColvin

    RichColvin

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    The BESS machine is the best test method for sharpness.
     
  19. Paul Gilbert

    Paul Gilbert

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    I think that optical microscopes top out at 1000X and that requires oil emersion. By that I mean that you put the slide with a cover slip on the microscope table, put a drop of special oil on the slip and then put your objective lense in the oil. It would be a neat trick to do this with something like a gouge.

    With electron microscopy (with which I have no experience) I suppose that those type of pics are obtainable. One would need access to a big time lab and unless you knew someone the $$$ per image would be equally big time.
     
  20. john lucas

    john lucas

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    Bill It's a scanning electron microscope in a lab at Tennessee Tech where I used to work. One of my good friends runs the lab. I also now have access to a sharpness tester that I hope to use next week. All of this excess testing is beyond what is needed. What I started out to prove or disprove was that Carbon steel would get sharper than other steels and you couldn't sharpen Particle metal steels to a really sharp edge. Well I sharpened Carbon steel, HSS, and Particle metal steel to well beyond what we sharpen turning tools and probably at least as sharp if not more so than carving tools. All 3 cut the same as near as I can tell. That's why I went to the scanning microscope to actually see if there was a difference. More testing to be done in the next few weeks.
     
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