Taking fine cuts inside a bowl...

Discussion in 'Newbie' started by Jamie Straw, May 31, 2016.

  1. Jamie Straw

    Jamie Straw

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    Found myself betwixt and between today, making finishing cuts on the 10.5" Madrona bowl. Really had some bad tool marks after choosing the wrong gouge, then couldn't seem to get the right combination for a fine cut that would only remove tool marks and a bare shaving of the smoother wood. Didn't seem appropriate for a scraper, kinda between a scraper and a gouge. The worst marks were in the flattish bottom of the bowl (~2-1/2"+), so I switched from the bowl gouge to a bottom-of-the-bowl gouge. Oy! Didn't handle well on this shape, way too aggressive (I've loved it on other, smaller, deeper bowls). Went to a smaller BOTB gouge, that worked a bit better. Ended up using the scraper waaaayyyy more than seems sensible.

    I'm sanding now, but any advice would help for the next one. This bowl has been a real challenge. Here I thought than a shallower, wide bowl would be so much easier. Not. Might be the wood, which is pretty hard, but I sense that there's something else making it a new experience.
     
  2. hockenbery

    hockenbery AAW Advisor Staff Member

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    The inside of dried bowl is a bit of a challenge. Because of the up interupted cut caused by the warp.
    I try to take several small controlled cuts ( instead of one big one) to get the first 1-2 inches of the inside wall round.

    I find a 1/4" bowl gouge with a Michelson grind does a great job in smoothing the first inch or two of the wall.
    The bevel riding cuts the rest if the way to the

    The hemispherical bowls are likely the easiest overall to hollow.
    The cuts are arcs and the curve runs from the rim to the bottom center.
    With That continuous curve I am always cutting across fibers and get a clean cut.

    issue with wide bowls it is difficult to make the continuous curve and we end with a flat bottom.
    The gouge is cutting straight into endgrain twice a revolution

    Also it is harder to keep the bevel on flat than it is to keep,it on a curve.
    Often it I easier to use a scraper on a wide level bottom.

    If you have the opportunity to have some one tech you the flute up shear cut it makes inside surfaces smooth
     
    Last edited: May 31, 2016
  3. robo hippy

    robo hippy

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    I don't like the bevel rubbed finish cut, as Jimmy Clewes commented, 'it burnishes the wood, and first thing you have to do when sanding is to cut through the burnishing.' Some days, the cuts through the inside go smooth and easy. On days when they don't, the NRS (negative rake scraper) is becoming my favorite tool. Anything to save on sanding time... For your BOB tools, the fluteless gouge takes off the least or finest shavings, and the others, because they have flutes, can dig in a bit deeper. You are the one that controls the cut. If you are getting a bit tired, that does make things go less smooth...

    robo hippy
     
  4. hockenbery

    hockenbery AAW Advisor Staff Member

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    The bevel can burnish the wood if you push it against the surface.
    If you are burnishing the wood you have too much pressure on the bevel
    Let the bevel float over the wood just close enough to support the cut.

    Shortening the bevel by grinding off the heel reduces bevel contact more
    The advanced shear cut technique with flute up has almost no bevel contact.

    The Michelson grind has a very short micro bevel. Does not burnish.

    When just learning it is better to rub a tiny bit more than needed, than it is to let the tool come off the bevel.
    Rub too much and the gouge won't cut or it make chatter.
     
    Last edited: Aug 4, 2016
  5. Jamie Straw

    Jamie Straw

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    I was being very careful about the bevel, burnishing wasn't the problem. To get the right approach, I adopted,, some time ago, the imagery of riding the bevel as one would ride a wave. All gouge heels have been ground back for some time now, but have yet to try a micro-bevel.
     
  6. john lucas

    john lucas

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    If you grind off the bottom of the bevel it reduces the burnishing tremendously. Also trying to glide the bevel instead of push on it as Al said.
     
  7. Jamie Straw

    Jamie Straw

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    Hmmmm, you must have missed my 8:49 AM post? "I was being very careful about the bevel, burnishing wasn't the problem. To get the right approach, I adopted,, some time ago, the imagery of riding the bevel as one would ride a wave. All gouge heels have been ground back for some time now, but have yet to try a micro-bevel." You see, I pay attention to the basics!:) Hey, John, if you have time, check your messages -- I sent a ? about the aluminum wheels.
     
  8. John K Jordan

    John K Jordan

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    This is one area I rely on hand scraping with the small card scrapers, mostly with the grain, lathe off. One with a very gradual curve is good for mostly flat areas. Sometimes I unscrew the chuck from the lathe and sit to finish. Very little sanding required. I have found nothing easier or quicker to get a perfect bottom center.

    JKJ
     
  9. Jamie Straw

    Jamie Straw

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    I suspect there'll come a time when I'd like to try that, John. When I was flat-woodworking, I played with a card scraper just a little bit, but would have to invest in the smaller scrapers. Do you have a favorite source?
     
  10. John K Jordan

    John K Jordan

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    I have three kinds: the first one I cut from a larger scraper with a Dremel.
    scraper_PB054025_s.jpg

    I found a set of small curved scrapers at Highland Hardware in Atlanta (now Highland Woodworking). I can spend $1000/hour in that store. Ack.
    Years later I found another set of mini scrapers at Woodcraft. I see them in the online catalog, Lynx brand I think.
    The smaller scrapers are good for inside curves and outside coves (with lathe spinning) but are thinner and don't seem to hold an edge as long.

    Somewhere I found a set of full-sized scrapers that included two with gentle radii on the long edges. The are perfect for many shallow bowls, wings, and the center bottoms of things.

    I grind new profiles from large card scrapers as needed. The higher quality scrapers used by fine cabinetmakers are the best, probably because the steel is better. I bought another stack of old flat-work card scrapers for a few bucks just last week which I'll cut and grind into some smaller shapes. Note that these are probably carbon steel and not HSS so you have to be careful not to overheat them when grinding.

    I've posted this picture before, but here are some of what I use:
    scrapers_.jpg

    Once I got more proficient at using scrapers to remove tool marks (and tearout) I quit using the rotary drill for power sanding. There is far less fine dust in my shop. There is also the zen factor: spending some quiet, relaxing time in a comfortable chair with soft blues playing, glass of iced tea at hand instead of standing at the lathe with a respirator and face shield making a cloud of dust!

    JKJ
     
  11. odie

    odie

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    Everyone who has given advice in this thread, are very capable woodturners......and each of them are getting great results on their own turnings by varied methods.

    As of late, I'm basically using the "micro bevel" on a standard bowl gouge. The very steep angle of the Mahoney style bottom feeder does work, but I think it works better for an interior that has a long continuous curve. For bowls that intentionally have a flat, or flat-ish bottom transitioning into very pronounced curves towards the sides, I'm leaning toward a bowl gouge with the micro bevel. The bevel is lightly rubbing just enough to guide the cut. (I know you get that, Jamie.) It's generally a push cut from close to the rim, and around the curvature of the sides......which becomes a pull cut as it transitions toward the flat central area of the bottom. For more initial shaping of the interior, the push cut can go all the way to the very center, but it's a bit more difficult to control well. The pull cut at the bottom center leaves a surface that is more refined, with less sanding. There will still be a need for some aggressive sanding in the interior, but with much less need for leveling little ridges and valleys......which really decreases the time needed for the initial coarse grit.

    Other things need to work in harmony to get the best cut possible. The gouge needs to slide smoothly across the top of the tool rest. This can be enhanced by doing your own polishing of both the gouge and tool rest. Your grip on the tool needs to be light and with dexterity.....your muscles need to be loose, fluid, and relaxed......so that everything is working in harmony, and the tool "flows" through the cut. This can be a problem if there is the slightest catch. A catch can dangerously fling your tool out of your hands......so knowledge of how to avoid catches is stressed. Also.....needless to say......the sharper your cutting edge, the better the results.

    I don't worry about the little bump at the very center of the bottom/interior.....as long as it is above the surrounding surface, and not a "divot". Sanding this bump is how I take care of it, and it's easy to do with a disc. As always, it does take a little practice to keep the bump from becoming a divot......but, I'm confident just about everyone can learn this technique with a minimum of effort. The concept is simple......practice is the key to success.

    ko
     
  12. Jamie Straw

    Jamie Straw

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    Thanks for your detailed description, Odie. Two questions:
    • How far around the nose/sides of the sharpened part of the gouge does the micro-bevel go?
    • My mental walk-through stumbles on the pull-cut part. More detail there - how does that work? Wonder if we could incorporate Skype into the new forum.:D
     
  13. MichaelMouse

    MichaelMouse

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    Check out this interesting article on edge versus wood. http://homepages.sover.net/~nichael/nlc-wood/chapters/caop.html Notice I said edge, so that people won't get hung up on the word "plane." Your "micro bevel" or shortened bevel or other suggestions adjust your clearance angle, which means the heel won't bounce and burnish. They can also modify your pitch angle which results in a greater percentage of scrape than slice, which can be used, if you have the steady hand, to produce see-through shavings.

    OR you could take advantage of another phenomenon, that of a longer bevel (decreased sharpness angle) combined with a very small pitch angle. You could combine this with an even lower effective pitch angle by skewing the edge to the work. The smoother the slice, the smoother the surface. Edge is a bit more fragile, which means if you turn it broad in like a scraper it won't last long, but keeping the rest tight and the off hand heavy on the tool will prevent that. Works best with gouges like the old bowl makers used, if you have one around. Broader the sweep, the greater the possible skew and the lower the pitch angle.

    3/4" wide gouge taking excelsior shavings. http://i35.photobucket.com/albums/d160/GoodOnesGone/InsideTrim.jpg
    Orientation of gouge and a view of that area above it that tears out when you're too wide in the cut. Yellow birch, which is really prone to tear, and none showing. http://i35.photobucket.com/albums/d160/GoodOnesGone/Frame-From-MVI_1017.jpg

    Action leveling then smoothing with the same gouge shows a couple of interesting points. First, the combination shear/skew angle being varied as the surface approaches true. Second, the swing entry performed by the control hand, where the tool does not move along the rest until the proper angle is obtained, as evidenced by the shaving. Frank Pain was right when he said the wood teaches you how to turn. http://vid35.photobucket.com/albums/d160/GoodOnesGone/TrueBottom.mp4
     
  14. Gerald Lawrence

    Gerald Lawrence

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    Don't know about Odie, but one of the French demonstrators (Yann Marot) who is an instructor at the Escolen school in France, uses a 35 degree bevel on his spindle gouges and it is less than 1/16 inch . He uses this to clean up cuts and it was very effective
     
  15. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I did a double take before I figured out that you weren't talking about intentionally dulling the edge although if used improperly as you said, that would be the result. :D
     
  16. odie

    odie

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    I'm currently on vacation, and am having some difficulty using someone else's borrowed laptop.......

    The entire interior surface can be done with the same deep flute bowl gouge, and I suspect it's ground similarly to the French demonstrator's spindle gouge Gerald mentioned above. Regardless, it's a very narrow strip where the angle changes slightly from the original grind of the heel.

    Jamie, it's hard to know what it is you are visualizing with my description above pursuing this cut throughout the entire interior surface......but, in case you are thinking that the cut transitions from a push cut, to a pull cut with one continual sweep......it doesn't. At that point where it's decided to switch, a whole new grip and setting of the tool rest will be necessary to continue. Most of the innermost part of the interior can be done entirely with continued removal of material with the push cut over the entire surface....up until that point where you decide to continue with a more refined cut in the flat area of the interior. THEN, it can be pursued with the more refined pull cut.......

    ko
     
    Last edited: Jun 16, 2016
  17. Jamie Straw

    Jamie Straw

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    Gotcha, thanks! It was the part "which becomes a pull cut as it transitions...." that confused me.
     
  18. odie

    odie

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    My fault.....I try to be as descriptive as I can make words be, and in doing so, I make some pretty obvious mistakes sometimes!......and, I probably won't win any awards for my proof reading either......:D
     
  19. Douglas Ladendorf

    Douglas Ladendorf

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    Your not the only one. I thought it was some sort of tool work Jujitsu! o_O
     
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  20. Breck Whitworth

    Breck Whitworth

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    Jamie I will add my two cents here and hope it will help on future bowls. When finishing a dried bowl think of the process as two stages. The first stage is what I call my initial rough cuts. This is where I take the bowl to it's final shape,depth and wall thickness, not really worrying about tool marks. The second step is the most important step to prevent having to use sand paper so much.(Please remember sand paper is a cutting tool and the final product doesn't tell anyone how it got to be so beautiful)(chuckle) Before I start my second step I go back and sharpen my bowl gouge again. Then I turn up the speed faster than I used on the first process. One of the most important things to remember here is to take light cuts and slow down. With practice you will quickly find that just by resharpening before the last few passes will help greatly. The increased speed makes the gouge flow smoothly and cut easier. Taking light cuts with smaller curlies also helps. Good luck
     
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