Warped Bowl Turning

Discussion in 'Woodturning Discussion Forum' started by Lamar Wright, Oct 19, 2017.

  1. Dennis J Gooding

    Dennis J Gooding

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    That should work well Gary, particularly for bowls that have shrunk symmetrically. However, sometimes you may encounter ones that are badly distorted, e.g., crotches or blanks cut from tension wood. In those cases, lining up the rims may not yield the best bowl, and you need an initial mounting method that gives you more flexibility for adjustment. As a production bowl turner, Glenn Lucas probably would have tossed those pieces.
     
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  2. Lamar Wright

    Lamar Wright

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    Dennis it seems to me that maple wood distorts badly or is it just me? My first green maple bowls that I rough turned air dried in 3 months in a humidity controlled atmosphere...... I don't know if that soon of drying time had anything to do with major warping?
     
  3. Gary Beasley

    Gary Beasley

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    Glenn made mention of that and was of the opinion the asymmetrical bowl can be saved with this jig. Most likely depends on how bad off they are. Would love to see him do that at some point.
     
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  4. Lamar Wright

    Lamar Wright

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    That would be great to see how Glenn does it.
     
  5. Dennis J Gooding

    Dennis J Gooding

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    One possibility, if you can establish that one lobe of the bowl is too long, is to saw or turn off a bit of it and try again. Repeat as necessary.
     
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  6. hockenbery

    hockenbery AAW Advisor Staff Member

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    I try to get symmetrical grain in twice turned bowls.
    This of course produces symmetrical warp.
    It also generally produces the most pleasing grain pattern in the bottom of the bowl.
    It also has a high success rate in drying.

    I cut my blanks from the centers of half logs and I align the grain when roughing.

    Crotch grain I turn as natural edge bowl and let it warp into more pleasing shapes
    It will warp with symmetry if the two branches have near equal diameter however the warp symmetry is rarely centered on the center of the bowl like it is with straight grained wood.
     
  7. Lamar Wright

    Lamar Wright

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    After trying many methods of turning a warped bowl, I found out what works best for me it to use my faceplate mounted to the inside of the bowl and work on the foot and outside of the bowl first. After the bowl is round I then mount the bowl to the tenon/mortise and work the inside of the bowl. I guess turners have find out what works best for them. Thank you all for your comments and ideas.
     
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  8. Owen Lowe

    Owen Lowe

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    Lamar, are you actually screwing the faceplate to the inside? I use the tailstock to apply pressure against a chuck that’s inside the bowl — friction driving it to clean up the tenon — then flip the bowl around and use the chuck to grip. Because the warping also affects the inside bottom, a small contact area isn’t affected as much as a large one. Since I’m only cleaning up the tenon, the inside contact supports that small area.
     
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  9. Lamar Wright

    Lamar Wright

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    Hi Owen, yes, what I do is when I turn a green bowl I always leave enough thickness inside the bowl to mount the FP with #10 wood screws knowing that when I clean up the inside of the bowl will take care of the screw holes. I adjust the FP to where the bowl turns the smoothest without a lot of wobble. It works for me, however, your method sounds good to me! Does the tailstock get in your way cleaning the tenon up?
     
  10. hockenbery

    hockenbery AAW Advisor Staff Member

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    Lamar I do much the same thing as Owen describes. I also shape therm and the outside of the bowl when it is jam chucked over a chuck with the jaws open a bit. You could use this method to just true the tenon.

    Anything that works is fine but when you leave wood for screws you need a thick bottom.
    I generally turn the bottoms of my roughouts a little thinner that the sides which helps in drying.
    And this leaves no wood for screws

    To see the tenon being shaped
    Fast forward to 15:41 and you can see the tenon being trued with the tailstock in place.
    Mounting and turning a dried bowl -
    View: http://www.youtube.com/watch?v=sCZWsHB4vlM
     
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  11. Lamar Wright

    Lamar Wright

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    Hi AL, I see what you and Owen were talking about using an expansion chuck to hold the bowl in place. As you said in your Demo video, it is a lot faster to use your method. My tenon was a lot more warped than the bowl in your video. I see though how you trued the tenon with the tailstock in place. Simple and easy. I have several green bowls that should to turn in several months and I'll sure true them with your method. Being new to bowl turning I was a little reluctant using the chuck thinking the bowl might come off. Using enough pressure from the tailstock against the chuck I see now that there is no reason the bowl should come off. Thanks Al.
     
  12. hockenbery

    hockenbery AAW Advisor Staff Member

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    As long as you have a tailstock that locks in place well and have solid wood, turning between centers and jamb chucking over a chuck are stronger ways to mount wood than a chuck.

    I leave the center point from roughing in the tenon. This is a good center to use for bowls with balanced grain.
    If I don’t have a center point the tenon will be an ellipse shape. I find the midpoints of the long axis and the short axis of the ellipse and use that.
     
  13. Owen Lowe

    Owen Lowe

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    As Al commented, a screw-attached faceplate on the inside requires leaving a fair bit of extra-extra bottom thickness. I’d be concerned about really long drying times and cracking developing due to the thickness. I routinely follow a 10% wall and 7% bottom guideline for rough-out thickness for side grain bowls. (A 14” bowl gets about 1.4” for wall thickness and about 1” in the bottom with a blend between the two.) The bottom will not warp to anywhere near the degree the sides will, so can be markedly thinner. Both calculations allow interior and exterior cleanup and refining. It works for me, the woods I use, and my drying conditions.

    For re-truing the tenon, I am really only concerned with the roundness of the tenon and the consistent squareness of where it meets the bowl exterior (where the chuck’s jaws contact the main body of the bowl). The tenons are generally 3-4.5 inches in diameter, so I’m not usually fighting for space with the tailstock. I use a combination of spindle gouge, bedan, and/or scraper to get things round and square. My goal is to remove as little as will get things true so that a lot of support is maintained for reworking the bowl.
     
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  14. Lamar Wright

    Lamar Wright

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    The bowl that I was working with (when dried) had a lot of shrinkage and it was a small bowl ( 5" ) warped to almost to an oval shape. No cracks just warped real bad. Being new to bowl turning this was my first bowl that dried enough (Maple 9% MC) to turn. The tenon was small (2.5"). I've learned a lot since turning that bowl. After finishing the bowl the OD was 4.2". Green bowls I turn now I follow the 10% rule. I should have some Maple and Cherry rough turned bowls dry enough to turn in a few months and I will use the expansion chuck method rather than using the FP. I have learned to turn the tenon a little larger also. Thanks Owen for you and also Als ideas on how you turn your green bowls. I don't leave the bottom of the bowls as thick as I did since I will be using the chuck.
     
  15. Jamie Straw

    Jamie Straw

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    He mentioned in his Seattle demo that on a large bowl, the tenon can, indeed, warp off-center to the bowl. I guess if you turn a couple or three thousand bowls per year, you need a really quick way of centering these bowls Here's a picture of the demo slide-show that shows a bowl mounted (thought it doesn't seem severely warped).
    Lucas Warped BowlRdx.jpg
     
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  16. john lucas

    john lucas

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    In my early days I made a lot of bowls without paying much attention to grain orientation. symmetrical grain orientation usually leaves a bowl so the warp is symmetrical as Al said. If the grain isn't balanced then the bowl warps all kinds of funny ways and will also through the tenon off. I used to use a large wooden faceplate with lined drawn on it. I would center the outer rim of the bowl on this as best I could and then turn the tenon true by using the tailstock. I found that I had to remove the center pin of a cupped tailstock to be able to fine adjust the centering. I turn the bottom plus the tenon the same thickness as the sides to help it dry more evenly and not crack. The bottom doesn't warp as much so you can get away with that. I think John Jordan is the one who told me that and saved me a lot of headaches.
     
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