Warped Bowl Turning

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

  1. Lamar Wright

    Lamar Wright

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    Hello turners, I have some maple bowls that has dried enough to turn( 9% MC ). I rough turned them 3/4 " thick and no checking just warped as I expected. This will be my first experience to turn a warped bowl and I was wondering what is the best approach to turn a warped bowl?

    My new 1640 is all set up and ready to go. These bowls will be the first bowls turned on my new Jet lathe. I was supprised how heavy this lathe is and very stable. The rotating head works flawlessly. Will come in handy for larger bowl turning. Thanks for your suggestions. Happy turning.
     
  2. hockenbery

    hockenbery AAW Advisor Staff Member

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    I jamb chuck the warped bowl over my chuck with the jaws open a bit.
    I leave a center point in the tenon. If you don’t have a center point mark one.

    Line up the high and low points of the rim. This gives you the biggest bowl you can turn from the warped bowl.

    True the outside and true the tenon.

    This is a video of a demo I did where I mount and turn a very warped bowl.

    Mounting and turning a dried bowl -
    View: http://www.youtube.com/watch?v=sCZWsHB4vlM
     
    Last edited: Oct 19, 2017
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  3. Gary Beasley

    Gary Beasley

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    Glenn Lucas has a novel solution for this. He has discs mounted on faceplates with a second layer with a gap through the middle and rubber faced. He mounts up the bowls with the high sides in the gap centering the rim on the disc and seating the tailstock wherever it hits. If the tenon winds up offcenter of the rim then it gets corrected so the bowl has maximum thickness to turn. You need to plan ahead and use as big a tenon as you can use so there is room for correcting.
    After this you can mount the bowl and gently bring it back to round and finish it.
    I intend to build one for myself though I'll probably put a tenon on the disc to save my faceplate.
     
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  4. Lamar Wright

    Lamar Wright

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    Hi AL, thanks very much. This is a tremendous help for me.
    Thanks Gary, I was wondering about the tenon and knew that I needed to use a larger tenon to make room for the correcting. It's not a very large bowl, just 6".
     
  5. Gary Beasley

    Gary Beasley

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    Glenn also showed us a neat trick with the tailstock when doing critical centering. He said because of the point not alway staying centered as it digs into the grain to put a golf ball between the tailstock and bowl and the bowl won't be pulled off center as you tighten it.
     
  6. William Rogers

    William Rogers

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    At the symposium Al Stirit removes the point from the rotating tail center. He said this was better to position the wood as once the point makes an impression it wants to go back into s the same place.
     
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  7. odie

    odie

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    Lamar......unless you intend to mount to a waste block and faceplate, I probably don't have much advice I can offer you......with the exception that initially taking many very small cuts to get your bowl to round. Getting it to round is probably the most intimidating part of the process for someone who hasn't done it before.

    Good luck.....:D

    Keep us posted.....

    -----odie-----
     
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  8. Dennis J Gooding

    Dennis J Gooding

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    I use a method similar to that described by Al Hockenbery, but sometimes with a a couple of twists. Like Al, I remount the bowl over a partly-opened large chuck (usually the one for which the tenon was sized) and bring up the tail center to the center mark left from the original rough turning process and tighten it moderately. If this centers the bowl adequately I am done with this step. If it doesn't, then depending on the nature of the error, I may try tapping the rim of the bowl to shift it on the supporting chuck. If it is clear that the foot of the bowl needs to be re-centered, I insert a small (say 1" x 1") square piece of thin plywood between the foot and the live center and snug up the tail stock. Now, I tap the edge of the bowl foot and/or the rim of the bowl as needed to get the best position. The square of plywood will slide fairly freely over the foot while its opposite side is pinned by the live center. I then tighten the tail stock fully and, optionally, run a bead of CA glue along two opposite sides of the plywood square to hold it permanently. Then I re-turn the bowl tenon.

    At this point, I decide whether the bowl is resting stably against the chuck in the head stock. If I have any doubt, I remount the bowl in the chuck by its new tenon and use a flat scraper to turn a shallow groove on the inside of the bowl just large enough to allow the bowl to be re-mounted on the chuck in an expansion mode and bring up the tail stock for further safety.
     
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  9. Mike Johnson

    Mike Johnson

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    When roughing the bowl I usually use the tail stock center to provide a center point on
    the inside of the bowl and on the tenon, this provides 2 reference points to center from
    after drying. Depending on the depth of the roughed bowl I will also provide a tenon or a
    recess on the inside of the roughed bowl to allow mounting it in either position. This method
    allows me to use the adjustable chuck to secure the roughed bowl and clean up the out of
    round tenon or recess. Depending on how far out of round the bowl is the tail stock center
    can be used to support the roughed bowl while cleaning up the tenon of recess. After the
    first recess or tenon is cleaned up you can reverse mount the roughed bowl and clean up
    the 2nd tenon or recess for mounting into the adjustable chuck to finish turning the bowl.
     
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  10. Lamar Wright

    Lamar Wright

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    Hi Odie, all day today I have been at the lathe trying different methods that I have read about and from videos and advice from the great turners here on this forum. It has been a slow go so far taking small cuts using a large chuck. Tomorrow I am going to try a waste block and maybe my faceplate. I almost have the bowl round and I need to work on the tenon as it has a warp also. This is a learning process for me and I enjoy working on something challenging.
     
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  11. Lamar Wright

    Lamar Wright

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    Hi Mike, this is another good idea. Never thought of making a tenon inside the rough bowl. As thick as my rough bowl is at the bottom I'd have plenty of room for a tenon.
     
  12. Lamar Wright

    Lamar Wright

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    Thanks Dennis, I can see there are several different ways to turn a green bowl. I know that I can take something from these wonderful suggestions and soon be successful.
     
  13. Gary Beasley

    Gary Beasley

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    This is another point Glenn Lucas made in his program. He told us to make the bottom as close to finish thickness as you can and make the sides 10% oversize. This he said reduced the incidence of cracking by a large degree because the bottom did not shrink near as much as the sides. I guess the oversize depends on the wood too, I suspect some varieties distort more than others.
     
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  14. hockenbery

    hockenbery AAW Advisor Staff Member

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    Lamar,
    There are lots of ways to return a bowl. Each have advantages.

    Focus on the techniques to turn it back to round.
    Take small cuts with a sharp gouge.
    Don’t let the gouge bounce on the interupted cut.
    Getting a clean surface with the interupted cut may be one of the more difficult things to do in woodturning.

    You need clean cuts when truing the bowl to round because those cuts are close to the finished surface.
    In the video I take my time truing the outside. I work from smooth into the rough gradually bringing the bowl into round. In theory there is a line on the outside of the bowl that does not have to be cut to bring the bowl into round.

    Turning NE bowls is great practice for the interupted cut.

    He more outdo the better they go.
     
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  15. Gary Beasley

    Gary Beasley

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    image.jpeg
    I broke down and put one together. Hope this makes it clear what I was talking about.
     
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  16. hockenbery

    hockenbery AAW Advisor Staff Member

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    That is a quick way to line up the rims.
    When I jam chuck on an open chuck it takes a minute or so to align the rims.
     
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  17. Lamar Wright

    Lamar Wright

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    That makes since Gary. I left my bowls an 1" thick at the bottom but I was lucky that I have no cracks in my green bowls so far. My green bowls are all maple.
     
  18. Lamar Wright

    Lamar Wright

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    Hi Al, that is exactly what I'm doing is taking small cuts with a sharp gouge. I have the bowl I'm working own almost round. I see that working real slow is your friend when rounding a green bowl. I saw how you made small cuts on the outside of the bowl it in your video.
     
  19. Lamar Wright

    Lamar Wright

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    I see that lining up the rim on an open chuck like I did is a very important step in this process.
     
  20. Lamar Wright

    Lamar Wright

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    It really does Gary, a picture is worth a thousand words as they say. I now see how this jig works. I will be making one of these myself and see how it goes. Thanks a lot Gary.
     

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