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Once turned green bowls?

Discussion in 'Woodturning Discussion Forum' started by Ron Vasser, Jan 26, 2020.

  1. Ron Vasser

    Ron Vasser

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    I've turned 2 NE walnut bowls one at ¼" and one a little less. I turned both with continuous curves no straight walls and they are 15 inches on the long side. I'm in N GA and the weather is cool and humid. I left one bowl out on a shelf and bagged the second. Both bowls cracked after a couple of days. I know you have to pay your dues while learning the process but I sure need some advice on this problem. You all know the quote " to continue to do the same thing and expect different results is insanity" or something close to that. I tried some Danish oil on a smaller bowl to try to stop the cracking and after a few days I tried to sand but it just gummed the sandpaper. I've prepared 3 more blanks and have them in plastic bags until I get each one turned. I'm open to and appreciate any suggestions.
     
  2. Scott Lynn

    Scott Lynn

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    Might coat it in shallac to slow the drying down so it wont crack pretty sure I read that some were not positive
     
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  3. Mike Johnson

    Mike Johnson

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    The rim of the bowl is the critical part of the green turned bowl that is most likely to check and start the beginning of a crack. The rim of the bowl encounters a large amount of stress during the drying period and usually ends up and inch or two out of round on larger bowls. A good coat of wood sealer on the rim can slow the rapid loss of moisture from this area which can provide more time for the wood to dry evenly. Rounding the rim edge of the green turned bowl can also reduce the "sharp" edges that can start a crack.
     
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  4. robo hippy

    robo hippy

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    I turn all of my bowls that way, and the more they warp, the more I like them. I have had almost no cracking problems with walnut, though I don't turn it any more because it makes me sneezy and itchy. It is generally very stable. For protecting the rim, I make sure to round over the rims, both outside and inside. One reason is that a sharp edge will slice you to the bone if you brush up against it. The other is the sharp edge will start to crack more easily than a rounded over edge, which as near as I can tell is kind of like trying to keep an even wall thickness to reduce/prevent uneven drying stresses. If more protection is needed, I stretch some plastic stretch film over the rim, most of it on the outside, and a little over the inside, maybe 2/3 to 1/3. I do keep them on the shop floor for a few days, then up on a wire rack to finish drying. They are pretty much dry as they will get in a week to 10 days. I don't use the stretch film on maple. I think it is because of the high sugar content, but it likes to mold under the plastic.

    robo hippy
     
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  5. Ron Vasser

    Ron Vasser

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    Thanks, guys, but the rims and the sapwood dried fine. The bowl is 15 inches and thin enough that I see light through the sapwood. The problem is on the sides and close to the bottom of the bowl. I was planning on vacuum chucking, sanding, and removing the foot. It is completely dry now and I'm going to fill the cracks with milliput and finish the bowl as I would if it had not cracked but would like to know what I'm doing wrong. Some photos for a better description.

    -c.jpg -d.jpg -a.jpg -b.jpg
     
  6. charlie knighton

    charlie knighton

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    Try putting in drawer for 4 or 5 days....there is no air flow in the drawer.
     
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  7. Fadi Zeidan

    Fadi Zeidan

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    Looks like it is bottom heavy and cracked where the transition from thinner walls to thicker base.
     
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  8. Ron Vasser

    Ron Vasser

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    The only place on the bowl more than ¼" is the foot around the recess. If that's the problem I'll have to rethink the way I mount the blank.
     
  9. JeffSmith

    JeffSmith

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    Where'd the wood come from? Was it blow down or storm? Cracking along the annular rings is often symptomatic of wind shake. If that's the cause, there's little that can be done except to avoid turning areas that were stressed by repeated bending to very heavy winds. Trees left standing can recover by internal healing and, like a broken bone that heals, is often stronger than the surrounding wood. Those that fall often separate along the growth rings this way.

    I'd try an colored epoxy fill, sand, finish and call it a lesson in discovering the wood's history.
     
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  10. Daniel Warren

    Daniel Warren

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    Seems there’s a knot or inclusion where those cracks are? Also a possibility of ring shake closer to rim?

    in my limited experience walnut has been of the better behaving woods I’ve worked with. The only time I’ve experience cracks was with some portion of the pith remaining.
     
    Last edited: Jan 26, 2020
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  11. Richard Coers

    Richard Coers

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    Drying cracks go perpendicular to the grain, not with it. Those cracks were there before you started turning. You just didn't see them.
     
    Last edited: Jan 26, 2020
  12. hockenbery

    hockenbery AAW Advisor Staff Member

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    My suspect factor is the thick ring at the bottom.
    That thick ring counts as thick wall thickness it doesn’t dry and it doesn’t let the wood move so it cracks.

    You will have more success turning to finish with no foot or a small foot

    Those cracks may have been pre- existing.
    However walnut in addition to being prone to wind shakes is also a wood that splits along the growth rings.
    I have turned lots of hollow balls from walnut by splitting a solid ball along a growth ring, hollowing both parts, gluing on the growth ring, And finish turning the ball. Nearly invisible glue joint.

    I will add a bit more later.
     
    Last edited: Jan 26, 2020
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  13. Dean Center

    Dean Center

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    Ron, it appears to me that the cracks formed in specific places. One crack looks partially like ring shake and in my experience walnut is prone to that issue. The other cracks relate to old branch remnants, which perhaps are acting like separated piths, with high stress or asymmetric shrinkage, compared to the clean grain. I have a heartwrenching number of great big rough turned ash bowl blanks that have cracked at the knots in the wood despite my best efforts to prevent it, to the point where I'm just not turning big bowls from anything but clear wood anymore.

    As noted, you can't really do anything with ring shake.

    I haven't had great luck with turning green to finished, so I'm not the best one to offer solutions. However, a friend who turns has very good luck by putting a coat of finish on the bowl as soon as it comes off the lathe. His preferred finish is Wipe On Poly. Not sure if he also puts it in a paper sack or not, but that's another strategy to slow the drying.

    It's tragic, as that's a really nice bowl.
     
  14. Clifton C

    Clifton C

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    I was going to say the same...
     
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  15. hockenbery

    hockenbery AAW Advisor Staff Member

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    Ron,
    When I take a large NE bowl off the lathe it is finish turned with walls 3/16” thick.
    i wash it in the sink, towel dry it, put it in a cardboard box with the flaps closed.
    After one day I partly open the box leaving one long flap closed.
    After 2 days open all the flaps
    On the third day set the bowl on a shelf then anytime after the 4th day sand and finish the bowl.

    the washing and the box slow the endgrain from drying too quickly.

    also am a big believer in using tenons on NE bowls. The recess leaves a lot of wood to be turned away to get a shape that will dry successfully.

    if I were taking taking more than 15 minutes to hollow the bowl I would mist the end grain with a plant mister every 5 minutes to keep it from drying on the lathe.

    I almost never have a NE Bowl crack following this procedure.


    try a smaller bowl. 10” long 6-8” wide.
    Use a tenon and turn it footless.
    Use calipers to ensure the bottom is an even wall thickness.

    you can see how I do this on a crotch bowl. All the turning is the same for any NE bowl.
    https://www.aawforum.org/community/index.php?threads/naural-edge-bowl-from-a-crotch.11058/
     
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  16. Roger Wiegand

    Roger Wiegand

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    I've been getting much more fussy about not bothering with blanks with defects, and my success in drying without cracks has gone up significantly. I'm with the group that thinks those cracks were present int he blank and just opened up on drying. I don't think any amount of care would have prevented them from opening up.
     
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  17. Don Wattenhofer

    Don Wattenhofer

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    Yup I got into this a bit late, but as soon as I looked at the pictures I thought ring shake and then saw that others had already pointed that out.
    There was one comment about the base being a possible problem but none of the problems were very close to the base plus the fact that almost all of the wood grain in the base area is parallel with the base making it less likely to crack. I have done numerous bowls with the same style base and not had any cracks in the base area as long as the thickness from the center inside to the outside center of the recess was roughly the same as the walls.
     
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  18. Rob Price

    Rob Price

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    The only thing I’ll add is that with NE bowls I try to sand it as soon as the wood will let me and get a coat of oil on it to help slow down drying then off in a paper bag. I’m in Georgia- in the summer time I don’t usually bag them. It’s plenty humid.

    I agree with others- this looks like ring shake and was probably already there or inevitable. The cracking I’ve had from drying has been perpendicular to the grain. Even when they do crack I add epoxy and bow ties. People love that imperfect stuff right now.
     
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  19. Gary Beasley

    Gary Beasley

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    Ive had some limited success when I notice a crack like that with soaking some thin CA into the crack before it goes in the bag to dry. No guarantees but worth a try.
     
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  20. robo hippy

    robo hippy

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    Well, now you know what to look for when it comes to ring shake. That type of cracking is also very risky for turning as the bowl can fail along that crack line and come off the lathe. The plastic wrap won't work on a natural edge bowl...

    robo hippy
     
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  21. Karl Loeblein

    Karl Loeblein

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    Was this wood trunk wood or limb wood? Limb wood has a tendency to twist/cup more than straight trunk wood.

    Seeing the stains I'm guessing this tree had some prior damage. As other have shared, both black walnut and cherry seem to have more ring shake issues than other woods.

    -Karl
     
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  22. Leo Van Der Loo

    Leo Van Der Loo

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    The staining should’ve told you that there was a pre-existing condition in the log that had separation of the year rings.

    A close-up examination of logs and blanks is really mandatory if you want to stay out of trouble and also to know what the outcome of the turning is going to be.

    Start with blacks that have no defects is the way to go IMO.

    The recess has gotten nothing to do with the splitting in this case, though I have had split occur by leaving a thicker tenon on a turned bowl, I changed to using a recess as my standard way of mounting my blanks ever since.
     
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  23. Ron Vasser

    Ron Vasser

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    Thank you all for your help!! The walnut wood I have was cut down about a month ago. I got 38 feet of the trunk wood that was 22 inches to 16 inches in diameter. I was unfamiliar with shakes in trees as I am a beginner woodturner. When I cut this blank I saw no evidence of cracks or the staining that showed after I started turning the bowl and after I saw the staining I was still not aware it was a defect even if it should have told there was a pre-existing condition. I've done some research on timber the past couple of days and went out and cut and inspected some more of the wood. It has ring shakes and heart shakes so a lot of this wood will end up in the fire ring.
    Again I appreciate your time to help me understand what I'm dealing with and for any other folks dealing with a similar problem, I was surprised to find the defects aren't caused by external pressures and temps. This is one of the quotes about shakes.

    "Shakes are natural occurring defects in standing trees caused by a lengthwise separation of latewood fibers. Shakes were once thought to be caused by external stress factors such as wind and temperature extremes (often called wind shakes); however, research has found that a bacterium is the true cause of shake. The bacteria that causes shake enter the trees through the roots and not through the stem. The bacterium belongs to the clostridium genus and is often accompanied by an unpleasant odor."
     
  24. Dean Center

    Dean Center

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    Very interesting quote, Ron. Where did you come across it?

    In wood with ring shake, you can often part the wood up as spindle blanks, though they might be of small cross section. Since it will take 2-3 years for the blanks to dry, you'll have a good start on various non-bowl items you can make in the future.
     
  25. Ron Vasser

    Ron Vasser

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    This guy has some articles on it and I'll have to look up the other place that discussed it. I looked through lots of forestry books.
    Dr. Gene Wengert, forum technical advisor; http://www.woodweb.com/knowledge_base/Causes_of_Shake.html


    I started some spindle blanks already and sealing the ends with candle wax. When I first started I made another big mistake and cut up a huge red oak that never quit cracking. I have lots of it cut into spindle blanks also.
     

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