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Thread: Piece cracked

  1. As you can see from the prior posts, there are a number of methods to try to prevent cracking. Here's what I do for my twice turned hollow forms. When I harvest green wood, I always seal the ends (Anchorseal) right after it's cut. When it's time to turn, if there is any checking on the ends, I cut them off first; start with a defect free blank. In contrast to others, I usually turn with the pith in the center ( I'll get back to my reasoning at the end). When I turn the rough form, the bottom is turned with a 1.5" diameter (approximately) "drive shaft". The drive shaft runs between the tenon in the chuck, and the bottom of the HF. This eliminates the mass of wood at the base that would otherwise dry slower than the rest of the piece. If it's a tall HF, I use a steady rest for the hollowing process. Once the outside shape is completed, I coat it with Anchorseal, including the drive shaft and exposed area of the mounting tenon. I hollow leaving a 1/2" wall thickness, including the bottom. Once the piece is off the lathe, I coat the tenon area that was in the chuck with Anchorseal. I weight it and record the date and weight on a piece of paper that I leave in the top opening of the HF. I then put it in a paper bag and hang it upside down. I'll leave the paper bag on for about a week, and then let it hang exposed to air, and weight it once a month. Usually takes 3 - 4 months for the weight to stabilize.

    And now for the issue of the pith. My theory is that the rings around the pith are somewhat concentric and they should shrink down in a somewhat uniform fashion. A blank that is taken out of the log to the side of the pith now has rings that are somewhat "C" shaped. When the wood shrinks, it will tend to pull in opposite directions from the open side of the "C", possibly resulting in a crack. As I say, this my theory. As long as I slather all external surfaces with anchorseal, have a uniform wall thickness, and dry slowly, I have been very successful in having crack free rough turned HFs.

  2. #17
    Join Date
    Feb 2008
    Location
    E TN, near Knoxville
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    8,208
    Quote Originally Posted by Edward Weingarden View Post
    ...

    And now for the issue of the pith. My theory is that the rings around the pith are somewhat concentric and they should shrink down in a somewhat uniform fashion. A blank that is taken out of the log to the side of the pith now has rings that are somewhat "C" shaped. When the wood shrinks, it will tend to pull in opposite directions from the open side of the "C", possibly resulting in a crack. As I say, this my theory. As long as I slather all external surfaces with anchorseal, have a uniform wall thickness, and dry slowly, I have been very successful in having crack free rough turned HFs.
    The piece with centered pith will definitely shrink without the lopsided warping you get when off center. But sometimes juvenile wood around the pith will have higher rates of shrinkage than the older rings, depending on the species and how fast the young tree grew. This can leave the sides perfect but star cracks in the center. Anchor sealing all the way around is a great method.

    JKJ

  3. #18
    Join Date
    Feb 2008
    Location
    lufkin tx
    Posts
    2,026
    A few comments on wood problems-- Wood shrinks more across the grain-far less with it. Dense, fine grain woods are strong and pull themselves apart when drying Soft weaker woods are far less likely to split While drying. Wild grain patterns in wood will move and split without great precautions. Species in both catagories vary greatly. We are raised in a culture that is taught uniformism as in wood is wood. Nature never read that book. Try to never be surprised by anything. End seals and time cuts my losses to < 5% of pieces. Piths and roots can be seasoned with little extra effort and endseal. I just finished out a E. Indian rosewood 10" bowl with 1/4 " flared sides with the pith and tight knots radiating running longgrain through the side---lucky too. Pith and the juvenile wood around it are sorta hairy--on hollow forms and vases ect. you can drop CA unto the bottom. Soaks in nicely--try 2 doses also. I use glueblocks and thick CA to mount pieces and leave them until after finishing and have no problems from pith and juvenile wood.
    Last edited by robert baccus; 09-10-2019 at 11:07 PM.

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