Green spindle crack prevention

Discussion in 'Tutorials and Tips' started by Mark Levitski, Mar 20, 2012.

  1. I posted this on another turning forum, but please would like to hear what anyone here has to say:
    I have struggled with my goal to produce lamps, weed pots, and vases to hold a glass insert from green wood. You know what comes up as the obstacle--excess cracking. I take a small green log or branch and turn it rough with either a lamp auger for that or a 3/8 hole for the weed pots or a larger hole slightly smaller than my glass insert. I've tried paper bags, which work well for all of my bowl/hf stuff. But the bulk of the wood left in these other pieces is too much to survive the drying process w/o excessive cracking. Sure, I can get away with some inlay for cracks, but I turn to sell and that trick would not work after a certain number of pieces to produce. I have recently constructed a DNA submersion bath as an experiment, yet to be proven for this application. I would really like to find a way through this because I can make some beautiful pieces with burls and leaving the bark on (NE spindle work) to just jettison the idea. Any of you braintrust woodturners have suggestions (don't bother w/ the microwaving thing--too cumbersome for my production)?

    Thanks............Mark
     
  2. Jake Gevorgian

    Jake Gevorgian

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    Hi Mark, I'm not an expert in drying wood in a way so that it won't crack. But, there is a way I've seen before and I think it might help with your situation.
    The method is to wrap up the wood with aluminum foil (except the ends) and put that end (the end only) in the kiln at about 140 F for about two days. Then, chuck it back on the lathe and true it up.
    Now, the tricky part is making the kiln. What I'd imagine would be a box with large diameter holes on the top (a hole that would accept the size of the spindle ends) and inside the box you'd put some high watt lamps to generate heat (if I remember it right, wattage on light bulbs indicates the amount of heat, but I'm too stupid about electricity as you can tell.)
     
  3. John Jordan

    John Jordan

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    Its difficult to dry limbs with the pith in them. Turn the same thing from straight grained wood free from the pith, and put them in your bags, or slow the drying in some way, and you can make all those things from green wood.

    You may promote even drying in the limbs, and not suffer cracks from uneven moisture content, but the overall shrinkage differential in the radial/tangential shrinkage will usually result in radial cracks. A few woods have little enough movement to allow the pith to be included, but not many. Drilling a hole all the way through the center would be somewhat helpful.

    John
     
  4. MichaelMouse

    MichaelMouse

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    If you leave it in the large, curing without cracking is simply a matter of luck and fortuitously random grain. I think I posted this here for another thread, but it's as good an illustration of stress relief by radial check as I have.
    http://i35.photobucket.com/albums/d160/GoodOnesGone/Radial-Checks.jpg

    It was snugged up tight in the chuck to serve as a demonstration that the checks develop from contraction. Only answer we have is to take away enough wood, or precisely the right wood so it can't contact and pull apart.

    If you turn with the heart out, differential shrinkage will still distort the hole you bored, so bore about 10 percent oversize to accommodate that reality. Do not put the test tube in the hole in green wood. At best it's there forever, at worst, it's broken glass. DAMHIKT

    Almost forgot. http://www.hypersurf.com/~charlie2/Turning/WoodShrinkage/WoodShrinakge0.html#Anchor-14210 reading material.
     
    Last edited: Mar 21, 2012
  5. Thanks MM and JJ. John, I will have a look at your wood properties DVD, thank you. I usually claim to be self taught, but especially in today's world w/ the media and internet I can say I was tutored by many.

    I will try all the suggestions, but straight grained wood might be out of the question. What has been selling (and what I prefer) are these type things:
     

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  6. john lucas

    john lucas

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    I completely hollow lamps that are turned from green wood so there isn't any pith or for that matter much of any wood left. I try to use straight sections of trunk and then center the pith to reduce the warping. When I've tried it with limb sections the tension in the wood always makes it warp on one side more than another.
    I had the same problems you are having when turning weed pots many years ago. I never really solved the problem other than just letting them crack and telling the customers that is what wood does. I did dry one using the plastic bag method.
     
  7. John L. Yeh, I have been letting the smaller cracks just go with the piece for the most part. I might just have to accept a certain % loss for these. I have enjoyed and learned some things from your videos--thanks.

    And, Jake (I forgot to include you last post). That sounds like an interesting process. I might have to think about it for a while :)!
     
  8. john lucas

    john lucas

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    Mark If you truely want to change how they look, wait until they crack and then fill the crack with Inlace or epoxy and return it. I have done it on occasion for other projects other than weed pots. It's time consuming so it needs to either be a gift or something you can charge more money for.
     
  9. Jake Gevorgian

    Jake Gevorgian

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    Mark these are beautiful. I personally like them the way they look, even with the crack. It's natural and, today I feel artsy (don't ask me to turn spindles per specs lol.)
     
  10. Steve Worcester

    Steve Worcester Admin Emeritus

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    early on, I had similar problems with my oil lamps, then I got to the pint where I had more than enough dry wood to turn them all from dry wood. There is little distortion and the holes don't smash the glass inserts.

    If it has to be from wet wood, then you should rough them out and hope for the best or maybe even try soap or alcohol or boiling methods.
     
  11. MichaelMouse

    MichaelMouse

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    Burls are almost a license to steal. I keep cherry bark flakes on hand to stuff into any glue-basted cracks that develop. Usually there are one or two other areas of bark, so it goes unnoticed. If you keep your turning within the burl section you'll have less problems with splits. it's the straight wood that does that.

    Then there is another form of cheating involving parting a plug, hollowing through the bottom and sneaking it back with the concealment of a bead or groove. Not that I would ever do such a thing. I'm told that makes it cure like a thin "hollow form."
     

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