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Thread: Help drying hollow forms

  1. #1
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    Help drying hollow forms

    I recently obtained the D-way hollowed which allows for 6-8 inch hollow forms and did a couple practice forms but am unsure how best to dry. Prior to this I’ve only turned bowls from green wood and I finish turn in one try.

    After turning a couple of maple forms to an equal wall thickness (about 1/2”), I put them in a paper bag with shavings but noticed that they started to mold after a couple days. I took the shavings out and put just the vases in the paper bag and for the last 4 weeks they’ve been okay and are almost dry without cracking.
    Tonight I turned one out of cherry but in my single prior experience with cherry, it cracked in numerous spots so I’m nervous that this one won’t last. My end goal is an urn, so I will need to fish turn it.
    Any tips? Should I put it in a paper bag with shavings off the ground and let it sit or do you move them every couple days? Any advice would be appreciated.

    thanks,
    Tom

  2. #2
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    From what I've read, Cherry is likely to crack.

    I think that on a hollow form, it is a good idea to wrap the outside with stretch wrap but leave the center open.

    Wet wood is swollen. So if the outside dries (that is - - shrinks) first the outside will crack. If the difference between the inside moisture content and the outside is kept close to each other the stresses will be reduced. You want the whole thing to slowly lose moisture. So, I think that if you wrap the outside with stretch wrap and let it dry from the inside, it will dry/shrink more slowly and the inside will shrink first.

    When you're turning and stop for lunch or for the evening, it is best to wrap a plastic bag around the piece to retain the moisture.

  3. #3
    Hey Tom, being in Milwaukee I have the same climate as you. I've also found that using too many shavings in the paper bag will let mold grow, a handful or two is all I use now. Our relatively high humidity seems to do a good job of letting the wood dry slowly.

  4. #4
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    Some ways people have used successfully on things turned green. Note that success in any method assumes there is no pith in the turning and better, no juvenile wood (wood near the pith).

    - Paper bag, no shavings.

    - Double paper bag, no shavings

    - Pile of loose shavings, no bag.

    - Plastic bag, once a day remove and invert the bag, dry side in. Don't skip a day.

    - Put in a refrigerator/freezer kiln with light bulb, some vent holes. The warmth helps dry quicker and the high humidity inside prevents most cracking.

    - Anchor seal the end grain only on the outside, doesn't apply for hollow forms turned in end-grain orientation.

    - Anchor seal the outside only, 100%. Slows drying from the outside, lets it dry more from the inside out. This is my preferred method when I turn green wood.

    Note that cherry is cherry except for stability. I have had some cherry start cracking while I watched after cutting down the tree. Some solid blanks crack and split clean through. On the other hand I have had cherry that was about as stable as mesquite. Wood from one particular tree simply refused to crack, even on the end grain of a round section I left outside in the sun for years. Thick blanks I cut from that tree and put up to dry indoors never even checked. Go figure.

    Most cherry is somewhere in the middle. I have dried many dozens of solid cherry blocks without cracking, from 2x2 to 6x6 and larger. I Anchorseal the end grain, any wild grain, and sometimes all over. Some have been drying for over 10 years, indoors on wire shelving, in heat and air conditioning. I might lose one blank out of 100 if I'm unlucky. (These days I almost always turn dry wood only.)

    JKJ

    Quote Originally Posted by Thomas Wilson80 View Post
    I recently obtained the D-way hollowed which allows for 6-8 inch hollow forms and did a couple practice forms but am unsure how best to dry. Prior to this I’ve only turned bowls from green wood and I finish turn in one try.

    After turning a couple of maple forms to an equal wall thickness (about 1/2”), I put them in a paper bag with shavings but noticed that they started to mold after a couple days. I took the shavings out and put just the vases in the paper bag and for the last 4 weeks they’ve been okay and are almost dry without cracking.
    Tonight I turned one out of cherry but in my single prior experience with cherry, it cracked in numerous spots so I’m nervous that this one won’t last. My end goal is an urn, so I will need to fish turn it.
    Any tips? Should I put it in a paper bag with shavings off the ground and let it sit or do you move them every couple days? Any advice would be appreciated.

    thanks,
    Tom

  5. #5
    A couple of months ago I tried soaking a couple of cherry bowls
    in DNA (De-natured Alcohol) for a couple of days in a sealed container.
    The results so far have been less warpage, no cracking, significantly less drying time, and both bowls have maintained a brighter cherry color. You might want to consider this option for your cherry hollow form. Just be prepared to stick it in a paper bag or box to slow down the initial drying.

  6. #6
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    Oct 2015
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    Tuscaloosa, Alabama
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    I often use the D-Way system for hollowing small vessels. Almost all have been green turned "pith to pith" to final thickness of 1/8-1/4 inch depending on the wood. On most, I sand the outside using BLO as a lubricant and to create a pore filling slurry, I then drip thin super glue inside to seal the pith, allow glue to dry for a few of minutes, coat the interior with shellac, wrap the outside with stretch wrap. So far so good with minimal cracking. I have been able to easily repair the few small cracks with CA glue or epoxy. As an aside, I have re- ground one of the D-Way carbide bits to a narrower cutting tip for quicker hollowing then follow with the standard bit and finally a standard bit with a negative rake to help smooth the interior. Hope this helps.

  7. #7
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    I forgot to mention that boiling the rough-turned piece is a proven way to improve drying success. There was some info and discussion of this recently and less recently.

    Something the other John Jordan does after turning a hollow form from green wood is put an air hose nozzle in the open end and blow compressed air inside, sealing the opening with his hand. I haven't done any comparison tests of using/not using this method but it sure does bubble out a bunch of the free water in the wood.

    JKJ

  8. #8
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    Thanks everyone for the suggestions. This was a smaller diameter piece (started at 7 inches with bark, now at about 5 1/2 inches) so still has the pith. I’ve sealed the end grain and will dry slowly. I’ll take a photo later tonight and will let you know how it goes.
    tom

  9. #9
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    Quote Originally Posted by Thomas Wilson80 View Post
    Thanks everyone for the suggestions. This was a smaller diameter piece (started at 7 inches with bark, now at about 5 1/2 inches) so still has the pith. I’ve sealed the end grain and will dry slowly. I’ll take a photo later tonight and will let you know how it goes.
    tom
    Way to thick of wall for a hollow form with the pith in it. You should be down to around 1/4" max. 1/8" is even better. Even there, some would drill out the pitch with a 1/4" bit and then plug it when dry.

  10. #10
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    Quote Originally Posted by Richard Coers View Post
    Way to thick of wall for a hollow form with the pith in it. You should be down to around 1/4" max. 1/8" is even better. Even there, some would drill out the pitch with a 1/4" bit and then plug it when dry.
    Yeah, I thought I needed to leave it thicker so I could true it up. Live and learn I guess.
    thanks for the help.
    tom

  11. #11
    If you are going to twice turn a pith to pith you can leave the walls 1/2 to 3/4 thick. Leave 3 inches of material at the base and make a part at the bottom of the hollow form stopping around 3/4 inch. At that point your part should be in the pith. Anchor seal the outside of everything and let it dry. The hunk of wood you left on the base might crack but the crack shouldn't transfer to the turning. The small chance it does It will not be bad and can be turned out.

  12. #12
    I like to turn hollow forms as often as I can. I now leave a small tenon to grab with my chuck to sand when dry. I do use a freezer kiln and often wrap the outside with stretch plastic to try to slow the outside. I do get some checking and cracks but am lucky enough to have lots of wood so loosing one or two doesn't bother me too much.
    Quote Originally Posted by Thomas Wilson80 View Post
    Yeah, I thought I needed to leave it thicker so I could true it up. Live and learn I guess.
    thanks for the help.
    tom
    Pete


    * It's better to be a lion for a day than a sheep for life - Sister Elizabeth Kenny *
    I think this equates nicely to wood turning as well . . . . .

  13. #13
    Maple likes to mold, and I would guess that one reason for that is it has a fair amount of sugar in it. I don't put the stretch film on it because it always molds under the film. Lately I have been drying my bowl blanks without the stretch film on the rim. Over the years, I have noticed, especially with the Pacific Madrone, which likes to start splitting before you even get the chain saw out, that I get far less cracking with spring harvested trees than I do with mid to late summer trees. Having that spring sap in the wood seems to do a lot for crack prevention. If you dry with shavings, the shavings need to be dry. Christian Burshard, who has done every thing conceivable, and a lot of things inconceivable with madrone, dries his pieces in a paper bag which is inside of a plastic bag. The paper bag gets changed out every day.

    robo hippy

  14. #14
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    I turn hollow forms to 10% thickness or slightly less depending on the size of the form. I use the Denatured Alcohol method (not advocating, just something that works for me). I soak the rough-out in DNA for at least 24 hours (longer soak times doesn’t hurt a thing) and then wrap the outside of the form with a brown paper bag. Make sure the outside is covered with the paper but leave an opening to the hollow form so air can circulate within. The idea of the paper is to slow down the drying of the exterior surface compared to the interior.

    I usually wait for a couple of months before finish turning because I am in no rush but have finished turned forms in 4 weeks.
    Steve

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  15. #15
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    Thanks again everyone for all the info/advice. I pulled it out of the shavings today to check and so far no cracks, but we’ll see what happens.
    Attached Images Attached Images
    Last edited by Thomas Wilson80; 06-30-2019 at 10:35 PM.

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