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Thread: Question on drying hollow forms

  1. #1

    Question on drying hollow forms

    So I had turned my first hollow form the other day out of carob with the end grain running parrellel to the ways. It was about a 1/4 inch thick through out. I left the tenon on and threw it in a paper bag for a couple of days then left it out in the open air to finish drying after that.

    I checked yesterday and where the tenon meets the bottom of the piece I got some major cracking.

    I know that where the different thicknesses meet is where cracks are most likely to form so my question is this. Are you all leaving tenons on when drying? Did I just not leave it in the bag long enough? I have only seen one video on hollow of form so I have very little info. I like to sand on the lathe when ever possible which is why I left the tenon on. Plus I have worked with Carob a couple of times and it seems to be a fairly stable wood as far as cracks and warping.

    Please school me in your hollow form drying methods.
    Mike Vickery

  2. #2
    Join Date
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    Hey Mike. I think you went too thin with the roughing.

    I'm not the most experienced HF'er around, but I've had good luck with the following protocols.
    • If sopping wet green rough it to a 3/4" thickness and do the dna dance.
    • If only moderately green, I rough and finish turn in one session. And this is especially important when the form get's to 3/8" wall thickness or less.
    Only the Blue Roads

  3. #3
    I haven't turned Carob so I'm not familiar with its characteristics. There are so many drying methods out there its hard to choose some time. I'm not sure any of them are 100% bullet-proof on all woods.

    That said, I have had good luck with the boiling method on several types of woods. I have not tried it on fruitwoods (the most prone to crack in my experience) but I have had success on some "mystery Peruvian wood" I got from Jim King. It wanted to crack even while I was roughing it.

    The method was simple, just rough it out to about 3/4" thick, stick it in a pot that you don't ever expect to use for cooking again and let it boil at full tilt for one to two hours (depending on size and weight). Make sure it doesn't float or sit directly on the bottom while boiling (I used a couple of small sifts). Then put it in a paper bag for at least 4 or 5 days. It will be ugly when you take it out of the pot but that charred surface will turn right off.

    Jim describes his variation of the process on his website. He goes thru a few more steps than described above but this worked fine for me.

    It's always seemed counter-intuitive that to dry a piece of wood you should put it in a pot of boiling water. But it works.

  4. #4
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    Mike. I just turn them to completion right from green. All woods are different but I find if you get them to final thickness of say under 3/8" movement is minimal due to less stress. I've always had problems trying to twice turn them. I'm not saying this is right for everyone but works for me. Here's a couple pictures of some green to finish hollow forms that i did and they still look the same after the passing of time. Alright Andy. Pull out your magic wand and fix my links! LOL!!!




    Last edited by Andy Hoyt; 01-16-2007 at 12:21 PM. Reason: All in the wrist, Kurt :)

  5. #5
    End grain dries at ten times or better the rate of long grain. Quarter dries slower than face, too, because of the structure of wood, by the way. The tenon gets you in trouble because you're sequestering moisture inside and letting the outside contract with no place to go. I like to dish in on the bottoms, making them relatively thin, then stand things up on stickers to promote drying on both ends of the endgrain. the dishing allows the broader exterior a place where it can contract against air rather than uncompressed saturated wood.

    Little bit of creativity in determining your final hold can leave a ridge suitable for grasping and lightly turning out the quarter/face differential on the outside. Who cares about the inside. Let it be an eighth thicker on the quarter as long as people can't get their digital calipers inside.

  6. #6
    Thanks for the advice everyone. Still interested in other opinions.
    Mike Vickery

  7. #7
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    I don't do a lot of hf turning, but if it is green, and I am leaving a tenon on for sanding later, then I put some finish oil in the inside, and some on the bottom of the tenon. This helps slow the drying from this thicker part, and results are usually good. I do turn to final thickness from the start. Also, because I turn them end grain, I can usually sand them because there is less tearout than when turning bowls. I put some finish on and let the hf dry before applying more finish.
    robo hippy

  8. #8
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    For the few I've done, I found the face grain hollow form to benefit from rough turning, drying, then returning. The peice of cherry I did that way warped noticably after drying and IMHO would have ruined the peice.

    For end grain I go from green to finished without noticable distortion.

    Bob

  9. #9
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    I turn mine to 3/4" or so, then DNA it and wrap it in brown paper sack to dry for 2 or 3 weeks. Never lost one yet.
    Bernie

    Never put off until tomorrow what you can do the day after tomorrow.

    To succeed in life, you need three things: a wishbone, a backbone and a funnybone.



  10. #10
    I do a little of all of these things mentioned above...mainly because I learn from everyone here. I really enjoy going from start to finish, but I know that's not always possible...or responsible.

    The only thing I can stress is make doubly sure that there isn't even a smidgeon of the slightest bit of a possible crack in that tenon.... because no matter how you wrap it...it's gonna open up over night and take the whole bottom of your piece with it.
    ~john
    "There's nothing wrong with Quiet" ` Jeremiah Johnson

    I live in Steve Schlumpf's basement...under the stairs

  11. #11
    depending on the wood species, I usually rough mine out to 1/2" or so DNA soak 24 hrs then wrap with brown paper bag, cut a hole out for the opening let it dry upside down. don't think I have ever lost a tenon due to cracks with this method.
    Have Chainsaw- Will Travel

  12. #12
    I do the same as Jim on any green HF, endgrain or facegrain orientation, rough to just under 1/2" or so and use the DNA soak.

  13. #13
    Thanks guys for some reason I had it in my head that you turned them to final thickness before drying.
    Mike Vickery

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