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Thread: Drying a bowl in a convection oven

  1. Drying a bowl in a convection oven

    Hi All,
    Just wondering if anyone has tried this and if so what the results were.
    Thanks,
    Jeff

  2. #2
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    Doing it in a microwave gets the bowl pretty hot. I would think a convection oven would be even worse. The advantage of a microwave is that it works by making the water molecules move. As they do they heat up. I'm guessing that by making the water molecules move it also helps drive them out of the wood. Others may have more experience but I'm thinking that a convection oven would be like a kiln (as long as you didn't get it too hot).

  3. #3
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    If the oven has a setting around 90 degrees it might work. You can't throw a lot of heat at wet wood without making firewood out of it.

  4. #4
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    My opinion:

    1. If you want to dry something really quickly, put it in the oven and pull it out just before it smokes, or put it in a microwave or put it out in the hot summer son. Or alternate between all three. Perhaps you can get it bone dry in a day or less. (Perhaps it is ready for the fireplace at that point).
    2. If you want to keep something from cracking, dry it very slowly. As slow as you can go before it molds. If you leave it in a log form, plan on it taking a decade or more (not advised) - - or if you want to speed it up, rough turn it to shape with uniform 10% wall thickness and wait perhaps 6 months.

    I've had better results with the second option.

    I think that the correct answer depends on the type of wood and how much risk you are willing to take regarding cracks.

  5. #5
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    I was around lumber mill most of my working life. The Pine mills used kilns with high temperatures ~ 180F or higher with a lot of fan speed across the lumber and no dehumidification.

    The hardwood mills varied a lot. They typically dried wood that had been stacked outside for at least two years. The Kiln temp was low (<100F) and the time in the kiln often was up to 6 mo and dehumidification was used. My favorite was a piano manufacturing plant in MS. which was a huge warehouse that was heated to the 80's and humidity controlled. They had guys on electric fork lifts moving stacks of stickered wood around. They had some beautiful wood in that kiln.

    So, to the point - if you are in a hurry and the turning is thin and you don't really care if it cracks, heat her up in a convection oven. If you live in Arizona it will take less time than if you live in New Orleans or Houston. The convection part of the oven helps. The more air flow the better. If the turning is a keeper, then low, slow is the answer.

  6. #6
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    Quote Originally Posted by Jeff Walters View Post
    Hi All,
    Just wondering if anyone has tried this and if so what the results were.
    Thanks,
    Jeff
    What is the wood and the wall thickness (and the base thickness)? Thicker wood of some species may have to be dried slowly to prevent cracking. Some people have good luck with a "kiln" made by putting a light bulb in an old fridge.

    JKJ

  7. #7
    I'm having lots of luck with a Freezer Kiln. Speeds up my drying time exponentially!
    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 . . . . .

  8. The reason I was asking about the oven is because Im going to be turning a series of 15 Maple bowls and they will not fit in my microwave. I will be rough turning them to about 3/4. I sold 3 of the same size bowls on Saturday so my hope is that I could have them ready for my next show the first weekend of December if possible.

  9. #9
    Too bad you don't live near me. I'm sure we could dry them in my freezer kiln in less than a month. Might be worth your time to try to find an old freezer and make one?
    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 . . . . .

  10. Sorry to ask a silly question but I need to ask. What metal is the bowl made of?

  11. #11
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    This is an older thread, but let me ask a different, but related question:

    Has anyone tried vacuum drying? I read on-line about all of the benefits of vacuum drying. It was first patented around 1905. Perhaps this could be the ultimate in minimum cracking. Of course, the downside is you'd need to run the vacuum pump for some period of time. I know that commercially there are people doing vacuum drying of high value wood (sometimes in conjunction with other things like microwaving, etc.). But I'm wondering if any SMC people have ever tried it and if so, how long did you need to run the vacuum?.

  12. #12
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    About a year ago Dave Hout and Ernie Conover published a Youtube video where they use dessicant beads for drying turned bowls, how to use it and how it works to draw the moisture from woodturning blanks. They claim that the dessicant let you dry out green, wet wood up to 1'' thick in just 12 to 48 hours, with little to no checking or cracking. Surprisingly, it doesn't seem to have gathered much interest.

  13. #13
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    Quote Originally Posted by Brice Rogers View Post
    This is an older thread, but let me ask a different, but related question:

    Has anyone tried vacuum drying? I read on-line about all of the benefits of vacuum drying. It was first patented around 1905. Perhaps this could be the ultimate in minimum cracking. Of course, the downside is you'd need to run the vacuum pump for some period of time. I know that commercially there are people doing vacuum drying of high value wood (sometimes in conjunction with other things like microwaving, etc.). But I'm wondering if any SMC people have ever tried it and if so, how long did you need to run the vacuum?.
    Vacuum kilns work well because under a hard vacuum you can get water to boil around 90 degrees F. You get very little degrade with a vacuum kiln. The issue is keeping the inside of the kiln 90 degrees since heat does not radiate in a vacuum. Some kilns used aluminum plates between the layers of wood. These plates have water tubes sandwiched between 2 aluminum plates to allow warm water to be circulated from outside the kiln. Woodmizer used an industrial looking electric blanket with limited success. At the most simple form of vacuum kiln drying, you put the wood in a vacuum bag and draw a vacuum. Occasionally you open the bag and let the wood warm up in a warm box. Or you can put it in a tub of warm water. But it takes a lot of labor to babysit the process.

  14. #14
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    Heat radiation in a vacuum

    Quote Originally Posted by Richard Coers View Post
    ...The issue is keeping the inside of the kiln 90 degrees since heat does not radiate in a vacuum....
    I suspect you meant to say there is no heat convection in a vacuum. Heat radiates well in a vacuum, otherwise the sun would be useless to us for warmth. Radiation is also the means to remove excess heat from things such as satellites and planets.

    The difficulty without convection or radiant heaters would be to heat the wood on all sides equally to minimize the heat gradient within the wood, the reason for the heat exchanger you described.

    JKJ

  15. #15
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    Maybe I'm a bit still in the old school, but I still use DNA for soaking and drying green turned bowls. I've tried several other methods but I was losing way too many blanks. Learned about the DNA method and I lost zero bowl blanks. I was sold on the process from then on. I haven't tried a "freezer kiln" yet, but I guess I need to give it a try sometime.
    Thanks & Happy Wood Chips,
    Dennis -
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