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Wood Drying Kiln Temp?

Discussion in 'Woodturning Discussion Forum' started by Tom Hansen, Jun 15, 2020.

  1. Tom Hansen

    Tom Hansen

    Joined:
    Apr 25, 2020
    Messages:
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    Location:
    Portland, OR
    I picked up a broken mini fridge, about 12 cu. ft. and rigged up a single bulb inside. Anyone have the definitive answer on what temperature I need to be aiming for to dry out once turned blanks? Is there such a thing as too hot or too cool? Do I need to worry about mechanically evacuating humidity inside periodically or would opening the door a couple times a day suffice? Maybe I want to keep as much humidity inside as possible to avoid cracking? I'm planning on blanks about 1".

    I have zero experience with drying in anything other than a paper bag. Is there a thickness that's too thick and would cause cracking problems? Too thin?

    Any and all of your experience welcomed.
    Thanks in advance for your help.
     
  2. Karl Loeblein

    Karl Loeblein

    Joined:
    Feb 12, 2018
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    Location:
    Millington, TN
    Start with a full kiln if possible to keep the moisture up so your turnings don't dry to quickly. Suggest keeping the heat around 100 degrees for the first few days and then slowly raise the temp to 120 degrees as the wood starts to dry out. Also, put a couple of small vents in the top that can be closed off if moisture gets too low. Your goal is to keep the moisture level the same throughout the pieces as much as possible.
     
  3. Richard Coers

    Richard Coers

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    Peoria, Illinois
    I start at 90 degrees for several days. I open the door occasionally to release some humidity after experiencing some mold problems with a huge load of red oak bowls. When that happened I washed with diluted household bleach and back to the kiln. Then start slowly going up from there. Speed and heat depends on wood species. Ash and walnut can go pretty fast, fruit woods and white oak, much slower. If the wood had any sign of insects. particularly powder post beetle, I take it to 150 degrees to sterilize the wood.
     
  4. Dean Center

    Dean Center

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    Location:
    Bozeman, MT
    Back when Dale Bonertz was making and selling rough turned bowls and drying them in a homemade kiln, he told me that heat wasn't the key ingredient in the process, it was the air movement. I think he only heated up to 80 or 90, at the most, with a very slow start to the process.
     
    Mark Hepburn likes this.
  5. Kevin Weir

    Kevin Weir

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    May 13, 2020
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    Location:
    Ontario, CA
    Another tool you can use in the drying process is weight. When my drying box has bowls in it, I weigh them once a week, turning the heat up from 90 degrees to about 120 over the course of several weeks. Once the weight stabilizes, additional time in the kiln is of questionable value. A small kitchen scale handles up to 4 kg or about 9 pounds.

    I use an old school method of coating any end grain on wet-turned bowls with paste wax. This helps reduce checking and slows the drying, redirecting the moisture loss to face grained areas.
     
  6. Tom Hansen

    Tom Hansen

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    Location:
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    That was also something I was curious about. I considered anchorseal or even parafin on the end grain. I've lost a lot of wood to cracking so I'm a bit jumpy to say the least. Most was fruit wood but still. Just a light coating of pastewax?
     
  7. Richard Coers

    Richard Coers

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    Peoria, Illinois
    If you are doing a lot of thicker fruit wood rough outs in the kiln to double turn, it helps a lot to stay further away from the pith than most other species. Also put a nice big radius on the top edges of the rim. Sharp edges like to start cracking more easily.
     
  8. Kevin Weir

    Kevin Weir

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    May 13, 2020
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    Location:
    Ontario, CA
    Hi Tom. Paste wax is cheap and mostly paraffin so I usually apply a heavy coat, not only to end grain but also to crotch and figured areas. Some fruit wood, especially apple, has a high ratio of tangential to radial shrinkage. So it tends to be difficult to dry without checking. In this case, slower wins the race. Many of the apple bowls I turned have air dried for more than a year with very gradual kiln drying. If there’s a step to hurry through, it’s rough turning. The more time a fruit log or plank sits after cutting, the greater the risk of checking.
     
  9. John Tisdale

    John Tisdale

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    Dallas, TX
    Dave Bunge likes this.
  10. Tom Hansen

    Tom Hansen

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    Location:
    Portland, OR
    Thanks for the link John. That's a great read.
     
  11. Tim Tucker

    Tim Tucker

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    Penrose, NC
    That is a lot of good info. I add my kudos for you posting that link John. Thank you.
     

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