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Steam bending ideas

Discussion in 'Woodturning Discussion Forum' started by Rich L., Oct 22, 2006.

  1. Rich L.

    Rich L.

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    Oct 5, 2006
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    I'm building a midlands corner chair and would appreciate advice on bending rungs. Any ideas about grain orientation or length of steaming time would be helpful.
     
  2. sjbrandt

    sjbrandt

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    Dillsburg, PA
    The single most important requirement for steam bending is having straight-grained wood with no runout or knots. It helps to have a fresh log to work from. Steaming time isn't as long as you'd think--you can actually dry out the wood too much to bend if you steam it too long. The wood has to be both hot and wet to bend well. When I bend windsor chair parts I typically leave them in the box for about 20-25 minutes under heavy steam. This time-frame works with all the cross sections I've ever needed, from 5/8" (severe bends) all the way to 1 1/2" - 1 3/4" (moderate bends). My experience has been primarily with Red Oak and Black Locust.
     
  3. Mark Mandell

    Mark Mandell

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    Rich,

    My bending experience has been with flatwork, so be forewarned.

    Different woods have very different "bending characteristics." Cherry, for instance, can be bent, but is a CIB to do, whereas ring porous species like Oak, Ash and Mahagony bend beautifully. The normal rule is 1 hour at 212* per inch of thickness. The factories cheat on this 'cause they have high pres/temp steam and hydrolic bending machines.

    Normally dimensional stock is used for bending. If you are bending turned spindles with different diameters and profiling along the way, I would anticipate you're going to run into some special problems, not the least of which will be bending marks and changes of the profiles. Again normally, you'd make a bending jig to match the final curve, heat your stock, and then clamp it in the bending form to cool. The wood takes the curve of the form and all's well.

    Now, I think you've got to make two negative form profiles to match your spindles and their intended final shape, but also curved, so that you can clamp the pieces in the form. THAT's gonna get complicated to say the least.

    Good luck, and post a pic of how you wind up.
     
  4. Rich L.

    Rich L.

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    Oct 5, 2006
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    stam bending

    Thanks for the replys. I'm building the chair using cherry, and anticipate using both a male and female mold to form the spindle shape. Grain orientation and length of steaming are my main concerns.
     
  5. pfduffy

    pfduffy

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    Apr 27, 2004
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    Williamsburg, VA
    steam bending

    The grain needs to be straight and true, but you know that already from your Windsor chair experience. Green wood needs to be about 35% moisture content. A quick way to check this is to fill a pipe with water and stick the work piece in. If it floats, our MC is too low. I don't bend sawn wood, but you know that as well. Just try to make sure all the parts have straight grain, all the forms and pegs and wedges are handy to the forms, get the steam hot as you can, and then relax for an hour while your wood cooks. Work quickly and don't strain a gut muscle when you pull the wood around the form! Good luck. Phil
     
  6. MichaelMouse

    MichaelMouse

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    The obvious but unmentioned is that you're much better with rived wood than sawn. Riving gets things along the grain better than any sawyer's eyeball from ten feet.

    If you don't or can't rive the stock, use the old trick of bandsawing the quarter figure using the annual rings as guide for the first pass, pin for thickness on the second. Works pretty well.

    Not knowing what your ultimate curve will be, difficult to say what method would be best, but I'd look for a three-point jig using the tenons and a midpoint. Note that anything you do in the way of turning will alter the basic best-fit arc, so find out if you'll get kinks and brace them, even unto the full form if you have to, I suppose.
     
  7. windsors

    windsors

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    Cherry will bend well if its green and rived. The problem being the flat spots you will get on your turning after the fact but, if you don't crush the fibers misting it after it dries may bring it back a bit.
     

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