I copied this from a gift that I received last Christmas.  I don't have a scanner to show you the finished product, so you will have to use your imagination.  The plans below are not to scale.  Use them as a guide to make the form and the rest will follow.  I start with a 25" long piece of wet oak.  After it comes out of the mold and dries for a couple of days, I cut it to final dimensions.  The length along the outside of the curve is 15.5" or so.  The extra length may seem wasteful, but it really makes it easier to shape on the mold.
    The mold was constructed by laminating  pine to get a good 2 inch's thickness.  You can rough it out on a band saw.  Since I don't have a compass plane, I used rasps and files to refine the curve.  I also put some wax on it, just in case.
    The thickest part is about 5/8" at the apex of the arc and tapers down to about 1/16" at each end.  I recommend only tapering the outside of the arc.  A compass plane would really be handy here, but a jack and block plane will get you there.  I found that I could level the surface along the taper, by drawfiling.  See the picture below for the hole angle.  A little scraping after that and Bob is your Uncle.
    To use, insert the neck of bottle into the hole.  Place upright on table and tweak the balance by changing the position of bottle in hole.

    The 5" mark on the mold is the location where the ends are trimmed off. (Both Sides)

    I would be glad to answer any questions you may have about this project.
        Anatol