As stated, I like to bore one piece branch flutes while the wood is still green. It's easier on the tools, as the wet wood keeps them cooler, preserving their cutting edge longer. It also speeds up the drying process and greatly reduces surface checking of the wood. By boring out the dense, inner heartwood, the stress between it and the less dense sapwood, as each dries at a different rate, is gone, preventing the checking caused by that stress. I also like to leave the bark on while the branch is drying, which slows down evaporation through the outer surface. Thus, with moisture leaving the wood from inside the bore, as that inner surface shrinks, it will pull itself together around the empty space, rather than the outer wood being pulled apart as it shrinks before the heartwood, the typical cause of surface checking.
But boring out the air and sound chambers is as much as I'll work a branch while green. If not dried before voicing the flute, at least to equilibriuim moisture content, then the nest,
flue, cutting edge and block
may
warp or even split as the branch dries and shrinks, ruining
the tone. The dimensions of the sound chamber may change,
affecting
the tuning. Another benefit to drying the wood is that
whatever finish you use
will adhere better. Also, if you make a branch flute
by splitting, your glue will hold better to dry wood. Even an
apparently dry branch
gathered from the ground may not yet be dry (especially if it's a
hardwood) so the hot box method described on this page may come in
useful in that case as well. Or even in the case of store bought
wood and you want
to insure that it's been kiln dried before working it. I built the hot box described and pictured on this page for about $15.00 worth of materials. Its simple design is based on one used by master chair maker Russ Filbeck who teaches its use at Palomar College in one of the best woodworking departments in the United States. The heat source is two 100 watt bulbs spaced evenly apart. Their sockets have been inserted, snuggly, through two holes cut into the bottom of the cardboard box. I used two old clamp lights that I had in storage, removing the aluminum shades and the clamps. But inexpensive sockets with electrical cords can be purchased at the local hardware store. Two sections of 2x4s were glued onto the bottom of the box to allow
room
for the light sockets and their
cords. Four dowels were cut and inserted through the middle of
the width of the box, creating a drying rack for the branches.
The box itself I purchased from a local Uhaul store, their "Sport
Utility Model", but any cardboard box can work, if it's long enough to
hold the length of the branches. You can see in the picture how a
lid is cut into the top of the box, which makes it easy to place or
remove branches from the drying rack.The hot box, or "light bulb kiln" as it's sometimes called, dries wood based on the principle of heat convection as well as evaporation. No fan is necessary because of this. You can see in the picture five holes in the lid of the box, each about 1/2" diameter. Each end of the box also has four 1/2" holes, cut at the bottom. With the two 100 watt light bulbs on, the air in the box heats to around 125 degrees, fluctuating between 120 and 130 depending on outside temperature. Moisture then evaporates from the branches and leaves the box through the top five holes (with the lid closed of course), while new, drier air is drawn in from the eight bottom holes. With the branches resting on dowels, the heat flows up and around the branches. Aluminum foil is taped onto the inside lid of the box, helping to deflect some of the heat back down onto the tops of the branches. The result is a very quick, even drying process. Besides being inexpensive and easy to use, the cardboard box also helps to wick out the evaporated moisture. Before placing a bored green branch into the hot box, I like to drill a 1/8" diameter starter hole where the sound hole of the flute will be. This allows air to circulate through the long sound chamber, speeding the drying time and reducing the likelihood of any mold growing during the drying process.
The easiest way to determine when a branch is bone dry (about 5% moisture content) is when it stops losing weight. So I'll weigh the branch before placing it into the hot box, including a short, unbored piece of branch that will end up being the bird or block for the flute. Before weighing, I'll attach a piece of painters tape to each branch with an identifying number and write that number onto a 3x5 card, one for each flute and it's bird. For the smaller flutes I'll weigh every three days, for the larger every week, the weight and date noted on the card. Also included on the card is information about what species of tree the branch came from and where it was gathered. Depending on size and density of wood, bored branches can take anywhere from three days to over a month to dry in the hot box. This to me is preferable to the one year per inch of diameter rule of thumb for air drying.
It's
a subjective thing, but there's an inspiration that happens when I find
a wonderful branch that could become a flute. I want to work it
while that inspiration is fresh. I also feel that something of
the life force or spirit of the tree is still there with the branch
when it hasn't sat so long apart from its tree. When the branch has been determined, through weight monitoring, to be bone dry, I'll remove it from the hot box. This is when I like to apply an oil finish to the inside surface of the air and sound chambers, the bone dry wood allowing deep penetration of the oil. ( I use non-toxic wood oil products from Bioshield.) Later, after creating the nest and flue and thinning the wall thickness where the tone holes will go, if needed, I'll apply an oil finish to the outside. Each branch is unique, so the final finish may vary according to the need or to personal preference. I've had good success with a shellac coat over the cured oil on some flutes. Shellac is great for filling any invisible leaks in the branch that may interfere with the sound quality and tends to brighten the tone by hardening the inner surface of the sound chamber. After the shellac, if any bark needs to be tightened down to the sap wood I'll use CA glue for that purpose. Before voicing the flute, I make sure that the wood will have had time to breath outside of the hot box to achieve the equilibrium moisture content of the shop at 72 degrees. The EMC wherever the flute travels will of course vary. But having had its wood bone dried and stabalized with oil, it should now, with care, safely withstand most livable extremes of temperature, just as it did when physically connected to the tree.