|About the Green-Turning Technique|
Phase One--In the Field
Brad's creative woodturning process commences in the field with a chainsaw as he searches for felled trees having interesting wood grain, color, and figure. Certain woods like maple that have begun to "decay" may exhibit strikingly beautiful patterns and colors caused by fungal spalting. If the spalting is too far advanced, the wood is unworkable. Spalted wood has drastically different densities and requires special care in the turning process, frequent trips to the grinding wheel to sharpen the gouge, occasional applications of small amounts of cyano-acrylate glue (C-A or "Superglue"), and luck. Often a tree has other imperfections that would cause it to be rejected by a commercial sawmill but that enhance the artistic potential, such as bark inclusions, insect or disease discoloration, and the presence of large amounts of sapwood that is lighter in color than the heartwood used for furniture.
A good example of an artistic "defect" is the flame-figure pattern and diagnostic small holes caused by the
ambrosia beetle that literally sucks the life out of certain trees, especially maples. Bark can add beautiful texture and design to a piece.
By using great delicacy and an extremely sharp gouge, a turner may be able to preserve a thin rim of bark on a natural-edge vessel, and this feature, together with the adjacent band of light sapwood, greatly
enhances the beauty of the finished piece and provides a strong sense of the organic whole of the tree's beauty.
The key to success in this first phase of the creative process-the harvesting of the turning stock-- is being able to perceive artistic potential in a large fallen log that may be covered with dirt, vines, bark,
fungal decay and debris, and also a practicable means of cutting and mounting a block on the wood lathe without sacrificing the desirable portions.
Phase Two--Turning Green
Green (wet) wood begins to crack immediately because the moisture evaporates unevenly from the ends and sides of the timber and from areas within the timber of different density, such as the sapwood and tree knots. Damage from cracking and warping may be minimized temporarily by keeping the wood in a plastic bag or under a tarpaulin until it can be rough-turned on the lathe. The rough-turning re-distributes the mass of the wood in a way that lessens differential moisture loss, although the bowl will still crack and deform to a greater or lesser extent depending on the species of wood. Green turning has the advantage, therefore , of reducing the risk of cracking, and it also is a smoother, quieter, and more aesthetic process. The wood is easier to cut, the shavings tend to form in long soft ribbons, not as hard fragments and dust, and the wood is more flexible. There are distinctive spice-like aromas given off by hardwoods in their green state---a good fresh piece of black cherry on the lathe smells almost good enough to eat! (Some woods, however, do have repellent chemical odors.) The key in this rough-turning phase is to remove a sufficient amount of wood from the walls and bottom of the vessel to reduce drying time and potential damage to the piece during moisture loss , but, at the same time, to preserve enough material for re-mounting the piece on the lathe, for cutting the walls back into round, and for excising major cracks. Even when the rough-turned piece is waxed and left on a shelf or placed in a bag to control drying, some deformation and often some cracking will occur. The most vulnerable species of woods and the most delicate turnings need to be monitored closely during the drying process, and first-aid must be given promptly to any emerging cracks in the form of cyano-acrylate glue patches.
Turning a piece of wood on an axis between centers and shaping it with a hand-held chisel supported on a tool rest is a process that dates back to ancient times. Recently, there has been feverish development of new models of lathes, new devices for holding the wood, and new types of chisels for cutting. Although these tools do permit more complex operations to be performed on the lathe, the basic process is unchanged, and many of the finest woodturning artists achieve beautiful results without the most expensive new devices. Brad uses a variable-speed, short-bed (16-inch), Woodfast lathe that allows him close access to the piece from all sides. His primary chisel is a deep-fluted bowl gouge with a drawn-back edge. He also uses fingernail gouges, French-curve scrapers, a small skew, and two simple, Ellsworth hollowing tools, each consisting of a steel bar mounted in thick wooden shaft hewn from an ash or an oak tree, with a cobalt cutting tip inserted into the end of the bar at approximately 0 degrees and 45-degrees. Other essential tools are a grinder with an abrasive wheel designed for high-speed steel, calipers for measuring wall thickness deep inside a hollow forms, and dust collection devices.
Phase Three-Fine-turning, Sanding and Finishing
There are great challenges as well in the fine-turning stage, the first of which is devising a safe way (for the turner and the piece) to attach the progressively smaller and more curved vessel to the headstock (motor-driven end) of the lathe. In order to turn the foot of the vessel after it has been hollowed from the other end, it is no longer possible to glue or screw the piece to a faceplate or, in most cases, even to grip its top with a jaw-chuck. Typically, the turner needs to fashion on the lathe a "helper" form known as a jam-chuck that, on one side, is screwed to the faceplate and, on the other, is pressed against a non-slip material that in turn is pressed against or inside the vessel. The revolving point on the tailstock presses against the center of the vessel's foot and holds this assembly together (hopefully) while it is spinning. Hollow forms are the most tedious and difficult to turn because there is only a small opening through which to extract the shavings and it is impossible to see the progress of the chisel against the inside wall. (Hearing the pitch of the chisel against the wall and tapping the vessel are helpful; stopping the lathe for a caliper measurement after every couple of passes with the chisel is time-consuming and annoying.) The mortality of hollow forms is high. After completing the sanding phase, Brad applies several coats of finishes that enhance the natural grain and color and need no future care other than an occasional polishing with a soft cloth and occasionally a small amount of beeswax, carnauba wax, or vegetable or mineral oil. Brad's two primary finishes are a tung oil formulation and an alcohol-based, FDA-approved finish for salad bowls. Sometimes an alcohol-based sanding sealer is used first to prevent softer and more porous areas of the wood from becoming blotchy. Brad identifies no separate, discrete design phase because with his style of organic turning it is necessary to adapt throughout the process to the appearance of different features in the wood that influence both design and structural integrity. Sometimes the intended bottom of a vessel will become the top or an intended hollow form will become an open form or a large piece will become a miniature.
Woodturning is a moveable feast.
|Copyright © 2006 by Bradford F. Whitman. All rights reserved.|