2014 Green wood turning
Why Turn Green Wood instead of dry or seasoned wood?
There are pros and cons to turning green wood the following are a few:
PROS
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Green wood is readily available and inexpensive
Green wood is easy to turn
Green wood produces little or no dust
One can turn larger pieces from a log without dealing with cracks from the log drying
By rough turning green wood to smaller thicknesses one can speed up the drying process
Turning green wood is fun and fast
Rough turned green wood weighs less and takes up less room as compared to dry blanks
CONS
1. Green wood will warp and change shape, thus turning items such as lidded boxes to finish is
very difficult if not impossible
2. If not taken care of rough turned green pieces may crack, mold or split
3. If care is not taken your tools will rust
4. After all your work you may not end up with a finished piece
5. It takes time to dry and then finish the piece
If you are the type of person that has to start and complete a piece at one go, turning green wood may
not be for you. If you can take a little time each month to turn a few green pieces and set them away to
dry, eventually you will have an inventory that you can draw from to do completion work at one go. In
the long haul finished pieces from green wood take less total time to complete than starting with a dry
blank. Total time includes getting the wood, processing, rough turning , drying and final finishing.
It makes little difference whether one is turning green wood or dry wood, it is very desirable to have an
idea of what it is you want to turn. Not having a vision of what the final form will look like makes it very
difficult to select the right piece of wood for the project. Just putting a chunk of wood on the lathe and
starting to turn is fun, but with a little thought one can begin to turn really interesting pieces. Leaving it
to chance wastes a lot of wood and time and can lead to real frustration. There are lots of books and
the internet is loaded with information on how to select blanks for a specific outcome.
For example let us work through the process of selecting a blank for a simple bowl. Imagine the shape,
is it to be a bird’s beak natural edge, flat oval natural edge, simple curved soup bowl or perhaps a
tapered side rice bowl design. Each of these shapes will come from a blank that looks very different
from the other. Also one should imagine the look of the inside of the piece, do you want undulating
rings or perhaps striking cathedrals in the side wall.
In this example we desire to turn a simple soup bowl shape with gently curved sides. The finished piece
should be between 5 and 6 inches in diameter and 2 ½ to 3 ½ inches tall with a wide foot. The inside
should have cathedrals on two surfaces and half-moon rings on the other. So what should the chunk of
wood look like? The log section should be at least 8 inches in diameter, if the pith is close to the center.
If the pith is off set, the log section should be 7 to 8 inches across the pith with the shallow section
above and the deep section below. The log section should be at least 8 inches long. Cut the log section
into 5 sections . Skim just below the bark on the shallow section and the deep section, then cut the
shallow section just above the pith. Next cut the pith section from the deep section. This will yield two
slices with bark that can be thrown away, the shallow section is 2 inches or so thick and about 8x8
inches. The pith section will be about 1 ½ inches thick with the pith close to the center. This can be
resawn into two smaller sections with bark on one edge and the pith on the other. The remaining
section is the one we will turn it will be about 8x8 and almost 4 inches thick. This blank will yield the 5
to 6 inch by 3 inch bowl.
A word of caution at this juncture: If you have cut the blank on a band saw cutting with the grain you
have produced wood-wool. This must be removed from your band saw. It does not vacuum well and it
will ball up and break the blade or foul the bearings.
The blank can be mounted to the lathe in several methods:
1. Between centers, this is fast and the best way to even up the edges. It is also the least safe and
the most dangerous method.
2. A screw chuck may be used. One drills a hole smaller than the screw chuck and screws the blank
on until it seats against the chuck. One may use plywood washers between the chuck and blank
making it easier to remove after turning, waxing the screw also helps. One may also use an oil
filter wrench to remove blanks once turned. As a last resort remove the blank from the chuck
with the screw still in and mount the blank in the chuck and use a wrench to remove the screw.
If you leave green wood mounted overnight you will have to use this method. The screw chuck
is fast and fairly safe. It is also useful if you are doing a lot of blanks or do not have a drill press.
3. With a drill press and Forstner bit, drill a rebate about ¼ inch deep that is slightly bigger than the
smallest diameter of you chuck. Place the blank on the chuck and expand until firm.
4. Attach a face plate with sheet metal screws to the face of the blank.
Safety note: With all these methods it is desirable to bring the tail stock up and support the blank until
the rough turning is complete on the outside.
Some individuals like to cut the blank round on the band saw , at least knock off the corners. Turning
green wood this is probably not necessary and does not save much, if any, time. Just make sure when
beginning that it is at a slow speed. The blank is balanced and secure and that you have on your face
shield.
Begin shaping the bowl blank starting next to the tail stock and moving to the upper edge. Bowl turning
the outside is SOB- Small outside Big. Never use a roughing gouge in bowl turning. This is the time to
plan your tenon and the shape of the piece. The blank does not have to be turned smooth to finish at
this stage, but one can practice making good clean cuts. Form the tenon to fit the chuck, and make sure
to leave a post or at least a center mark in the center. If a post make sure it will clear the jaws of the
chuck. This will be very important when it comes time to finish the piece. Turn the piece around and
lock it in the chuck, not too much pressure, this is green wood. Face off the blank and remove the
center leaving the blank about 1 inch thick, bottom and sides. Start at the center and work outward to
the edge. Continue to the bottom until the desired thickness is reached. Turning inside is BIS, big inside
to small. Some say to turn until the wall thickness is about 1/10 the diameter. This is ok for large pieces
but the smaller ones may warp too much for a finished piece to be turned, especially in those species of
wood with high shrinkage. The blank is done.
Drying the blank:
The “Rule of Thumb” for air drying wood is ‘one year for every inch of thickness plus one year’. This is a
fair assumption for stacks of stickered wood under a cover outside. One can definitely speed up the
process, but there are some risks. Even stickered dimensional lumber will crack and check. That is why
most dimensional lumber is cut 9 to 10 foot long for 8 foot lumber, the ends are waste. The green
blanks may also check and crack as well as warp. The following are ways of lessening the risk but not
eliminating it altogether. Before starting the drying process it is a good habit to write the date turned,
the wood and weight of the blank on the blank usually on the bottom.
1. Pack the fresh turned blank in “PAPER” bags with saw dust from the turning.
Care should be taken to air the blanks on a regular basis, every one or two days for several
weeks. Leave them out bottom down for about two hours each time. This is true of most of the
methods as well. If you do not do this you may end up with a bag of gray mold and rotten
wood.
2. The blanks may be wrapped in one to two layers of plain paper. This is a good method for those
pieces too big to fit in your sacks. One can use tape to hold the paper on the blank. These
should be stickered and unwrapped and rewrapped every week or so for several weeks. If they
are not stickered they will mold on the surfaces where they touch.
3. Soak the blank in ethanol for several days.
4. Soak the blank in a dish soap solution for several days.
5. Soak the blank in a concentrated salt solution for several days, salt pickle.
6. Boil the blanks in water for about 30 minutes per 1 inch of thickness.
Boiling helps reduce warping, cracking and checking. It can also be used to alter the color of the
blanks and speed up the drying time.
The preferred method is to place the completed blanks in a paper bag made of several layers.
The pieces may also be wrapped individually in paper. Remove the blanks from the bag for 2 to
3 hours each week for 3 to 5 weeks, changing bags as needed to reduce the chance of molding.
After the first 5 weeks the blanks may be removed from the bag and placed in boxes or on the
shelf, or they can remain in the bags until dry. If the blanks are weighed and the weight written
on them at each weighing, the blank is dry when there has not been a change in weight over a
week’s time. Usually this occurs after the blank has lost over a third of its beginning weight.
Depending on where the blanks are kept this may be from 6 weeks to a year. If you have a
forced hot air dryer you can shorten the drying time by weeks if not months.
Some comments about the other methods:
The ethanol soak: it is expensive, a fire and health danger, and the ethanol only lasts for a
couple of treatments. It does speed up the drying process and reduces warping, cracking and
checking.
The dish soap soak: it works ok but, it has a tendency to ferment and rot. It can stink to high
heaven, but other individuals have good luck with it. They claim it makes the wood cut better.
The salt pickle: This method works great, it is cheap, reduces warping, cracking, and checking.
With that said be careful when you turn these blanks, if one does not clean up every bit of chips
and sanding dust, every tool, and metal surface will be rusted the next time you use them. Even
the ones in your tool box. Also the finished pieces have a tendency to form salt crystals on their
surface with changes in humidity.
Boiling is by far the best method to help speed up the drying time, reduce cracking, checking
and warping. It takes additional equipment and time.
It is suggested that one take the time several times a month and rough turn several blanks and
get them started drying. After about six months you will have an inventory of once turned
bowls to start the finishing process. You can finish some and rough turn some and never run out
of dry blanks to turn. One can rough turn almost any form, lidded boxes, vases, urns, bowls,
rolling pins, etc. Small straight spindles may be a problem as there is a tendency for them to
warp too much to be able to finish turning them when they are dry.
A few comments about why taking the pith out of the blank is desirable. Woody plants get
longer at their tips and at any given height, only grows bigger by adding to the diameter. The
wood is youngest and as you approach the center the wood gets older. Also the older wood has
cells that have either collapsed or have been filled with material extracted from the soil. This is
one of the reasons that blanks crack from the surface to the center. The outside layer shrink
more than the center layers and the non- shrinking core act as a wedge. Leaving logs in the sun
uncovered also facilitates star cracking (several cracks going from the surface to the center
around the log). This is caused, in part, by the surface exposed to the sun drying faster that the
shaded surface and temperature differentials.
A green piece of wood cut during the growing season has a specific gravity close to 1, the same
as water. Wet green blanks do not float, or float just below the surface. The contain not only
cell water but also free water or transport water. As you turn these much of the free water is
slung out, this is the stuff that gets all over you and your tools. The inter-cell water slowly
leaves as the blank dries, until the moisture content of the blank is the same as the
environmental moisture content of the air where it is residing. For this reason one must take
care to slow this process down. By placing the blanks is bags and letting their surfaces dry in
bouts over several weeks allows the blanks to reach equilibrium, hopefully without cracks or
checking. Surface checks can occur if the blanks are dried too quickly, sometimes these close
up as the blank completes the drying process. This is why one should not fill cracks on blanks
until they have finished drying. With all this said, some wood species are better suited for
turning and drying green than others. Harvesting wood in the non -growing season is by far the
best time, there is much less free water to contended with. If you like to leave the bark on your
natural edge pieces you should only cut your blanks in the dead of winter. Also in our southern
climates the bark does not stay on all that good, on most tree species, anyway.
Table 1. Tangential and radial shrinkage values from green to oven dry moisture content.
Species
Tangential %
Radial %
American Elm
Sugar Maple
Black Oak
Red Oak
White Oak
Black Walnut
Yellow Poplar
Black Cherry
Sweetgum
Eastern Redcedar
Western Redcedar
White Fir
Eastern Hemlock
White Pine
Ponderosa Pine
Redwood
Spruce
Balsa
Teak
Mahogany
9.5
9.9
11.1
8.9
10.5
7.8
8.2
7.1
10.2
4.7
5.0
7.1
6.8
7.4
6.2
4.5
7.5
7.6
4.0
5.1
4.2
4.8
4.4
4.2
5.6
5.5
4.6
3.7
5.3
3.1
2.4
3.2
3.0
4.1
3.9
2.5
4.3
3.0
2.2
3.7
Tangential shrinkage is the change in width of the wood from side to side. Radial shrinkage is the
change in thickness of wood from the center to the edge. If you can imagine a cube of wood taken
from near the center of a log the growth rings run from top to bottom (longitudinal) , the growth rings
are arranged in bands that run from left to right (tangential), and are stacked from the center outward
(radial). There is almost no shrinkage longitudinally.
Fig.1 Log marked for cutting. The pith is in the
upper left hand corner. The first cut is at the
top, this piece will be discarded. The second cut
is next, just above the pith. This will make
shallow bowls or can be resawn into 2x2s. the
next cut is just below the pith. One can obtain a
6x6x3 blank on the right of the pith, but the
growth rings will be asymmetrical, and 4x4x3
blanks or 3x3s on the left side. The next cut is
done by turning the log over and skimming the
bark side leaving the 14 inch wide slab by 8
inches deep.
Fig. 2 The finished slabs ready to be sealed or
cut into blanks and turned.
Fig.4 Two hours work on the big saw will yeild a
days worth of slabs to process and several days
of turning .
Fig.3 The log on the saw ready for the first cut.