Turning a Calabash BowlComments (0)
Many people ask me if the wood I make bowls from is green
wood. The answer is always “yes.” However, there’s more to the story. In order
to make large bowls, you have to start with a green piece of wood. That's
because it would be rare to find a dry piece, say, 5" thick × 12"
wide that does not have a crack in it. (Such cracks in salad bowls make them
filler for the rubbish bin.) So the trick is to take the green blank, rough it
into a bowl shape that is 10% as thick as the diameter, seal it with an appropriate
sealer, and store it away for slow drying. Later, after the rough bowl has
fully seasoned, you turn it to final shape and wall thickness. The downside
here is the painfully long wait; roughturned bowls take from months to over a
year of drying time.
However, there’s another way to work with green wood and make very handsome bowls without going through the interminable drying process. That is to turn what I loosely call a “calabash bowl.” This is a Polynesian term for a gourd. It is essentially a baseless bowl carefully extracted or cut from the log to create a visual balance after the bowl has dried. In my opinion, bowls generally do not need bases to be functional. Another reason: if you make a traditional based bowl from green wood, it usually will not sit flat after it dries. So, let’s make a calabash and explore the joy and secrets of green wood turning.
Note: For my green
wood calabash, I choose a variety of white oak (Quarcus lobata), known as a
California Valley oak. Oak is a good choice since you can find it throughout
North America. Plus, due to its difficulty in drying, the woodturning community
shies away from it for their seasoned turnings. For me, white oak for bowls
(especially a calabash) is underrated. Its medullary rays can look stunning!
Creating the blank
1 Start with a fresh round log about 14" in diameter and at least 14" long . (I’m using one I cut from a windfall tree on a vineyard near my farm.) Select a cylinder-shape log that doesn’t have knots or other defects. Now, study both ends of the log, noting the pith and any radiating cracks that may affect the bowl blank. Avoid including the pith (the log’s center) in the bowl. Mark a cutline with a black marker on the log's end so its annual rings and sapwood will be balanced evenly in the finished piece. (See Figure 1, Cut 1.) This also helps in the drying process.
2 Chainsaw the log almost in half where marked (Photo A), splitting it through the pith. That way, the log still sits firmly on the ground for Cut 2. If uncomfortable using a chainsaw, split the log at a bandsaw using a right-angle sled. (See the sled in “Harvesting Backyard Exotics” in the Oct/Nov 2014 issue, page 33.)
3 Cut a flat on the bottom of the log (Cut 2) so the blank
will sit flat on the bandsaw (Photo B). Finish cutting the log in half.
4 Make a round hardboard or plywood template the diameter of the desired bowl. (While every bowl blank will be a different size, this one is 6" high and 14" across). Mark the template's center and the center of the half log’s top face. Secure the template by driving a nail through its center and into the log’s center.
5 Rest the log half on the bandsaw table and cut out the
blank, running the blade along the edge of the template as you rotate the blank
(Photo C). Note: For the best results, I use a 1⁄2" × 3 TPI (teeth/inch)
6 Remove the template, and, using a drill, bore a 3⁄8" hole 13⁄4" deep into the blank’s nail hole to accept a screw center (Photo D). Work to keep the bit at a right angle to the blank’s face.
Safety Note: There is a lathe speed formula by the late Utah turning teacher Dale Nish that he used to help students turn safely; I recommend it here. It goes like this: The diameter [of the turning] x rpm should equal between 6000-9000. For instance, if you have a 10"-diameter piece and your lathe is spinning at 1000 rpm, you are at 10,000, and over the safety limits for that project.
Mount the blank and turn the outside
1 Install a four-jaw chuck onto your lathe’s headstock, and tighten a screw center into it. Install a live cup center into the tailstock. Now, screw the blank onto the screw center, and bring up the tailstock to secure the blank.
2 Now, with the lathe running at 800 rpm, use a 1⁄2"
bowl gouge with a fingernail grind to round the blank (Photo E). Move the tool
back and forth on the tool rest while riding the bevel. Note that when turning
fresh green wood there will be water spraying from the blank as it spins. This
is part of the fun. The moisture keeps your tool cool and is not as abrasive on
the tool’s edge as seasoned wood. For safety, I stand forward of the turning as
3 Next, angle the tool rest and begin shaping the bottom of
the bowl by removing the waste wood, using a 1⁄2" bowl gouge (Photo F).
4 Form a 1⁄4" tenon on the bowl’s bottom to fit in your four-jaw chuck (Photo G). To perform this step safely, make the tenon around 40% of the diameter of the bowl blank if possible. Here, the tenon is about 6" for the best possible grip. (See the buying guide for the chuck and jaws needed. If using a smaller chuck jaw opening, make sure that the blank size is one you can safely handle.) I turn the tenon with a 3⁄8" fingernail spindle gouge. Its deep grind makes it suitable for detail work. I shape the tenon so it is at a right angle to the bowl bottom, which is flat at this point. This lets the face of the chuck fit snugly against the flat bottom.
5 With the bowl blank held firmly in the chuck and the
tailstock still in place, true up to the finished calabash shape (see Figure
2), using a series of shear scrapes. I try to make a typical calabash shape
that is slightly enclosed to create a pleasing look after it dries.
Turn the inside
1 Remove the tailstock and fit the tenon in the four-jaw chuck on the headstock. Locate the tool rest so that it is parallel to the top face of the bowl blank and just below center. Now, flatten the face with a 1⁄2" bowl gouge. Then, begin to hollow the interior of the bowl with the gouge (Photo H). Start near the center of the blank, and take a series of cuts, working from left to right in the order in Figure 2. Make deeper and deeper cuts until most of the bulk is removed. I carefully leave more bulk at the bottom of my piece so I can make cuts on the upper portion of the bowl without losing structure to make those cuts.
2 Note: At this point, you want to establish the wall
thickness. Since this is a green-finished bowl, aim to cut the walls evenly and
relatively thin to help with the drying process. Uneven walls and thick wood
invites cracking during the drying process. Using a 3⁄8" bowl gouge,
establish a wall thickness of 3⁄16" as shown in Photo I. To do this, I cut
down from the rim one third of the depth of my bowl and stop. Now, make sure
you are cutting the wood evenly and cleanly. If you like what you see, cut the
next one third down until you blend that with the first third. Proceed to blend
in the bottom one third. I'll use a 1⁄2" bowl gouge that has been
traditionally ground to finish this task. That’s because the grain direction
changes from the sides to the more end-grain-like wood at the center, which the
traditional grind handles better than a fingernail grind.
3 Remain very conscious of the depth of the bottom. I make
that judgment by eying the outside shape and determining where the outside
bottom will be. Since I am shooting for a 3⁄16" wall thickness, I make the
inside 3⁄16" from my perceived exterior’s bottom. I also want a continuous
flowing curve on the inside that mimics the exterior shape. This takes patience
and thoughtful measuring with a caliper throughout the process (Photo J).
Sand and complete the calabash
1 With the tool work done for now, it’s time to sand your calabash. I use 3"-diameter Mirka Abranet mesh sanding discs attached to a 3" foam pad accessory for a portable drill. (I prefer Abranet over traditional sandpapers because the mesh abrades green wood faster and smoother. I also protect myself from sanding dust with a respirator.)
2 Before sanding and with the piece stationary, carefully
examine the surface areas that have torn grain or tool marks. Then, with the
lathe running at 500 rpm, sand the bowl’s inside surface, as shown in (Photo
K). Once you smooth out the troubled areas, spin the piece and sand over the
entire surface inside and out. I start with 120 grit and sand through 400,
going over the inside and outside surfaces within reach. Carefully clean the
bowl with compressed air between sanding with each grit. Don’t overheat the
wood during this process. Green wood can create heat-checking, which can ruin
your project. Apply the sanding mesh lightly to the wood, and replace the discs
as soon as they lose their cutting/sanding ability.
3 Next, remove the finely sanded calabash from the lathe and make a jamb chuck from a piece of scrapwood that you screw on to a faceplate (Photo L). Using a 3⁄8" spindle gouge, cut a 3⁄8"-long tapered tenon on the jamb chuck that fits snugly inside the rim of the completed bowl. Test-fit the bowl to get the size just right.
4 Further secure the bowl by holding it in place with the tailstock and live cup center. Then, finish shaping the bottom of the bowl (Photo M). Sand as before. Remove the tailstock and take some delicate cuts to trim off the last bit of wood at the center. Sand the area. This approach will let you give your baseless bowl better balance when it rests on the table.
Dry the calabash and apply a finish
Note: While you dodge months of drying by turning a calabash, a little careful drying is still critical. And, since oak is particularly hard to dry, you need to slow the process down at this point.
1 Place the bowl in a thick paper sack from the grocery store and leave it in a cool dark place for a few days to a week. Since the piece is thin-walled, it should be dry by then. If you have a sensitive scale, one way to know is to weigh the bowl after a day or two and keep weighing it until it stops losing weight. You could also use a moisture meter provided you don’t mar the surface.
2 Finish the calabash once it is dry. Notice how the dried
calabash has warped. It has moved into an organic shape that is very pleasing
to the eye. To finish the piece, first determine how you see it being used and
the wood’s color. If I am making a decorative calabash, I go with a tung oil or
shellac. If the wood is a light color, I avoid these finishes since they may go
yellow over time. Gloss polyurethane works well on a lighter wood. I see the
bowl I turned here as a utility item and will therefore use a penetrating oil
finish like walnut oil. Penetrating oils are better for utility items since
there is no film to harm while cleaning. Also, penetrating oils require no
skill to apply and can be restored by anyone. Once the finish dries completely,
put your calabash to work.
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