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THREE PHASE STEP-BY-STEP PROCESS
Phase 1-Rough Turning A Side-Grain
Blank 1. With a
chain saw, cut a green log the length equal to the
diameter of the log and then cut it down the middle.
Removing 1inch beyond the pith, if you are not going to
turn it immediately. If you are not going to turn it
immediately paint the ends with some type of end sealer
or latex paint to reduce checking. [Notice, if you are
going to process the logs for later turning, cut the log
2 inches longer than the diameter of the log, split the
log removing 1 inch either side of the pith and coat the
ends with end sealer]
2.
Determine the grain orientation on the blank. If it is
to be a natural bark edge hollow form, the top of the
form will be at the bark side and the bottom of the form
is toward the pith.
3. To
rough out the hollow form blank- Draw a circle on the
bottom of the blank to determine the diameter of the
bowl. Matching the size with a plywood disk, which is
mounted and centred on the bark side of the blank.
Place the blank on a band saw with the pith side on the
band saw table and cut around the disk. Or rough it out
using a chain saw.
4. Mount
the rounded rough blank between centres with the bark
edge at the headstock and the pith end at the tailstock.
Make sure it clears the lathe bed and tool rest by
manual turning the blank 360 degrees. Visually
re-arrange the headstock and tail stock positions until
at least the high sides are equal and if possible the
lower sides also. At least two of the sides should be in
the same plane for a balanced design.
5. Rough out the shape of the hollow form between centres, using
the tailstock for safety, at a low lathe speed. Since
the form is turned green, it will warp as it dries, so
only the rough shape is needed at this stage. It is
important at this stage to get the design of the form
correct and accurate. NOTE-After the interior is
removed, it is almost impossible to change the design. The largest part of the hollow
form should be in the top or bottom 1/3 of the form not
in the centre.
6. Using a
rough out gouge or a 5/8 inch bowl gouge held at
approximately 30 degrees up from horizontal, present the
bevel until it rides the blank and raise the handle to
pivot the cutting edge into the work and sweep the tool
through an arc until it begins to cut. The flute of the
tool will lie about at 45 degrees of vertical. The bevel
does not have to ride the piece at this point. Rough out
from the bark edge to the base or you will knock off the
bark when turning it. Roughing speed on the lathe should
be at a low speed, about 500-800 RPM's. Stop the lathe
frequently to check your progress and to move the tool
rest closer to the blank. Always make sure you are
supporting the cutting edge. Take
care that you never present an unsupported edge of a tool to the wood, you
will get a catch. This is because when there is no support beneath the edge of
the tool, the downward force of the rotating wood snaps
the tool over.
7. Refine
the design of the hollow form when it is in balance at a
higher speed 900-1000 RPM's, using a more sensitive cut
(sheer cut). Apply thin layer super glue to the bark
edges after the hollow form profile is completely
established, if it is to have a bark edge.
8. Prepare the base of the
blank to be fitted with a faceplate or a chuck. If the
form is very shallow, you can glue a scrap block onto
the bottom with Yellow glue or Polyurethane glue (it
works best because it needs moisture for it to cure).
Let the glued blank dry over night, placing it in a bag
or sealing the outside with end sealer better to do
both. Failure to protect from drying will cause
cracking. It is a shame to put all of this effort into a
piece and have it crack because of carelessness.
9. Mount
the blank on the faceplate or chuck to remove the
interior of the form by hollowing. You are now ready to rough
turn the interior of the form. This is the hardest part
of this exercise since you will be "turning blindly
inside the form". You can drill a 1 inch hole in the
centre of the form to a depth of 1 inch from the bottom
of the form blank or use a boring bar to make this cut.
This provides a depth measure when removing the centre
of the form.
10. Check
the form blank is running true before turning the lathe
on. Now is the time to get it running true by re-turning
the sides of the form, if necessary. Keep the tailstock
against the form blank for safety. When it is running
smooth, you can remove the tailstock.
11. Interior hollow turning- Rough out the inside of the
form to about 1 inch thickness. Starting with the inside
of the hollow form (where the depth hole is) continue to
remove the interior in a scooping motion using the body
to support the tool and moving in a dance-like motion
around the bowl. This movement is from right-to-left
(from the lathe bed toward the head stock in a
continuous motion) after you have cleaned the interior
all you can with a straight tool, you then proceed to
hollow with a curved tool as the interior of the form
becomes wider and deeper. Since you are hollowing the
form through a narrow opening, (This
requires a steady hand! Go slow and remove the waste
often since accumulation will bind the tool causing it
to rip from the chuck and destroy the piece. This can be
done with an air hose, by hand or using a coat hanger as
a "scraper").
12. When a
uniform thickness of 1 inch is achieved. Remove the form
from the lathe and coat the interior edge of the bark
with super glue. Coat both the interior and exterior of
the form with end sealer and place in a bag paper or
plastic on a shelf to air dry. Weigh the rough form and
record the weight. Turn the hollow form bag inside out
and place the form back in the bag and record the weight
at least every two days. When the form no longer loses
weight, it is stabilized. It can be further dried in a
microwave (this technique is for another article). It
should be at about 10-12 percent moisture content to
finish turning. Kiln dried lumber is 8-10 percent
moisture. Average drying time is 90- 120 days depending
on conditions and the type of wood. The same procedure
can be achieved with the use of a moisture meter.
Phase 2-Finish Turning
13. Remount the dried blank on the lathe. It will have
warped so that the faceplate will have to be remounted,
re-chucked or re-stabilized. This can be done between
centres again by using a reverse chucking method. Finish
turning the outside of the form so that it runs true and
refine the design. Finish sanding the outside of the
form on the lathe either by power sanding with a drill
or by manual holding the sand paper against the bowl as
it spins. (MAKE SURE YOU FOLLOW ALL SAFETY PRECAUTIONS
FOR THIS TECHNIQUE.) Sand through the grits starting at
100 through 400 grit. Coat the outside of the bowl with
one coat of DEFT semi-gloss lacquer. Let it set 3
minutes and wipe with a cloth. Turn the lathe on and
burnish with the cloth or with shavings. Make sure you
protect the lathe bed against splatter.
14. Finish
turning the inside of the form from the edge to the
centre of the bowl removing 1/8 to 1/4 inch at a time.
Finish to 1/4" to 3/8" in uniform thickness in the walls
and a little thicker in the bottom. Sand the interior
and DEFT coat it like the outside of the bowl. Mark the
interior bottom of the form on the outside of the hollow
form to indicate the interior's depth. Remove form from
the lathe. Remove the faceplate.
15. Repair
any missing bark with the excess bark saved from the
interior part of the bowl. Attach it with thick super
glue and accelerating spray.
16.
Reverse chuck the finished form. (Mount a smaller form
on the faceplate and mount it on the headstock this is
called a Jam chuck. Cover this form with a piece of
carpet pad or leather to prevent "burning" and to
provide a friction pad to drive the hollow form.) Place
the neck of the hollow form against the jam chuck and
tighten the tailstock against the bottom of the form.
With the lathe at slow speed, make a concave impression
on the bottom of the form, making sure not to cut
through or make the bottom too thin. The bottom of the
form before it is finished should be twice the thickness
of the sidewalls plus the length of the screws holding
it to the faceplate. The bottom of the form should be
about the same thickness as the side walls when
completed. For example, if the wall thickness is 1/4"
thick then the bottom before finishing should be 1/2"
thick. When it is finished turned and sanded it should
be about 1/4" thick. Sand with the same grits as the
rest of the form. Sign an date with a Sharpie pen. Coat
the bottom lightly with spray Deft lacquer. Let it dry 2
hrs.
Phase 3-Finishing the Hollow Form
17. Coat
the entire form with another coat of DEFT lacquer. Wipe
dry after 15 minutes setup time, Let dry over night.
18. I use
a jeweller's finish on my bowls and hollow forms. This is
a technique that uses buffing wheels and compounds to
get the desired finish. This process is:
A. Tripoli wheel charged with
red Tripoli is used to remove excess finish and to
smooth the outside of the form.
B. Coat the inside and outside
of the form (anywhere you can reach) with a paste wax
that has high carnauba content. Let it set for 30
minutes and buff off with the wax wheel charged with
pure carnauba wax.
Thanks to Maurice Clabaugh
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