NOVEMBER/DECEMBER 1983, No. 43, $3.50 Making ... - Wood Tools

This 8-in·. dia. marnut bowl on East Indian rosewood stand looks as if it were made on an ornamental lathe, but the spiral
decorations were freehand-carved on the edge of a stationary disc sander.
lip of the bowl. I also make a mark around the bowl's largest
diameter. This line will be the point where the spiral changes
direction. It is also the circumference around which the spacing
of the spirals is marked.
So that the spirals will be spaced evenly, I have mounted
on the outboard side of the lathe a 12-in. plywood indexing
plate. This plate (marked off in 28, 32, 40 and 48 increments,
or however many you want) is a substitute for the
lathe's smaller indexing plate. It is screwed to an outboard
faceplate, offering a wider choice of indexing patterns and
more control over tolerances. A pointer damped to the lathe
stand allows me to hold the bowl in position for each layout
line. The spiral offers endless possibilities, but a good place to
start is with 12 increments. As many as 24 increments work
well on bowls up to 6 in. in diameter. I lay out each spiral
with a compass pivoting from a block of wood damped to
the tool rest. Experiment with the compass and various toolrest
positions, looking for a pleasing sweep. Once decided,
pencil an arc from the bowl top to the bowl center, crossing
through each index mark. Reposition the tool rest on the other
side of the lathe to complete the bottom of the arc, from
the high point to the foot. Remove the turning, still attached
to its faceplate, and examine the scribed lines to make sure
that the layout is both accurate and aesthetically pleasing.
Now I move to the disc sander. This is the same plywood
disc I have mounted outboard for an indexing plate: I cement
24-grit aluminum oxide (doth-backed, resin bond) to
the outside face and run the lathe at 300 RPM to 500 RPM.
The slow speed affords better control for initial cutting, and
the large diameter keeps the disc operating cool and also pre-
vents the paper from excessive loading. The edge of the disc is
beveled at 30° toward its back side, so that there is a defmite
edge for cutting precise V -grooves. I cut with the outermost
X in. (or less) of the wheel, arcing the stock down along the
edge, rather than pushing it straight in. I aim my cuts between
the lines, trying to leave the pencil lines intact .as reference
until I approach finish-sanding. Disc-sculpting requires
careful, measured, graceful movements, so it is important that .
you are seated comfottably, that your posture is relaxed and
that your workspace is well lighted. Grip and wrist motion
must be consistent so that all passes are equal. Therefore, you
must maintain total concentration, without interruptions.
The first cut is very shallow and defmes the basic form of
the groove. Go once around the whole bowl, cutting about
'li6 in. deep in each groove. The second pass cuts deeper and
wider into the established groove. You are now committed.
Sometimes it takes only two passes to cut the desired arcs,
sometimes as many as five. In this phase it is essential that
each cut be equal and in sequence-never backtrack. Irregularities
are better worked out with finer grits. It is also important
to keep dear of the top and bottom guidelines; taper out
the grooves later, with a fmer-grit disc.
In the next phase I use an 8-in. Power Pad (available
through Power Pad Mfg., 1223 W. 256th St., Harbor City,
Calif. 907 10) to refine form and to remove scratches. This is
an industrial-quality foam disc that's flexible enough to sand
contours easily. It's available in soft, medium and hard consistencies;
I use mostly soft and medium. I cut my own sanding
discs for the Power Pad from aluminum oxide and silicon
carbide paper. It's less expensive than using pre-cut discs, but,
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