2.]

B-III--8-a. Sphere

After the sphere is turned as nearly perfect as is possible when working
between centers (Steps 1 to 4) it is cut free from the waste stock and
is centered in a chuck.

The chuck is made of any soft wood and should be cut in the end grain,
which will insure equal pressure on all sides. Equal pressure cannot be
obtained if the Chuck is cut in cross grain wood, owing to the tendency
of side grain to give more than the end grain. The sphere should be
forced into the chuck with slightly over half protruding. Very thin cuts
should be taken and the sphere should be revolved one-quarter turn after
each until true. As the sphere becomes smaller during the cutting, it
will be necessary to cut the face of the chuck down and bore the hole
deeper and smaller in order to keep more than half of it protruding at
all times.

[Illustration: Mirror (See Pages 299-301).]

To remove the sphere tap the chuck lightly with a hammer just above it,
at the same time pull out on the sphere.

CHAPTER XI

SPIRAL TURNING

Spiral turning is a subject that has received very little attention by
most schools in which wood turning is taught. Spiral work is seen in
antique furniture and also in the modern furniture of the present day.
It seems that it takes the wheel of fashion about a century to make a
complete turn, for what our forefathers neglected and destroyed the
people of the present day value and cherish.

Spiral work gives excellent practice in shaping and modelling wood. It
brings into play the principle of the helix as used in cutting threads,
etc.; and its form, size and shape may be varied according to the taste
of the individual. As in threads so in spiral work we have single and
double spirals, and their form and proportion depend upon their use and
application in furniture making. A variation of the spiral may be made
in several ways: First, by changing the number of turns of the spiral on
a straight shaft; second, by running a spiral on a tapered shaft; third,
by changing the shape or form of the spiral itself; and fourth, by
making more than one spiral on a shaft. It is uncommon to see ten or
twelve spirals running around a single shaft.

Some of the forms of the above types are fully taken up and explained in
the work that is to follow.

PLATES B-V--1-a, a'. SINGLE SPIRAL. STRAIGHT SHAFT

To work out a single spiral for a pedestal proceed as follows:

1. Turn a cylinder 2-1/4" in di