he cutting of the groove of
the spiral proceeds. A groove may also be cut in two pieces of stock and
glued together to form a hole through the stock.

2. Turn a cylinder 2-1/2" in diameter, tapering it to 1-1/2" at the one
end; this part should be 12-1/8" long. Both ends should be left larger
than 2-1/2" as the lower and upper designs must be cut here.

3. Let the spindle revolve in the lathe and draw circles as shown in the
layout (Plate B-V--2-a'). The number of circles will vary with the
taper. Since seven turns are needed in the present spiral, 28 circles
will be necessary--four circles for each turn of the spiral as shown in
the middle diagram. A good proportion to follow is to measure the
diameter of the spindle at circle 2 and lay off this distance from
circle 1 to circle 3. Then measure the diameter at circle 4 and lay off
this diameter from circle 3 to circle 5 and so on until all circles have
been made. Then divide these large divisions into four equal parts.

4. Draw four lines the entire length of the spindle, each 90 deg. apart as
shown by the heavy lines in the middle diagram. The heavy circles of the
same diagram represent the complete turns of the spiral.

5. Lay out the line representing the ridge of the spiral as shown in the
middle diagram. Begin on circle 1, where the straight line crosses it,
draw to circle 1' at the point where the next straight line crosses it,
then to 2--2'--3--3' and so on until the end is reached. This forms the
ridge of the spiral as shown in diagram 3. Next it may be more
convenient to draw another line representing the groove. In this case
begin at point X in the middle diagram, opposite the point where first
started, and continue in the preceding manner, making this line parallel
to the other line.

6. Saw on the line last made, being careful not to saw too deeply. The
depth must be 1/4" less than half the diameter of the spindle where the
cut is made. This saw cut forms the groove of the spiral. The groove is
then cut out by hand with a chisel or knife, by working down the wood on
both sides of the saw cut. After the spirals have been roughed out, a
rasp is used to finish shaping them. The work is then sandpapered
smooth, while the spindle is revolved slowly in the lathe.

7. Cut designs on the ends of the cylinder and polish.

PLATES B-V--2-b, b'. DOUBLE SPIRAL. TAPERED SHAFT

To work out a double spiral for the electric lamp illustrated in Fig. 25
proceed as fo