FORM WORK, MODELING.
=58. Making a Cylinder.=--The cylinder is evolved from the square prism
by increasing the number of sides until a prism is formed with so many
sides that its surface can be easily transformed into a cylinder by
means of sandpaper.
[Illustration: FIG. 109.]
(1) Begin by making a square prism which shall have the same dimensions
for its width and thickness as is desired for the diameter of the
cylinder. (2) Change this square prism to a regular octagonal or
eight-sided prism by planing off the four arrises. The gage lines which
indicate the amount to be taken off of each arris are made by holding
the gage block against each of the surfaces and gaging from each arris
each way, two lines on each surface. These lines must be made lightly.
The distance at which to set the spur of the gage from the head is
equal to one-half the diagonal of the square end of the prism. Fig.
109. Since the ends are less likely to be accurate than any other part,
it is advisable to get this distance as follows: Lay off two lines on
the working face a distance apart equal to the width of the prism.
These lines with the two arrises form a square the diagonal of which
can be measured and one-half of it computed.
[Illustration: FIG. 110.]
Carpenters in working on large timbers lay the steel-square diagonally
across so that there are twenty-four divisions from arris to arris.
They then mark off the timber at seven and seventeen inches. Fig. 110.
These numbers, while not mathematically correct, are near enough for
practical purposes. In planing the arrises off, the piece may be held
in the vise or placed against the bench-stop. Fig. 111. Care must
be taken not to plane over the lines, for not only is the one side
enlarged, but the adjacent side is lessened, thus exaggerating the
error. (3) Judging with the eye the amount to take off, plane the eight
arrises until there are sixteen equal sides.
[Illustration: FIG. 111.]
Again plane the arrises, making the piece thirty-two sided. On a small
piece this will be sufficient; if the piece is large, the process may
be continued until the piece is practically a cylinder. (4) To finish
a small cylinder wrap a piece of sandpaper around it, rub lengthwise
until the surface of the wood is smooth and the piece feels like a
cylinder when revolved in the hand.
=59. The Spokeshave.=--Fig. 112. The spokeshave is used principally to
smooth curved surfaces. It may be drawn toward or pushed away from the
worker, whichever is more convenient. By means of screws, the blade
may be adjusted to take light or heavy shavings. The spokeshave is
practically a short plane with handles at the sides, and in using it
the aim should be, as with the plane, to secure silky shavings of as
great length as the nature of the work will allow.
[Illustration: FIG. 112.]
=60. Making Curved Edges.=--To make curved edges on a board,
finger-gage on each side lines which shall indicate the amount of
curvature. Fig. 113.
[Illustration: FIG. 113.]
If the curve is to be a gradual one reaching from one of these lines
over the middle of the edge to the other two lines should also be
finger-gaged on the edge. Finger-gage from each side using a distance
equal to one-fourth the whole thickness of the piece.
[Illustration: FIG. 114.]
[Illustration: FIG. 115.]
With the spokeshave, Fig. 114, carefully cut off the two arrises to the
pencil lines so as to form two bevels. This gives three surfaces to the
edge of the board. Estimating the amount with the eye, cut off the two
arrises formed by these three surfaces until five equal surfaces are
formed in their place. This process may be repeated until the surface
of the edge is practically a curved surface. With a piece of sandpaper
held as shown in Fig. 115, rub until the surface is smooth and evenly
curved.
=61. Modeling.=--This term is used to apply to the method of making
objects of such irregular form that the judgment of the worker must be
depended upon to give the correct result without the aid of gage and
knife marks. The forming of a canoe paddle or a hammer handle are good
illustrations.
[Illustration: FIG. 116.]
Generally a little forethought will show a way in which the piece of
work may be partly laid out with knife, square and rule. To illustrate,
take the hammer handle, Fig. 116. The steps would be as follows: First,
plane a face side and a face edge, and square the two ends so that the
piece shall have the length desired for the finished handle. Second,
draw a center line on the face side, parallel to the face edge and lay
off on either side of this the two straight lines which shall indicate
the amount of taper; also sketch in the lines of curvature. Plane the
two edges to the tapering lines and square with the face side. Then
cut to the curved lines, keeping this surface also square with the
face side. In a similar manner, lay off on the face edge a center line
parallel to the face side, mark the taper and lines of curvature, and
work these surfaces as in the second step. Third, the piece may be laid
off still further by drawing on the larger end the form of the ellipse
which that end is to assume. With spokeshave, judging the curves of the
middle with the eye, work out the desired form. The steel scraper is
to be used for finishing after the piece has been made as smooth as is
possible with the spokeshave.