EXAMPLES OF WORK
their connecting passages. The upper view is a cross-section, the lower
is one-half the pattern open in the joint face. Head metal is provided.
The lags, the flat strips, the battens, bosses, and prints are obvious.
Fig. 44 gives complete views of the pattern for a Diesel engine cylinder
cast in one with its A-legs. The whole of the interior is formed with cores.
The upper portion A, the cylinder, is lagged and turned as a separate section,
and is united to the pattern frame B with two dovetails. B is boxed-up on
three cross-bars, being formed with strips having open joints. The feet are
attached to this, as shown in the lowest view, which is a plan taken from the
top of the cylinder, and the print is fastened to the bottom of the pattern.
Two diagonal brackets are fitted loosely with skewers, and four hold-down
bosses that lie below the joint of the pattern are left loose, with drop
prints. A bracket c at the top is prepared separately, with the print for
its lightening core, and attached to the cylinder.
2. SHEAVES, PULLEYS, AND FLY-WHEELS
The features which sheaves, pulleys, and fly-wheels possess in common
are: their outlines are circular, their depths relatively shallow, and they have
central arms (or discs), through the centres of which the moulds and often
the patterns have to be parted. The shrinkage stresses in arms and rims
cause fracture in these castings unless the pattern-maker exercises care in
proportioning of parts.
Sheaves.—Patterns for these are made in wood (fig. i) for moderate
numbers of castings, in metal
(fig. 45) for quantities. When
wood is used the rims are
built up with thin segments,
the centres being made in a
similar manner when they
are SOlid-plated. Arms are Fig. 45 .—Iron Pattern for Sheave Wheel
locked at the centre and let
into the rim, these methods being identical with those employed in the con-
struction of toothed wheels. Patterns are divided through the centre of
the arms, or these are left of the full thickness, and the upper portion of the
rim is registered to the lower (figs, i and 45). Moulding is generally done in
a three-part box. the joints being made in the planes a, a (fig. 45). But a
circular grid can be used, as shown at the right hand, to carry the sand in the
recess, and then a two-part box with its joint at b can be used. Alternatively,
an annular core print can be fitted around the rim, and a series of short
lengths of core laid in. This is seldom done when complete patterns are
made, except in the case of cupped wheels which are provided with recesses
to receive the links of chain that lie flat and edgewise alternately. But the
method is of value when very large pit wheels are made with wrought-iron
arms, in which case the entire rim, interior as well as exterior, is frequently
formed with cores. Another form of sheave is that with a wavy gorge to