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Full text of "Modern Mechanical Engineering Vol-I"

74

PATTERN-MAKING

work proceeds. Some pattern parts have to be left loose, fitting with
dowels or skewers. The locations of these are determined by the method
of jointing and moulding adopted, this being settled by the pattern-maker*
In some cases, alternatives present themselves, in others only one method

Fig. 39.—Example of Fluted Strips attached to an Iron Backing

is practicable. Usually the most convenient and the safest method of
setting and securing the cores determines the choice. A very slight degree
of inaccuracy in setting, or due to shifting from position in casting, will
produce spoilt work. Moulds are divided horizontally, because it is easier
to set cores thus than in a vertical mould of small diameter. But it is set

vertically to be poured,
in order to float all
sullage up into the head
metal, which if present
on portions to be tooled
would spoil the casting.
Typical Patterns.
—In the plainest cy-
linders the steam-chest
is distinct from the
main body, and a flange
on the latter is provided
to receive it. When

practicable, the flange is always moulded downwards, because it is con-
venient to insert the cores for the passages in the bottom of the mould,
instead of in the joint face. Prints are attached to the flange, and this is
necessarily dowelled loosely to the passage block. The cylinder foot, when
at right angles, is made fast to the body. But it may happen that other

Fig. 40.—Cylinder Pattern with Steam-chest