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Full text of "Modern Mechanical Engineering Vol-I"

68

PATTERN-MAKING

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circles, as when boss sections have to be fitted on plates or webs. Then a
piece of the web thickness is interposed before the boss is turned, and is
afterwards thrown away.

Flanges and similar attachments are turned in halves, usually dowelled,
and then attached to their bodies. They are held on the face plate with
screws inserted through the plate from the back. The hole is bored entirely
through, or it is recessed, leaving a portion to be removed with the band-saw.

Pipe Patterns.—Pipes and columns have several cardinal aspects in
common. Both are jointed longitudinally, dowelled, and moulded by turning
over. Both are lagged when the smallest diameters are exceeded. Each
has flanges and other attachments fitted. Loam patterns are used for those
of large dimensions. Patterns are plated for quantities. For very large
numbers, metal patterns, unjointed, are employed.

Pipe Patterns for General Service.—It is necessary to make use
of this phrase, because, outside of the general shops, pipes are made by highly

Fig. 28.—Pipe Pattern with Body Flange for Alterations
specialized methods. They are cast vertically. Metal patterns, collapsing
core bars, and a number of special appliances, associated with the moulding,
coring, and casting, are used. In America large numbers of pipes are made
in permanent iron moulds. The methods of making bend and tee-pipes are
similarly specialized.
In the general shops the outstanding feature is that pipe patterns have
to be utilized not only for standard lengths, with flanges, sockets, and spigots
of standard dimensions, but with slight alterations may have to be used for
all kinds of odd jobs and make-up lengths. In these shops therefore it is
customary to keep one set of patterns strictly for standard sizes, and a lot of
odd lengths and nondescript pieces for occasional orders. The cutting and
scheming necessary exercise the judgment of the pattern-maker, and very
much has to be done with stopping-off pieces, which increase the work of
the moulder. In the last case the pattern is not wholly like the casting pro-
duced, the shape of which is revealed by the stopping-off pieces supplied
and the corresponding sectional parts put on the pattern.
Pipe flanges are fitted into recesses turned between the termination of
the body and the core prints (fig. 28). A flange being retained correctly in
its recess need not be screwed in place. For casting shorter lengths, a body
flange A is screwed on, and this indicates the length at which the mould has
to be stopped off. The stopping-off piece supplied carries the half-core
print. Socketed pipes are stopped-off by providing an iron socket piece