(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Modern Mechanical Engineering Vol-I"

PATTERN-MAKING

Fig. 32.
Pipe Joints at Right Angles

is used instead of a dovetail (fig. 33), or to reinforce dovetails (fig. 31).
Abutting joints are reinforced with dowel-pins fitting tightly, and with
screws put in diagonally. Flanges, sockets, and spigots are fitted as in straight
pipes, and stopping-off is practised.

The larger pipes and bends, and those of
awkward shapes, for which the demand is
limited, are frequently moulded from loam
patterns, for which the pattern-maker supplies
strickles and fittings. As the principal work
is thrown on the core-maker and moulder,
the subject is reserved for treatment in the
article on Foundry Work.

Column Patterns.—These are only made
solidly when of small diameters, say not ex-
ceeding 4 in. or 5 in. Beyond these, and
apart from quantity methods of moulding,
they are always parted longitudinally along
the centre and dowelled. Solid timber is
rarely used when the diameter exceeds 6 in.
or 7 in. The reason is that the stuff is liable
to become convex or concave in the joint

faces, and the pattern to lose its circular section. It is also liable to warp
and curve lengthwise, an evil that results from the incessant wettings of
the joint faces with the swab.

Patterns from about 6 in. in diameter upwards are, like the larger pipes,
built with " lags " or strips of timber screwed on cross-bars (fig. 34) and

glued to each other with longitudinal joint
edges. No rules can be stated for the cross-
sectional dimensions of lagging strips, nor
for the spacing of the cross-bars. These
are proportional to the diameter and the
length of the column, but are never very
thick nor very wide, since, as in segmental
work, the object sought is to localize shrink-
age as much as possible. The cross-bars
must be set at distances sufficiently close to
one another to sustain the lags bridged over
them against the pressure of ramming.
Thus the stiffness of the pattern must be
secured without unduly increasing the timber
sections. A little experience teaches the pattern-maker how to proportion
these details, the relations of which are correctly proportioned in the
accompanying drawings.

When building up divided columns, the cross-bars for one half are laid
down on a true joint board, and the lags are fitted to that first. They are
planed on faces and abutting edges, the latter being chalked to show contact,

Fig. 33.—Iron Plate for Pipe Joints