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Full text of "Modern Mechanical Engineering Vol-I"

EXAMPLES  OF WORK

67

i. CYLINDRICAL WORK

There are certain groups of patterns which possess one feature in common,
that of being jointed through the longitudinal centre. Pipes, columns, and
cylinders of all kinds are typical of a very large number of patterns jointed
thus.

Turning Patterns in
Halves. — Patterns, being di-
vided for convenience of mould-
ing, are jointed and dowelled
before they are turned, since it
would be inaccurate to saw
through solid patterns. Being

, they have tO be Secured             Fig. 25-— Clamping Pattern Halves with Dogs

during turning with dogs (fig. 25) ,

screws (fig. 26), or centre plates (fig. 27). Dogs are driven into the ends in
small and large work alike, in the latter, as an additional reinforcement
to the centre plates. For very light articles the dogs alone may suffice, the

Fig. 26.—Securing Pattern Halves with Screws

centring being done directly in the wood instead of on plates. Screws
are generally used for very light pieces. They are inserted near the ends,
in supplementary portions to be cut off after the pattern has been turned.
If one or two must come also in the body of the pattern, as when it is of
considerable length, the heads
must go in countersunk recesses,
to clear the turning-tools, and
the holes are filled up subse-
quently. Centre plates, smaller
and larger, are used very gene-
rally, not only to secure jointed
patterns, but also to receive the

Fig. 27.—Securing Pattern Halves with Centre Plates

lathe centres in those that are
solid, as these wear the soft
woods when turning is being
done, causing the pattern to run eccentrically.   The plates are made of
iron or brass, and are formed in the smallest sizes like dogs, to be driven
in, but in the larger sizes they are attached with screws or with nails.
' In some cases it happens that jointed pattern portions are less than semi-