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Full text of "Modern Mechanical Engineering Vol-I"

78

PATTERN-MAKING

i I

g> 4.5.—Alternative Methods of Jointing Bottom Flange of
Trolley Wheel

prevent slipping of a rope, which also is provided for in a core box rather
than in the pattern.

Trolley or truck wheels resemble sheaves in the fact that the presence

of double flanges (fig. 2)
entails the employment
of a three-part box. Only
the lower flange is left
loose. This may be done
in either of the ways
shown (fig. 46). When
vertical arms are fitted,

either to trolley or sheave wheels, they are screwed fast in the bottom, but

left loose in the top, to come up with the cope and be withdrawn therefrom.

Pulleys.—Patterns of wood are useless for pulleys.    They must be

of iron. And, except
for repetitive work, they
are not made with rim,
arms, and boss in one
solid piece. Each is a
separate element, rim
and arms in iron, and
bosses in wood, from
which pulleys having
different widths of face,
and bosses for any
bores required can be
made up.

The system adopted
is to have a large stock
of pattern rims, turned
inside and out, with a
very slight taper and no crowning, of maximum depths likely to be
required, say of 12 in. width of face in the smaller sizes and 16 in. to
18 in. in the larger. Widths narrower are produced by stopping-off in the

mould. Diameters may advance
by i in. in the first, and by 3 in.
in the second. When the volume
of trade is large, one series of light
pattern rims and one of heavy is
stocked. The arms are made of
cast iron to fit easily within the
Fig. 48.-Core BOX for Fly-wheel Arms              rims< These also are made light,

having only the elliptical section,

and heavy with shallow vertical ribbings.   The bosses of wood fit to any of

the arms with a standard size of stud in a centre hole, say if in. diameter.

From these elements the moulder produces pulleys of any widths of

* 47-—Pattern of a Fly-wheel