Modern Mechanical Engineering Vol-I

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88

PATTERN-MAKING

method is that of ramming a few teeth in a core box, and laying the cores
round a circle. The wheel machine includes a dividing apparatus with
change gears for all pitches, and mechanical slides for withdrawing the
segmer.tal blocks that carry two, three, or more teeth.
Two designs of machines are made, one having a
moulding table on which the smaller gears are moulded
in top and bottom boxes, the other having the me-
chanism carried on a column sunk in the floor, in the
sand of which the teeth are moulded, to be covered
with a plain top box.

Fig. 61.—Tooth Block in
Mould

Fig. 62.—Sweeping Board for a Spur Wheel

The Pattern Parts.—The essentials, varied in details with the class
of gear and the sections and outlines of arms, &c., are the tooth block, the
sweeping boards, and the core box.

Tooth Blocks.—A tooth block is like part of a wheel rim having a few
teeth cut on it, attached to a backing of suitable shape and dimensions, and

I screwed to the tooth carrier of a
machine. The simplest blocks are
those for spur (fig. 61) and bevel
gears, which are withdrawn vertically.
Those for helical, double helical, and
worm wheels are withdrawn in the
horizontal direction, except in those
machines which do not include this
provision. For use in these, the
pattern-maker divides the block,
separating the main backing from the actual teeth, which are carried on
a thin backing, and dovetailed loosely to the portion that is attached to
the carrier. The latter is first lifted vertically by the machine, followed
by the teeth, taken away horizontally with the fingers.

Sweeping Boards.—These (fig. 62) are necessary to form a bed to
receive the cores, to make the joint faces at their correct heights between
drag and cope, to indicate the radii of the teeth, and, in the case of bevel

Fig. 63.—Sweeping Board for a Bevel Wheel