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Full text of "Modern Mechanical Engineering Vol-I"

THE  ELEMENTS

59

flat. The method adopted therefore is to drive into the adjacent edges
tightly-fitting dowels, which prevent the faces from getting out of level.
The strips are maintained in one plane by the attachment of flanges, ribs, or
other pieces, as in fig. 10, or, if
these do not happen to be avail-
able, then temporary battens are
screwed across, the impressions
of which are " stopped-off " in
the mould. An alternative to
this, which can be adopted when
the plated portion lies horizon-
tally, is to make an open frame,
jointed at the corners, and to fill
up the interior with loose strips

(%• 7)-

Boxing-tip.—This, except in
narrow widths, is combined with
open jointing. It is adopted in
all rectangular sections that are
too large to be cut from solid
plank, and is the only way in
which swelling and shrinkage
can be avoided in these. Longi-

Fig. 10.—Portion of Boxed-up Bed, showing Open Joints
and Cross-bars

tudinal strips are screwed to
cross-bars, a single strip for
narrow sections, several strips
with open joints for the larger
dimensions.

In these constructions the vertical pieces should occupy the entire depth
of the pattern, as in fig. n A, B, and should never lie between the top and
bottom plates, as in fig. n, c. The reason is, that the delivery of the
first is clean, that in the second is not, because a very slight shrinkage of

B

Fig. ii.—Right and Wrong Ways of Boxing-up

the strips produces lapping edges that tear up the sand.   Also it is better
to fit the pieces with a rebated shoulder (A) than to make abutting joints
only (B).
Cylindrical Articles.—These include engine cylinders, pump barrels,