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Full text of "Modern Mechanical Engineering Vol-I"

208

THE   MACHINE-SHOP

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. x  X

SIDE ELEVATION

BACK £L£I//\T/OA/

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are clamped in pairs, and lie parallel in recesses at the opposite end, where
they are brought up against an abutment piece. The ends to be bevelled
project beyond the vees, where they are milled with a cutter, divided, in order

to permit of readjustment
with packing as the edges
wear.

Example of a Box Jig-
fixture.—Figs. 42 and 43
give the principal elements
of a fixture by Messrs.
Ruston & Hornsby, Ltd., of
Lincoln, used in machining
the body of a check valve.
Its characteristic feature is
the provision made for drill-
ing a large number of holes
at different angles. The
valve, enclosed in the fix-
ture, is located by a flange
which enters the shallow
recess in the bottom, and
is secured by the jig cover.

Fig. 43.—Drilling Bush set at Angles in a Locating Block           The   inside   of the   COVCr  IS

recessed to receive a flange

on the opposite end of the valve body. The four bushed holes arranged
in a circle in the bottom and in the cover guide the drills for the bolt
holes in the flanges. Two other holes are drilled at angles through the
bushes A and B, to permit of which the fixture has bevelled feet at a and b.

During the vertical drill-
ing, bevelled packing
pieces are inserted under
these edges. The round
hole c receives bushes
that interchange for drill-
ing and tapping holes.
The oblong recess D re-
ceives the locating block,

Fig. 44.—Hinged Cover for a Fixture containing Four Drilling             ,            ,         ,      ,  ,£         >.

Bushes at different Heights                                  Shown detached (tig. 43 ),

that   carries   a   drilling

bush at angles in two directions. The fixture is then stood at the required
angles on a bevelled support. The holes E and F receive bushes to guide
drills for holes in the body.

Fig. 44 is the cover of a fixture through which holes are drilled at different
heights in the body of a feed pump. It is hinged at the left, and clamped
at the right with an eye-bolt in an open slot. Nuts are not run off their
bolts, only slackened.