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Full text of "Modern Mechanical Engineering Vol-I"

222

THE   MACHINE-SHOP

finish-bored on the next, and reamed in a third, with possibly a finish reaming
to follow. The fixture retains the casting accurately, and a jig locates and
coerces the boring bar.

When a casting includes more than one cylinder bore the same system is
adopted. But here the single-spindle machine is at a disadvantage. Twin
and multi-cylinders, therefore, cast en bloc, are better dealt with in machines
having as many spindles as there are bores, all operating simultaneously.
The boring or reaming of two, four, or six cylinders occupies no more time

Fig. 57.—Two Distinct Pieces of Work being tooled on one Machine

(p. 223!

than that of one. Then, to avoid loss of time in changing of tools and altering
speeds and feeds, work if held in a fixture can be transferred between adjacent
machines for rough- and finish-boring and reaming.
Boring and Turning Mills.—These are strictly lathes in which the
axis of revolution of the work is vertical. They afford conveniences relating
chiefly to the chucking of work on a horizontal face plate and to the very
large diameters that can be dealt with thus. The advantages are most
apparent when a number of separate pieces have to be set up, and when a
piece of work requires loose packing, bolts, and clamps instead of being
gripped in chuck jaws. And, when articles are not concentric, counter-
balancing necessary in the common lathe is not required in the vertical
machine. Another point in the vertical machines is that the work tables
are well supported, and provision is frequently included when doing light