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Full text of "Modern Mechanical Engineering Vol-I"

19*

THK   MACHINE-SHOP

is considerably exceeded. Since, as a rule, cutters are used for general
service, the speeds, depths of cut, and feeds are varied to enable them to
work with efficiency on all materials. Only in the most general terms can
these be hinted at. Soft steel can be cut at peripheral speeds of from
90 to 150 ft. per minute; the harder steels from 65 to 75 ft.; cast iron,
Ho to 100 ft.; the brasses and bronzes up to 1000 ft. per minute. Depths
of cut may range from iV, to J in. in one traverse. Feeds, formerly so
low as 2 to 3 in. linear feed per minute, are frequently now from 12 to

Mill

i.fttl

SECTIONAL
, a5,--Two Cuftefi in €**ng, with Diiunce-piece

20 in. The metal removed in a minute with a cutter 8 in, wide working
on mild has amounted to 23 c. in., and on cast iron to 48 c, in.
End Mills*—In          (fig. 23) the end teeth cut, and those on the side
smooth the surfaces. The teeth are straight for working on brass, for other
materials they are spiral This provides a cutting rake, or, when the spirals
arc* left-hand, the rake is negative with the tendency to hold the tool hack
in its spindle. These tools only cut on the Inner ends of the teeth in the
11 centre-cut mills **, which have teeth on the inside, so that in these the tool
can be vertically to the required depth, and then traversed. End mills
are provided with               taper             or they are          fitting on arbors.
Form Cutters.—These include               angular              for cutting
and veefcl             the tee-slot               angular cutters for produc-
ing the           of            the very                             employed for grooving
a           groupy employed for fluting the drills.,                and