nute.
3.1416 x 5

If the diameter is simply multiplied by 3 and the fractional part is
omitted, the calculation can easily be made, and the result will be
close enough for practical purposes. In case the cutting speed, for a
given number of revolutions and diameter, is wanted, the following
formula can be used:

_R_[pi]_d_
_C_ = ----------
12

Machinists who operate lathes do not know, ordinarily, what cutting
speeds, in feet per minute, are used for different classes of work, but
are guided entirely by past experience.

=Feed of Tool and Depth of Cut.=--The amount of feed and depth of cut
also vary like the cutting speed, for different conditions. When turning
soft machine steel the feed under ordinary conditions would vary between
1/32 and 1/16 inch per revolution. For turning soft cast iron the feed
might be increased to from 1/16 to 1/8 inch per revolution. These feeds
apply to fairly deep roughing cuts. Coarser feeds might be used in many
cases especially when turning large rigid parts in a powerful lathe. The
depth of a roughing cut in machine steel might vary from 1/8 to 3/8
inch, and in cast iron from 3/16 to 1/2 inch. These figures are intended
simply to give the reader a general idea of feeds and cuts that are
feasible under average conditions.

Ordinarily coarser feeds and a greater depth of cut can be used for cast
iron than for soft steel, because cast iron offers less resistance to
turning, but in any case, with a given depth of cut, metal can be
removed more quickly by using a coarse feed and the necessary slower
speed, than by using a fine feed and the higher speed which is possible
when the feed is reduced. When the turning operation is simply to remove
metal, the feed should be coarse, and the cut as deep as practicable.
Sometimes the cut must be comparatively light, either because the work
is too fragile and springy to withstand the strain of a heavy cut, or
the lathe has not sufficient pulling power. The difficulty with light
slender work is that a heavy cut may cause the part being turned to bend
under the strain, thus causing the tool to gouge in, which would
probably result in spoiling the work. Steadyrests can often be used to
prevent flexible parts from springing, as previously explained, but
there are many kinds of light work to which the steadyrest cannot be
applied to advantage.

The amount of feed to use for a finishing cut might, properly, be either
f