finishing cuts. In most cases, one finishing cut is all that is required.
Where exceptional accuracy is required, two finishing cuts are usually used. If the diameter is controlled
manually, make a short finishing cut about 1/2 inch long and check the diameter before completing the
cut.
Because the previous micrometer measurements were made on a rougher surface, some readjustment
of the tool setting may be necessary in order to have the final measurement, made on a smoother
surface, check exactly.
Turning is a lathe operation in which an external cylindrical surface is produced by cutting action of the
tools. The cutting tool is first adjusted for the desired depth of cut, using the cross slide. Then, as the
work piece rotates, the cutting tool is advanced slowly in a direction parallel to the rotational axis of the
spindle and this motion is known as the feed.
By adjusting the feed so that the helical path, and if the tool tip overlaps sufficiently, the cutting tool
removes the excess material and generates a cylindrical surface on the work piece. A spindle rpm that
gives a desired cutting speed at the circumference of the cylindrical surface should he selected. This
may be calculated using the following:
12 X cutting speed, ft/mm
Spindle rpm = ____
pie x work piece diameter (in.)
Feed is measured in thousandths of an inch advance of the cutting tool per revolution of the work piece.
FACING.
Facing is the removing of metal on a flat surface as the result of the tool being fed across the end of the
rotating work piece. The work may be held in a chuck, a faceplate, or between centers. Both ends of the
work that is to be faced must be turned end for end after the first end is completed and the facing
operation repeated.
Because most facing operations are performed on surfaces that are away from the head stock, a
right-hand tool is used most frequently. The spindle speed should be determined from the largest
diameter of the surface to be faced. Facing may be done either from the outside inward or from the
center outward. The point of the tool must be set exactly at the height of the center of rotation. Because
the cutting force tends to push the tool away from the work, it usually is desirable to clamp the carriage
to the lathe bed during each facing cut to prevent it from moving and thus producing a surface that is not
flat.