Tc 9-524 fundamentals of machine tools

Precision Facing
Special methods must be used to face materials to a precise
length. One method is to mount the work in a chuck and
lightly face one end with a cleanup cut. Then, reverse the
stock and face it to the scribed layout line. This method may
not be as accurate as other methods, but it will work for most
jobs. A more precise method to face a piece of stock to a
specified length is to turn the compound rest to an angle of 30
degrees to the cross slide and then use the graduated
micrometer collar to measure tool bit movement, Figure 7-48.
At this angle of the compound rest, the movement of the
cutting tool will always be half of the reading of the graduated
collar. Thus, if the compound rest feed is turned 0.010 inch,
the tool bit will face off 0.005 inch of material. With the
compound rest angled at 30°, a light cut may be made on the
first end, then the piece reversed and faced to accurate length.
Always lock the carriage down to the bed. This provides the
most secure and accurate base for the cutting tool and helps
eliminate unwanted vibration during facing operations.
Another way to face to a precise length is to use the lathe
carriage micrometer stop to measure the carriage and tool bit
movement. Using the micrometer stop can sometimes be
faster and easier than using the compound rest graduated
collar for measuring tool bit movement.
7-28

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TC 9-524
STRAIGHT TURNING
Straight turning, sometimes called cylindrical turning, is the
process of reducing the work diameter to a specific dimension
as the carriage moves the tool along the work. The work is
machined on a plane parallel to its axis so that there is no
variation in the work diameter throughout the length of the
cut. Straight turning usually consists of a roughing cut
followed by a finishing cut. When a large amount of material
is to be removed, several roughing cuts may need to be taken.
The roughing cut should be as heavy as the machine and tool
bit can withstand. The finishing cut should be light and made
to cut to the specified dimension in just one pass of the tool
bit. When using power feed to machine to a specific length,
always disengage the feed approximately 1/16-inch away
from the desired length dimension, and then finish the cut
using hand feed.