Tc 9-524 fundamentals of machine tools

7-27

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TC 9-524
to the outer edge if a right-hand finishing tool bit is used.
Avoid excessive tool holder and tool bit overhang when
setting up the facing operation. Set the tool bit exactly on
center to avoid leaving a center nub on the workpiece (Figure
7-46 ). Use the tailstock center point as a reference point when
setting the tool bit exactly on center. If no tailstock center is
available, take a trial cut and readjust as needed. If using the
cross slide power feed to move the tool bit (into the center),
disengage power when the tool bit is within l/16 inch of the
center and finish the facing cut using hand feed.
Facing Work Between Centers
Sometimes the workpiece will not fit into a chuck or collet,
so facing must be done between centers. To properly
accomplish facing between centers, the workpiece must be
center-drilled before mounting into the lathe. A half male
center (with the tip well lubricated with a white lead and oil
mixture) must be used in the lathe tailstock to provide
adequate clearance for the tool bit. The tool bit must be
ground with a sharp angle to permit facing to the very edge of
the center drilled hole (Figure 7-47). Start the facing cut at the
edge of the center-drilled hole after checking for tool bit
clearance, and feed the cutting tool out to the edge. Use light
cuts and finishing feeds, which will reduce the tension put on
the half male center. Replace the half male center with a
standard center after the facing operation, since the half male
center will not provide adequate support for general turning
operations. Only a small amount of material can be removed
while facing between centers. If too much material is
removed, the center-drilled hole will become too small to
support the workpiece.