Tc 9-524 fundamentals of machine tools

LAYING OUT AND MOUNTING WORK
There is relatively little layout work to be done for most
lathe work because of the lathe’s ability to guide the cutting
tool accurately to the workpiece. If center holes must be
located and drilled into the end of a workpiece for turning lay
out and center-punch the workpiece using other methods.
Some suggested methods are to use a bell-type center punch
between centers and this cannot be accomplished on the lathe,
(Figure 7-32), use hermaphrodite calipers to scribe
intersecting arcs, use the centering head of the combination
square, or use dividers (Figure 7-33).
7-20

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METHODS OF MOUNTING WORK
Mounting Workpieces in Chucks
When installing the chuck or any attachment that screws
onto the lathe headstock spindle, the threads and bearing
surfaces of both spindle and chuck must be cleaned and oiled.
In cleaning the internal threads of the chuck, a spring thread
cleaner is very useful (Figure 7-34).
Turn the spindle so that the key is facing up and lock the
spindle in position. Make sure that the spindle and chuck taper
are free of grit and chips. Place the chuck in position on the
spindle. Engage the draw nut thread and tighten by applying
four or five hammer blows on the spanner wrench engaged
with the draw nut. Rotate the spindle 180°, engage the spanner
wrench, and give four or five solid hammer blows to the
spanner wrench handle. The workpiece is now ready for
mounting.
Work automatically centers itself in the universal (3 jaw)
scroll chuck, drill chuck, collet chucks, and step chuck, but
must be manually centered in the independent (4 jaw) chuck.
To center work in the independent chuck, line the four jaws up
to the concentric rings on the face of the chuck, as close to the
required diameter as possible.
Mount the workpiece and tighten the jaws loosely onto the
workpiece (Figure 7-35). Spin the workpiece by hand and
make approximate centering adjustments as needed, then
firmly tighten the jaws.
For rough centering irregularly shaped work, first measure
the outside diameter of the workpiece, then open the four jaws
of the chuck until the workpiece slides in. Next tighten each
opposing jaw a little at a time until the workpiece is held
firmly, but not too tightly. Hold a piece of chalk near the
workpiece and revolve the chuck slowly with your left hand.
Where the chalk touches is considered the high side.