Tc 9-524 fundamentals of machine tools

Turning Work Between Centers
Turning work that is held between centers is one accurate
method that is available. The chief advantage of using this
method is that the work can be removed from the lathe and
later replaced for subsequent machining operations without
disturbing the trueness of the turned surface in relation to the
center holes of the workpiece. The lathe centers must be in
good condition and carefully aligned if the turning operation
is to be accurate. If necessary, true the centers and realign as
needed. After the workpiece is center-drilled, place a lathe dog
(that is slightly larger in diameter than the workpiece) on the
end of the work that will be toward the headstock, and tighten
the lathe dog bolt securely to the workpiece). If using a dead
center in the tailstock, lubricate the center with a mixture of
white lead and motor oil. A ball bearing live center is best for
the tailstock center since this center would not need
lubrication and can properly support the work. Extend the
tailstock spindle out about 3 inches and loosen the tailstock
clamp-down nut. Place the work with the lathe dog end on the
headstock live center and slide the tailstock forward until the
tailstock center will support the work; then, secure the
tailstock with the clamp-down nut. Adjust the tail
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TC 9-524
of the lathe dog in the drive plate slot, making sure that the tail
does not bind into the slot and force the work out of the
center. A good fit for the lathe dog is when there is clearance
at the top and bottom of the drive plate slot on both sides of
the lathe dog tail. Tension should be applied to hold the work
in place, but not so much tension that the tail of the lathe dog
will not move freely in the drive -plate slot.
Check tool bit clearance by moving the tool bit to the
furthest position that can be cut without running into the lathe
dog or the drive plate. Set the lathe carriage stop or
micrometer carriage stop at this point to reference for the end
of the cut and to protect the lathe components from damage.
Set the speed, feed, and depth of cut for a roughing cut and
then rough cut to within 0.020 inch of the final dimension.
Perform a finish cut, flip the piece over, and change the lathe
dog to the opposite end. Then rough and finish cut the second
side to final dimensions.