Tc 9-524 fundamentals of machine tools

Turning an Eccentric with Center Holes
Before an eccentric workpiece can be machined, it is
necessary to center-drill both ends of the workpiece, including
the offset centers. If the workpiece is large enough to position
all center axes on the work at the same time, the machining
operation will be simple and easy.
7-62

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TC 9-524
First determine the stock required by adding the throws
plus 1/8 inch for machining (Figure 7-102).
Face the work to length in a chuck.
Remove the piece and apply layout dye to both ends.
Mount the work in a V- block and, using a surface plate
and venire height scriber, lay out the normal center axis
and the offset center axes on both ends.
Accurately prick punch the intended centers, check for
accuracy, and then enlarge the punch marks with a center
punch.
Center- drill both sets of center punch marks by using a
milling machine, a drilling machine, or the four-jaw
independent chuck of the lathe with a dial indicator to line
up the centers.
Mount the work in the lathe between centers and turn the
largest diameter first. If all diameters are the same, turn
the middle diameter journal first.
After turning the center journal down to the required
diameter, remount the work in an offset center hole and
machine the throw diameter to the finished size.
Accurately prick punch the intended centers, check for
accuracy, and then enlarge the punch marks with a center
punch.
Center- drill both sets of center punch marks by using a
milling machine, a drilling machine, or the four-jaw
independent chuck of the lathe with a dial indicator to line
up the centers.
Mount the work in the lathe between centers and turn the
largest diameter first. If all diameters are the same, turn
the middle diameter journal first.
After turning the center journal down to the required
diameter, remount the work in an offset center hole and
machine the throw diameter to the finished size.
Additional throws are machined in the same manner. Throw
positions may be started by cutting with a parting tool to
establish the shoulders, which may aid the turning operation.
The tool bit selected will depend on the material to be
machined and on the depth of cut desired.