Precision matthews PM-1127VFI-LB, Safety & Training Manual

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Independent Chuck
The independent chuck generally has four jaws which are
adjusted individually on the chuck face by means of adjusting
screws.
The chuck face is scribed with concentric circles which are
used for rough alignment of the jaws when chucking round
workpieces. The final adjustment is made by turning the
workpiece slowly by hand and using a dial indicator to
determine it's concentricity. The jaws are then readjusted as
necessary to align the workpiece within the desired tolerances.
The jaws of the independent chuck may be used as illustrated
or may be reversed so that the steps face in the opposite
direction; thus workpieces can be gripped either externally or
internally.
The independent chuck can be used to hold square, round,
octagonal, or irregularly shaped workpieces in either a
concentric or eccentric position due to the independent
operation of each jaw.
Because of its versatility and capacity for fine adjustment, the
independent chuck is commonly used for mounting odd-shaped
workpieces which must be held with extreme accuracy.