LATHE OPERATIONS - OD1645 - LESSON 1/TASK 1
made by turning the workpiece slowly and using gages to determine its
concentricity.
The jaws are then readjusted as necessary to align the
workpiece to desired tolerances.
(b) The jaws of the independent chuck may be used as in figure 14, 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 he used to hold square, round, octagonal, or irregular shaped
workpieces in either a concentric or eccentric position due to the
independent operation of each jaw.
(c) Because of its versatility and capacity for fine adjustment, the
independent chuck is commonly used for mounting workpieces that require
extreme accuracy.
(3) Universal Scroll Chuck.
(a) The universal scroll chuck (figure 14 on the previous page) usually
has three jaws which move in unison as an adjusting pinion is rotated. The
advantage of the universal scroll chuck is its ease of operation in
centering the work for concentric turning. This chuck is not as accurate as
the independent chuck but, when in good condition, it will center the work
automatically within 0.003 of an inch of complete accuracy.
(b) The jaws are moved simultaneously within the chuck by means of a
scroll or spiral threaded plate.
The jaws are threaded to the plate and
move an equal distance inward or outward as the scroll is rotated by means
of the adjusting pinion.
Since the jaws are individually aligned on the
scroll, the jaws cannot be reversed. However, the chuck is usually supplied
with two sets of jaws which can be interchanged.
(c) The universal scroll chuck can be used to hold and automatically
center round or hexagonal workpieces.
Having only three jaws, the chuck
cannot be used effectively to hold square, octagonal, or irregular shapes.
(4) Combination Chuck.
A combination chuck combines the features of the
independent chuck and the universal scroll chuck and can have either
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