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

Page: 23 / 34

Universal Scroll Chuck
The universal scroll chuck 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 work
for concentric turning. This chuck is not as accurate as the
independent chuck, but when in good condition it will center
work within 0.002 to 0.003 inches of runout.
The jaws are moved simultaneously within the chuck by a scroll
or spiral-threaded plate. The jaws are threaded to the scroll and
move an equal distance inward or outward as the scroll is
rotated by the adjusting pinion. Since the jaws are individually
aligned on the scroll, the jaws cannot usually be reversed. Two
sets of jaws, one for internal work and one for external work are
supplied with the chuck.
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.