Of the various chucks with movable parts having the power of expansion and contraction, forming the second half of the group for grasping short works by their edges, the spring chucks are the simplest and the most general. The Wood Spring chuck fig. 269, hollow, and slightly taper externally, is rendered elastic by two or several, diametrical saw-kerfs, cut down nearly to the back of the chuck, which latter is strengthened and prevented from splitting by a metal ferrule, fitted around the solid end. Fig. 269, is turned out to fit the work in the same manner as the plain Wood chuck, the sections are then compressed upon it, by forcing a metal ring or hoop up the conical exterior. The most elastic of the spring chucks are made of boxwood, and vary in diameter of aperture from about a quarter of an inch to about six inches, the most useful being for works from about two to four inches in diameter; still larger sizes are occasionally made of other woods. Previously to fitting the work, the ring is pressed on to support the staves, so as to place the chuck under about the same restraint, as when it carries the work; the recess, which is often but a narrow and shallow fillet, is then carefully turned true and flat at the bottom, and the ring having been loosened, the work is pressed down to the bottom of the recess, and fixed, by moderately driving on the ring. Spring chucks are employed for partly finished works, and are particularly convenient for re-chucking work from which no material can be wasted, or, that does not permit of being placed in the plain wood chucks. Among the latter are objects of a fragile character, and others having projections upon their surfaces. The recess being turned of sufficient size to permit the easy introduction of the first, the ring may be pressed on by the hand alone, or by gentle taps at different points of its circumference, given with the tool handle, or by pressing the latter against the face of the ring whilst in revolution ; just sufficient compression can thus be given, without risk of breaking the most delicate work.

Fig. 269.

Chucks With Loose Parts 400230

Fig. 270.

Chucks With Loose Parts 400231

Fig. 271.

Chucks With Loose Parts 400232

Fig. 272.

Chucks With Loose Parts 400233

With work of the second characteristic, when the projections on the surface are small and at regular intervals, the recess is turned of sufficent size to grasp the work by them, and they then indent or slightly cut into the sides of the wood chuck when the pressure is given by the ring. Portions of the chuck are cut away to receive large projections, or for those irregularly placed upon the work, so as to permit the main piece of the latter to be held by the recess. Squares and polygonal figures are carried in a similar manner, the corners of their bases resting on the bottom of the recess, the staves grasping them by their angles; and wood spring chucks are largely used for many purposes in plain and ornamental turning, of which examples will be given.

Metal spring chucks, are made in various proportions in brass and in iron, their application is usually reversed, the end of the work being turned to the size of the rebates or apertures made in the chucks, which are not interfered with; a fair variety of sizes is requisite, that a chuck may always be selected that nearly agrees with the diameter of the work. The more general closely resemble thin, ordinary brass plain chucks, turned with a true internal rebate cut into staves and closed by an external ring. The entire chuck being of metal, it maintains a more constant position on the mandrel and is therefore more trustworthy for turning duplicate pieces with the slide rest, or when the chuck has to be frequently removed and replaced on the mandrel. They are also of advantage when partially finished work has to be laid aside for a period," the work will then sometimes become loose from shrinkage when in an ordinary plain chuck, a great inconvenience, especially in ornamental turning, but entirely obviated by the metal spring chucks. The plain steel ring is generally used to compress the staves, but this is sometimes exchanged for a divided clip ring having a side screw, fig. 270, closing both the ring and the chuck. The ring also sometimes takes the form of a nut on a taper screw, as in fig. 271; this chuck is divided by two long diametrical saw cuts, giving it a small power of contraction, it is strong, and very suitable for holding wires and round objects not exceeding half an inch in diameter. The smaller wire chuck fig. 272, externally a plain taper, is closed by a taper steel ring driven on; various sizes of this chuck screwing into one receptacle chuck.

The metal spring chucks require to be sufficiently rigid to withstand the resistance of the tool upon the work without vibration, their elasticity is consequently slight, which limits their application to works turned to very nearly the same diameter as themselves; and this circumstance has led to some attempts at modification in their construction. The advantages of the metal back and screw for the mandrel, and the more elastic hold of the wood for the work, are sometimes combined, fig. 273; while by one ingenious arrangement fig. 274, the elastic portion of the chuck is separate from that which affords solidity.

In the former variety, a brass flange the back of which screws on the mandrel, is also screwed by its edge into the wooden portion of the chuck, this is turned as a rather thin tube, and cut across by the saw in the usual manner; the back end of the wood tube is strengthened and compressed upon the flange by an external metal band or ferrule, and the staves are closed upon the work as in an ordinary spring chuck; which latter however, the combined form, fig. 273, does not nearly approach in strength. In the second arrangement above alluded to, the chuck is formed of a strong hollow metal cylinder, very similar to the plain chuck fig. 256; but cut externally as a screw, upon which there is a screw ring, having a conical aperture at its front end. Fitting within this chuck, is a thin split brass tube, fig. 274, the front of which is formed as a strong conical flange also split, and of about the same diameter and angle as the aperture in the screw ring. The flange is turned with one or two internal rebates for the reception of the work, and the tube is rendered very elastic by several wide saw cuts which terminate in large holes ; screwing the ring on to the chuck, causes a diametrical contraction of the flange upon the work, while the necessary rigidity is supplied by the intimate contact of the chuck, the ring and the flange. The split tubes may be made as a series, when one chuck provided with two or three tubes fitting one within the other, serves for an increased variety of diameter.