The several foregoing plain, wood chucks, are principally used for carrying partly finished works, already possessing a circular margin; and they acquire so little vibration under the turning tool, that they are particularly suitable for turning smooth surfaces and for finishing work. The elasticity of the wood affords a firm hold without indenting or damaging the surfaces, and the wood chucks are readily adapted by the turning tool to the particular diameter; but to prevent turning them to waste, a variety of sizes is necessary, that a chuck may always be selected that previous turnings have reduced nearly to the required size. The general convenience of the wood and metal driving chucks leads to their very extensive use, and in the following particulars of their management, many points may be observed that also necessarily apply to other chucks and to turning generally.
In rechucking the work, which may have been previously mounted in a metal chuck, between centers or otherwise, while the one end has been turned true and to the required form, it is necessary in order to ensure the entire piece possessing one uniform axis, that this true end when rechucked in the wood chuck, should again run exactly true or revolve upon the same axis as before. It cannot however do this, unless the chuck itself be exactly concentric with the axis of the mandrel; and this is attained in the most simple manner, by turning the chuck away to the size required by the work, when the true adjustment of the latter in the true chuck, perfectly maintains the one uniform axis throughout the work.
The quasi-cylindrical aperture, as also the external fitting for the reception of the work, is turned carefully true and very slightly, or about 2° taper; the edge upon the surface of the chuck, being also turned true. Internally, the aperture in the wood chuck usually terminates in a flat surface, upon which, and especially towards its edge more or less care is bestowed as may be required for the particular work in hand. The external fitting, figs. 257. 262, meets a narrow vertical margin or surface, called a "shoulder," and this is generally required to be turned accurately flat, under the guidance of a square.
The more usual application of the plain wood chuck is temporary and to individual works, and the mere alteration required to fit the work, at the same time renders the chuck p 2 true. But, when a wood chuck is used continuously for any special purpose, especially such as require accuracy, its comparative want of permanence of form due to atmospheric influence, requires correction from day to day; hut a shaving removed from its different surfaces with a tool held very steadily, at onces restores its perfect truth. The work is very frequently pressed into the wood chuck by the fingers and adjusted to truth by them alone; but when greater hold is required it is obtained by light blows, given by the tool handle or hammer upon the end of the work, as with the metal plain chuck; still less force being used, to avoid risk of splitting the chuck or of damage to the work.
Any error in the truth of adjustment in the chuck of long pieces, is sufficiently obvious, a piece of chalk, or a turning tool applied towards the extreme end, detecting the high point for correction. With many works of moderate length, the finished portion contiguous to the chuck is observed while in revolution, and the mouldings or other projections turned upon it, are compared with the true edge of the chuck, and the one adjusted to the other by pressure or taps with the tool handle. When the work is short or thin, the error is less easy of detection; the adjustment can then sometimes be materially assisted, by turning a portion at both ends perfectly true, when the work is between centers or in its other first chucking; these two parts are necessarily parallel and possess one axis, consequently at the second chucking, it is only necessary to test and adjust to truth the accessible part previously turned, to ensure the agreement and truth of the part concealed within the chuck.
The truth of the work is also frequently attained by its being placed in contact with the true surface of the recess, or the shoulder of the rebate ; but in this case the work is pushed into the chuck by the fingers, the ball of the thumb, or the end of a tool handle, and not driven; for should blows be employed, the work may strike the bottom and rebound from the elasticity of the materials, the more so the greater the force employed. The truth of adjustment of bright works in metal is easily tested by the reflection of any fixed object; which should appear perfectly at rest, when seen in their rounded edges, or other curved surfaces, that have been previously turned true.
For work that is fragile and can bear but little compression, the chuck is turned away to permit its comparatively easy introduction; the edges of the rebate being then rubbed as they revolve with a piece of chalk, to assist the hold upon the work. When by accident the work has been misfitted, and the chuck does not permit of further turning, one or two thicknesses of paper may be placed between them as a remedy; the paper is sometimes placed over the chuck in a single piece like the head of a drum, or it may be used as narrow strips or ribbons placed radially. In unchucking from either the wood or metal driving chucks, if the work be long, a few light blows of the hand, the end of a tool handle or a mallet, given upon the side of the work towards the end, and continually at different parts of its circumference suffice to release it. For very short pieces, the chuck may be unscrewed from the mandrel and held in the hand with the work uppermost, when a sharp blow from a hammer struck upon the margin of the chuck, will cause it to fall out from the reaction. Occasionally a piece of hardwood is inserted through the screw of the chuck and struck against the end of the work. At other times the edge of a turning tool placed against or beneath, any projecting edge upon it, is used as a lever to prize it out of the chuck. Should any of these methods appear likely to damage the work, or when that is too firmly fixed for easy removal, the wood chuck should be turned away with a parting or flat tool, until the portion holding the work is reduced to a thin shell, when it can be readily removed with the fingers.