THE OVAL CHUCK.

Progress, 1 October 1907, Page 454

THE OVAL CHUCK.

The oval chuck almost requires to be seen to be understood, but a general notion of its appearance and action may be gained from Fig. 1. Its object is to impart such a motion to the work that a tool held stationary in contact with it shall at each revolution of the mandril describe an ellipse instead of a circle The right hand portion of the figure will be seen to bear much resemblance to an eccentric chuck A* plate (b) has upon it a similar boss (scarcely seen in the figure), by which it is attached to the mandril ; and a similar slide (c) has a screw for carrying an ordinary chuck containing the work, at the base of it being a wormwheel and tangent screw, as before. These last are better omitted when the chuck is to be used for plain oval turning only, the screw being then part and parcel cf the slide (c), so that one source of possible unsteadiness is avoided. Instead of the slide (c) being adjusted by the the slow motion of a screw, as in the eccentric chuck, it is made to work in its groove with perfect freedom, carrying with it, however, two guides (aa), which are firmly fixed to it, and which pass through slots in the plate (b) Entirely detached from the above plate, slide, etc , is a ring, of which the outside diameter exactly fits the space between the guides (aa) By means of the arms and milled- headed screws on the left of the figure, this ring can be firmly fixed to the headstock of the lathe without in any way interfering with the rotation of the mandril, the screw of which passes through the ring. As long, therefore, as this fixed ring is concentric with the mandril, the oval chuck in no way influences the motion cf any piece of work which may be attached to it, its guides (aa) merely sliding round the ring without being drawn out of their natural course. But when this ring is moved sideways by loosening one of the pointed screws and tightening the other, so that its centre no longer coincides with that of the mandril, it mor no longer allows the guides (aa) nor flthe shde (c), which is in connection with them, to follow a circular path. At two points, indeed, during each revolution of the mandnlj[(when a line joining the centres of the guides is vertical, the arms and screws being horizontal when the ring is m position), the slide (<) is concentric with it , but after these points have been passed, the guides alternately draw the slide more and mere from its natural course, till it has an amount of eccentricity equal to that at which the ring has been set. This occurs twice m each revolution ; and, since the effects of these two disturbances are in opposite directions, the major axis of the ellipse thus described exceeds its minor axis by twice the amount of eccentricity given to the ring By means of graduations on any convenient part of its arnr=, the amount can be read off. It must of course be equal to half the difference between the major and minor axis of the ellipse Thus, for cutting an ellipse measuring 1\ x 6 inches, the ring must have an eccentricity of f- of an inch In using it with handtools and an ordinary T-rest, considerable care is necessary to keep the edge of the tool at one constant height above the lathe-bed. Any change in the height of the tool causes a corresponding change in the direction of the ellipse, accompanied by the destruction of the work.