Device for grinding a cabachon

Claim 1

In a device to facilitate the grinding of the face of a cabochon of generally elliptical plan configuration to a curved convex configuration by a grinding wheel, the combination of: a dop stick to hold an unfinished cabochon on one of its ends; a holder for the dop stick; a base structure; first pivot means on the base structure pivotally supporting the holder for manual oscillation thereof about a first axis of rotation in the plane of the transverse center line of the plan configuration of the cabochon; and second pivot means on the holder pivotally supporting the dop stick for manual oscillation relative to the holder about a second axis of rotation in the plane of the longitudinal center line of the plan configuration of the cabochon; the distance of the first pivot means from the desired convex face of the cabochon being substantially equal to the desired radius of longitudinal curvature of the convex face of the cabochon, the second pivot means being located between the cabochon and the first pivot means, the distance of the second pivot means from the desired convex face of the cabochon being substantially equal to the desired radius of transverse curvature of the convex face of the cabochon; whereby, when said device is positioned for use and the face of an unfinished cabochon on said dop stick is brought into proper grinding contact with said grinding wheel, the holder and dop stick are simultaneously movable about the above-mentioned first and second axes of rotation so that said face can be smoothly ground to said curved convex configuration; said base structure including a normally fixed base and a support carrying the first pivot means; the support being pivotally mounted on the base and having a normal forward limit position; said base structure also including means yieldingly urging the support toward its limit position and permitting retraction of the support from its limit position to avoid damage to the device in the event the rotary grinding wheel exerts a sudden thrust against the cabochon.