Device for grinding a cabachon

Abstract

A dop stick with an oval cabachon adhesively mounted thereon for application to a grinding stone has two axes of rotation, one axis to determine the longitudinal curvature of the face of the cabachon, the other to determine the transverse curvature, and may be moved at random about the two axes of rotation simultaneously without departing from accurate positioning of the cabachon for correctly grinding the cabachon face.

I 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 towards 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.   
     
     
       2. A combination as set forth in claim 1, which includes spring means acting between the base and the support to urge the support forwardly; and   which includes adjustable screw-threaded means to block the forward movement of the support and thereby determine and forward limit position of the support.   
     
     
       3. 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 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;   the second end of said dop stick extending rearwardly from the holder to serve as a handle for manipulation of the dop stick, and said dop stick having a longitudinal slot to straddle the first pivot means. .Iadd. 4. 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 base structure including a normally fixed base member and a support member,   the support member being connected to the base member for pivotal movement of the support member relative to the base member in forwardly and rearwardly directions respectively toward and away from a grinding wheel,   the support member having an adjustable forward limit position;   a dop stick having a head at one end for holding an unfinished cabochon for grinding;   a holder for the dop stick;   first pivot means pivotally supporting the holder relative to the support member;   second pivot means pivotally supporting the dop stick relative to the holder;   one of the pivot means providing for unconstrained manual oscillation of the dop stick only about a first axis of rotation transversely of the dop stick and in the plane of the transverse center line of the plan configuration of a cabochon, and   the other of the pivot means providing for unconstrained manual oscillation of the dop stick only about a second axis of rotation transversely of the dop stick and in the plane of the longitudinal center line of the plan configuration of a cabochon simultaneously with oscillation of the dop stick about said first axis, said second axis being located between the dop stick head and said first axis;   the distance of said first axis from the dop stick head providing the desired radius of longitudinal curvature of the face of the cabochon, and   the distance of said second axis from the dop stick head providing the desired radius of transverse curvature of the convex face of the cabochon;   means for adjusting the distance between the dop stick head and at least one of said axes; and   means yieldingly urging the support member toward said limit position and permitting retraction of the support member from said limit position to avoid damage in the event a grinding wheel should exert a sudden rearward thrust upon a cabochon on the dop stick head. .Iaddend.