This invention relates to pantographs or other devices for forming copies and, in particular, proportionally reduced copies, of three dimensional objects from solid blocks or blanks. Although these machines are used in a variety of applications, they are especially useful in the areas of stone and metal forming, where it may be impractical or impossible to form an exact facsimile from a mold.
Although various suitable devices exist for copying forms in two dimensions, the problems inherent in making exact copies of three dimensional models have yet to have been adequately solved. Typically, quality material removal pantograph machines are expensive, bulky and hard to manufacture. On the other hand, smaller, less expensive pantograph devices are plagued by excessive vibration, which distorts the features of the facsimiles being rendered.
These problems are particularly acute in the area of precious gem and metal cutting. Typically, these materials are very hard and, therefore, the level of vibration resulting from the cutting process is very high. Since the cost of metals and especially precious gems is high, an exacting quality of work from the machine is required if the facsimiles are to be acceptable to the purchaser. Therefore, any device utilized to cut the gemstone and metal figures must be able to duplicate the features of the larger model with the utmost of precision. Yet, the use of bulky, expensive machines to absorb the vibration is undesirable. Clearly, a lightweight, inexpensive device which has a large work area and does high quality intricate work would have considerable practical advantage over present three-dimensional pantograph designs.
The difficulty lies in designing a device in which the cutting shaft and guide shaft are maneuverable through a complete range of positions and angles, yet are sufficiently stable so as to prevent the vibration inherent in the cutting process from distorting the accuracy of the replica. In particular, three-dimensional pantographs are heavy and are typically designed so that the guide and cutting shafts are always vertically oriented. This means that an undercut, a groove or cavity cannot be cut in a blank if material overhanging the cavity is not to be cut away. In order for a pantograph to cut such a groove or cavity, the model and facsimile ordinarily must be realigned, if possible, so that no material which is to become part of the facsimile overhangs the cavity.
Although some pantograph designs provide for limited angular movement of the guide and cutting shafts which allows the overhanging material to be undercut to some extent, no suitable design exists which permits the guide and cutting shafts to be easily maneuvered through a wide range of angular movement.