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How to CNC machine jewelry wax models

CAD/CAM process to create a ring with GemVision Matrix

Jewelry design and manufacturing is a very good application for DeskProto, as CNC machining can very well be combined with the 'traditional' manufacturing processes. This project concerns one of the first rings that was made using DeskProto, back in 2001.

Since many centuries gold and silver ornaments are manufactured using investment casting (the "lost-wax method"): first a model is created in wax, which is converted into a plaster mold by casting the plaster around and then melting the wax out of the cavity. The gold or silver is cast in the plaster mold, and afterwards finished by (hand) polishing. This method can very well be applied in a small jewelers's workshop. Traditionally speaking the original wax models are carved by hand from a sketched design, nowadays most designs are created using CAD/CAM technology. Two alternative processes are available to create a wax model based on a 3D CAD design: CNC machining and 3D Printing. This page describes the CNC milling process.

The ring design in Matrix
Calculating toolpsths in DeskProto
The CAD-Design in DG Matrix, and the CNC toolpath in DeskProto.

GemVision Corp. in Davenport (Iowa, USA) is a supplier of new technologies for the Jewelry industry, one of them being a complete CAD-based design software package called Digital Goldsmith.
The silver ring shown here has been designed using the Digital Goldsmith Matrix software (based on the Rhino CAD engine). This special jewelry orientated CAD software combines very well with the DeskProto CAM software; a desktop CNC milling machine makes it possible for any jeweler to quickly create the wax models needed for manufacturing of the design. The designs are transferred to DeskProto using STL files.

CNC milling: roughing
CNC milling: finishing
Machining in wax: first roughing and next finishing.

The wax models were machined on a desktop CNC milling machine. A light machine is sufficient for wax models. Important for jewelers is the availability of a fourth axis (an A-axis, or 'barbecue-axis') as this makes it possible to machine rings. The models of this ring were first machined with a ballnose cutter (diameter 3 mm, or 1/8") for a smooth surface finish, and after that with a conical engraving cutter to add (or in fact to remove wax for) the small details.

The wax model
The resulting 'raw' casting
The wax model, fresh from the machine, and the result in silver 'as cast'.

Some final details in the wax model have been finished by hand, for instance a small radius on the inside of the ring (an area that cannot be reached by the cutting tool). After that a mold has been created, and a silver ring has been cast.

After tumble-finishing
The result after finishing
The ring after tumbling, and next the final finished result.

As can be seen in the illustration, the result of the casting is still quite rough. This is standard for this manufacturing technology, as are the procedures needed to refine the result: tumble finishing (which is an automated polishing process inside a rotating drum) and finally hand polishing.

The resulting ring is ready for the client, and completely conforms the digital design that has been approved before manufacturing. What is more, in case the partner of the client wants an 'identical' ring in his/her size this is very easy: just enter a scaling factor in the design software and repeat the manufacturing procedure.