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How to CNC machine a statue in marble

Artist creates perfectly refined human torso sculptures

This project is a DeskProto application in sculpturing art. Dutch artist Eja Siepman van den Berg is famous for the perfectly refined human torso sculptures that she produces in white marble and other materials. As the completely manual production process of these sculptures requires much time, effort and hard labour she has been looking at new technologies to facilitate her work.

The project has been completed in 1997, so when reading you need to realize that 3D scanning technology has made a lot of progress since. The screenshots on this page show DeskProto V1.1

One of the possibilities is using CAD/CAM technology to create the final sculpture in stone, and thus to use an NC machine to perform most of the heavy labour. In this project the geometry again has been manually sculptured, however now in plaster instead of in stone. The plaster sculpture has been digitized using a 3D laser scanner, and the resulting data have been used to create a 3D CAD-model.

DeskProto Screenshor (wireframe)
DeskProto window showing the DXF-file (about 13,000 triangles) as wireframe.

In this project the DeskProto software has been used to import the scan data (a DXF-file containing a polyface mesh), to calculate NC milling paths for a few scale-models in transparent perspex (being very fine sculptures themselves), and finally to create toolpaths for the full-size statue in marble.

CNC toolpaths
DeskProto window showing part of the toolpaths (in order to make them clearly visible a larger path-distance has been used for this illustration).

As the models have been created on a three-axis milling machine, each model has been milled from two sides (front and back), using the base of the 'statue' to fix the model.
The real statue has been CNC machined in pure white Carrara Marble (a full size statue), by Bertozzi Felice Srl in Italy. This has been done on a CNC machine specially designed for milling marble, with a diamond coated cutter and using much water as a coolant. In order to achieve a smooth result a ballnose cutter was used.

Marble milling machine
The statue in marble
The marble milling machine, and the resulting marble statue.

References: the artist is Mrs. Eja Siepman van den Berg (Beetsterzwaag, The Netherlands). The scanning has been performed by 3D Imaging (Antwerp, Belgium), who also performed the conversion from scanned data-points to 3D CAD geometry using the Surfacer (TM) reverse-engineering software.

Pattern for the artist
Handwork in marble
Opposed the traditional method: a pattern model for handwork, and the marble statue in progress.

This method of creating a marble statue by CNC machining is of course new. In the Bertozzi Felice workshop we also saw an example of the traditional method of sculpting: cutting by hand, using a (scaled) original as pattern for 3D measurements with all types of callipers. See the two images above.