Venus de Milo sculpture
CNC rotation axis machining the head of Venus de MiloThis project is a fine example of Reverse Engineering: capture an already existing physical 3D geometry and convert that into a 3D CAD model. This is of course the exact reverse of 'normal' engineering (which goes from CAD model to physical product), hence the name Reverse Engineering. Subject is one of the most famous statues in the world: the Goddess of Love, created in marble by an anonymous Greek sculptor. It is called the 'Venus de Milo', and can be found in the Louvre Museum in Paris. In this project only the lady's head has been reproduced in foam, resulting in a small foam Venus bust.
DeskProto screenshot showing the polygon data exported by the Minolta software
To capture the existing geometry a 3D scanner is needed, and for this project the easy to use Minolta Vivid scanner has been used. Any 3D scanner produces point cloud information (XYZ coordinates for many scanned points in space), and the Minolta software is able to convert this point cloud to polygon data (triangles) and export that as DXF. It can also combine scans from several sides to one 3D CAD model.
The resulting DXF file of the head contained 68000 points and 136000 facets; file-size 18 Mb. We were allowed to use it as courtesy of Minolta USA: thanks !
This geometry is used in Lesson 3 of the DeskProto Tutorial, to teach you about Rotation axis machining. As you will need the geometry to replay this lesson, the Venus STL-file has been made available as a free download !
DeskProto window showing part of the toolpaths, for a CNC milling machine with rotation axis.
This geometry is perfectly suited to be machined using a rotation axis. This is a fourth axis that can be added as an extra option to many CNC milling machines. It looks like a 'barbecue axis', and is officially called A-axis. DeskProto supports the use of an A-axis from Version 3.0.
The DeskProto picture draws the toolpaths going completely round the geometry; in reality the tool remains on top, and the complete model will slowly rotate during machining.
The actual machining, using the rotation axis. The picture shows the roughing stage, second layer.
After the roughing operation shown above it is of course possible to add one or more finishing operations using a smaller tool, for the small details. The material block has been fixtured on two sides, where some manual finishing will be needed. The important parts of the head however have been completely machined: in spite of the many undercuts in the geometry, the rotation axis made it possible to reach all details without repositioning the block of material !
The resulting statue. In this case a miniature statue in foam; using a larger machine larger sizes are possible, and other materials as well (even marble).
Below two pictures are shown from a later project: these two children also have been scanned using a Minolta scanner, and next machined in wood. Scanning was more difficult now, as children are less apt (anyway less than a marble statue) to sit perfectly still during the scan.
A small bust being machined in mahogany, and the resulting busts of a brother and sister.
For milling in wood (here mahogany) it is advised to use special cutters for wood. Standard cutters are meant for steel. These may become very hot in wood (more elastic material), even to a state of making the wood black by burning it.