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How to CNC machine a giant sculpture

Creating a giant interactive sculpture: the Doetinchem D-Tower

This project stands out in the DeskProto gallery, first of all because it's size. The D-Tower is a 12 meter high sculpture, so one would not expect such object in the Gallery of a Desktop Prototyping system. However, as DeskProto just works with numbers and does not care whether these are millimeters or kilometers, the software can handle any size.
Only the machine matters. In this project indeed a large machine was used: the Dynamight machine of DeskProto user Komplot Mechanics in Rotterdam. This machine's working area is 5.4 x 2 x 1 meters !

Tower in CAD
Tower assembly scheme
The CAD design, and the assembly scheme of the 19 parts.

The D-Tower is part of a Tower project in the Dutch town Doetinchem. It is the first of total 5 artistic towers (A, B, C, D, E), to be placed on the locations of the city's five former gates.
This first tower is a creation of the artist Q.S. Serafijn and the architect Lars Spuybroek. These two creators have teamed up, as the organic building style used by Spuybroek matched well with the ideas of Serafijn.

Tower part in DeskProto
The milling machine
DeskProto toolpaths for one building block, to be machined on the Dynamight milling machine.

Basis of the artistic concept is an internet-based system that somehow "measures" the emotions of the town's inhabitants. The Tower itself is a means to show the day's dominant emotion to the outside world, using colors. The geometry of the Tower is created as a large beating human heart, using CAD technology to define the freeformed surfaces.

Mould, built of blocks
Mould with part
Each mold is built using blocks; the part is formed by laminating the mold.

Having created this geometry, the challenge was of course how to transform this CAD data into a tangible 12 meters high sculpture. This challenge was accepted by Dutch designers VisionMachine, an 'office for architecture and human space'. They cooperated with two partners: Komplot Mechanics in Rotterdam for the CNC machining of the moulds, and Radius Design in Etten-Leur for the lamination of the Tower's parts. 19 different parts had to be created, of course matching in order to make assembly possible.

Removing the mold
One of the 19 parts
Removing the blocks one by one, resulting in a part of almost 3 meters high.

Komplot Mechanics had to create 19 different large molds (up to 3 meters per mold), and decided to construct these using building blocks sized 125 x 40 cm each.
In DeskProto part segmentation was used to machine these building blocks one by one, in cheap (expanded) polystyrene insulation foam. Each mold was built by grouping series of blocks, and wrapping thin packaging plastic foil around.

Connecting the parts
FEM analysis of the Tower
Connecting the parts by glueing the rims - A thorough FEM analysis for strength has been done.

Next each part has been manufactured by Radius Design using lamination: applying epoxy material and glass fiber reinforcements to a thickness of about 4 mm.
The 19 parts have been connected by gluing the connection rims, reinforced by bolts where needed. Two separate large parts were made to be connected on-site, in order to make transportation possible.

Transport to contruction site
The construction site
Transport by truck, followed by installation of the D-Tower.

It will be clear that the installation of this tower was a major job, requiring a solid foundation and some skilled crane drivers. In order to show the emotions (see below) powerful LED units in RGB colors are built in. The total weight of the Tower is 3000 kg.

Tower in green, by night
Tower in purple, by night
The D-Tower in function: the green tower showing hate, and the purple tower showing happiness.

As mentioned above, the D-Tower is an interactive art project, as the City's inhabitants can decide which color the tower should have in the following night: red, green, yellow or purple. A day-by-day internet research is done to find the inhabitants emotional status. The day's dominant emotion will decide the color of the tower during the night: Red for Love, Purple for Happiness, Yellow for Fear and Green for Hate.

The current status of the Tower can be seen on the Tower's Webcam. The official Tower website is