top: CNC routed beech, stage one of machining. Stage two, the block of beech is flipped over and machined from the underside. Post-machining, the securing tabs are carefully removed. left: The single piece has been machined and cut free, the offcut material can be seen on the left. Markings from the cutting tool can be seen on the façade. 3D printed components are slotted into place and adapted if required.
all images: richard collins
Critical sections of geometry were thickened. The block was also referenced so that it could be machined from both sides. Machining tabs were included that held the piece together during the automated process and were then cut away using a bandsaw and tenon saw. The sequential series of machining passes created an expected and quite appealing texture. To machine a block of wood in this way is not an efficient use of material; if there were a requirement to make multiples of the form such an approach would be difficult to justify economically. A considerable amount of time, effort and material had been put towards the creation of the CNC routed piece. If the form were left uncut it would have a greater physical presence when experienced directly. However, if the form were sectioned the subdivided pieces could be laser-cut creating the perforations that were so significant to the design. The experience of the perforated subdivision would be especially persuasive when experienced through photography and enlargement. At the time of the competition, photography of the model took priority and the form was divided. By cutting, even with a fine saw, material was removed. If the pieces were to be re-joined, the form would be distorted This led to me trying out a third approach. The third approach involved using the Objet printer, which uses polyjet technology. The stated resolution of the ‘Objet Connex 260’ is 0.03mm. The accuracy is much better than with the Dimension Elite and it is possible to print in a range of materials. However, when printing details smaller than the recommended limits, cleaning away the support material is problematic. The structure of the secondary support material will break down in water, but it does not dissolve, it only delaminates. Problems
can occur because the model material that is used alongside the support is hygroscopic, and when it draws in fluid it becomes weaker. As the structure of the support material breaks down it expands and can cause the weakened model material to break. During the testing phase there were several ruptured walls, the breakage occurring at the stage when the support material was being removed. The more support material there is relative to model material, the higher the chances of breakages. If the support material can be manually scraped off, then delicate structures stand a much better chance of survival. After using a chisel to scrape off the surfaces, a pin was used to prod out support material from the perforations. The support material is a jellylike, soft waxy material that crumbles relatively easily. However it does adhere to the surface of any model material that is supported by it. The surfaces of such supported sections have a matte roughness that contrasts with any unsupported surfaces, which will be much glossier. To remove more support material and improve the surface quality the forms were hand-sanded. After an acceptable smoothness was achieved with a rough grade of sandpaper, the same process was continued with increasingly finer grade sandpaper. When the majority of support material had been removed, a small amount of water was introduced with wet-and-dry sandpaper to ease the action of sanding and aid the removal of debris. Out of the three approaches this was the most successful. However, it was not a complete success as under the heat of the exhibition lighting an extended section started to deform. This challenge was addresses hours before the opening with some materials that came to hand.
From the top: left, Polyjet test piece. A scaffold of ‘support’ surrounds the perforations. Right, testing material palette and levels of transparency. Polyjet printed entire perforated wall, directly after printing on build platform. Left, manually removing support material from delicate perforations. Right, slowly sanding the surfaces to remove unwanted blemishes. The polyjet printed wall slotted over the other 3D printed components and was held above the wooden surfaces.
below: Photographed model, from above and in section.
On Site review 35 : the material culture of architecture
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