Reciprocity MSc Material Practice Material Practice 3 2016
Project Outline Material Practice 3 Parametrically defined timber lamella structure
Circular Economy
Rhino + Grasshopper Workshop
Sem. 2 Tools of the Trade Sem. 2 Material Exigencies
Material and Process Material Practice 3 Final Project
Formfinding and geometry definition
Parametric Modelling
Joint Development
Fabric Cover Lamella design and fabrication Joint hardware and process
Special parts and final design
CNC Production
Assembly
Spatial and design intention
Stemming from courses and workshops from semester 2, the aim of the final project is to integrate the work of the whole year into a project that requires comfortably approaching a material and/or set of materials and processes and investigate its possibilities through experimentation.
Recap: Semester 2 - Tools of the Trade
Photo credit: Kevin Cheng
Photo credit: Mathew Venn
“Nothing should be made by man's labour which is not worth making; or which must be made by labour degrading to the makers.” William Morris Tools of the Trade is an invitation to reflect through action on the current landscape of the conceiving and making of things, on the dialogue between the oldest and latest techniques, the relationship between digital and craft. It is about what now is and what is not different in the ways objects and processes are imagined, designed, detailed, represented, communicated, translated into languages that make their realization possible, and how this coming to being occurs. The development and massification of computer aided design and manufacturing (CAD and CAM) during the last decades of last century and the beginning of the present one has had a profound effect in many industries. In particular, digital additive manufacturing or 3D printing and CNC milling, in their widespread popularization and cost reduction over the last decade, have been hailed as a “third industrial revolution” because of the implicit possibility they offer of a dramatic shift in the production and supply chain paradygms according to which the making of things could be decentralized from large industrial facilities and atomized into the consumers’ homes, who would in turn become ‘prosumers’ in their double role of producers and consumers. Besides the real likelyhood or otherwise of such a future, the ‘Maker Movement’ is a reality and interesting collaborative phenomena are taking place in the world of designing and making with different levels of involvment of digital tools. The Ludd-like fear of productive technologic developments representing a threat to traditional crafts and the death of the maker-are not new and similar catastrophist theories have proved to be overly simplistic before. More often than not, a technologic disruptive innovation that presents evident advantages is quickly assimilated into a complex productive ecosystem, where it can take a predominant place in some cases, but it rarely pushes any other alternative to extintion. The preferred way of making things varies greatly throughout the different scales of production, and different technologies and processes make sense or otherwise in relation to the size of the batch to be produced. In this line, the popularization of the said 3D printing and CNC milling technologies can precisely greatly benefit small scale, craft-based designer-makers that can incorporate, with low investment, a way of overcoming limitations or reaching new levels with their produce and evolve in their craft.
Photo credit: fabulalignarius.wordpress.com
Recap: Semester 2 - Tools of the Trade
Digital formfinding and joinery in reciprocal structures “The principle of reciprocity is based on the use of load-bearing elements which, supporting one another along their spans and never at the extremities, compose a spatial configuration with no clear structural hierarchy.” Pugnale A. & Sassone M., 2014 Reciprocal frame structures have been in use for centuries or, in their most general conception, millenia, to overcome the length limit of the structural members available. Recent form-finding techniques have reignited the interest in complex spatial reciprocal frames due to the now manageable ways of digitally describing their geometry, difficult with regular plans and sections. Another problem made manageable through digital means is the structural modelling and analysis of possible complex reciprocal arrangement of structural elements, in which each will be supported at different points and receive loads on different places of their short spans. Qingming shanghe tu (detail), by Zhang Zeduan (1085-1145), the earliest known depiction of a reciprocal structure, “Along the River During the Quinming Festival” is a scroll depicting a popular festival during the Song Dinasty in China.
Several studies on reciprocal frame patterns by Leonardo Da Vinci, Codex Madrid I (1490-1499). The studies focus on the generalization of the geometric arrays for larger applications than the medieval references he could have been familiar with, like the one illustrated by Villard de Honnecourt.
Earliest known western depiction of a reciprocal structure in one of Villard de Honnecourt parchments from circa 1230, “Solution pour fabriquer un plancher quand on n’a pas de pièces de bois assez longs”, or “Solution to build a floor when we don’t have long enough timber”.
Bridge design, also by Leonardo, illustrating a spatial arrangement similar to the solution in Quinming, another practical application for reciprocal structures proposed in the Codex Madrid.
The first account of a reciprocal frame structure to be structurally calculated and verified comes from the work of John Wallis on the 17th century at the University of Oxford: “in 1695, in his Opera Mathematica, John Wallis (Savilian Professor of Geometry at the University of Oxford) published an analysis of the forces in a reciprocal grillage structure. The structure itself was an extended version of a famous design attributed to Serlio, but first sketched much earlier by Villard de Honnecourt. The extended structure was also sketched by Leonardo Da Vinci . Wallis’ analysis is remarkable for the fact that he systematically (and correctly) solved a set of 25 simultaneous equations to obtain the required forces. The main steps in the analysis closely parallel the essential stages in modern finite element analysis, anf Wallis’ calculations can be seen as a key step in the development of structural analysis techniques.” 1 For the course of Tools of the Trade, I intend to focus on the dialogue between the digital design of simple reciprocal structures using parametric software and incorporation of the craft dimension both in the digital craft of modelling and in the transition from digital design to built through making, both by traditional praxes and computer aided manufacturing techniques. Keeping in mind the reason to exist of this kind of structural solution and the broader context in which they would make sense or otherwise, lenght limit is a key input for any development. The Uruguayan timber engineered products industry is flourishing, at present high quality plywood in standard sizes (2440x1220mm) is produced, as well as glue laminated beams made with eucalyptus grandis fast-grouwing, FSC certified wood. 1.“John Wallis and the Numerical Analysis of Structures”, Houlsby, 2014
Lamella Roofs
Porträt des Konstrukteurs und Städtebauers Friedrich Zollinger, 1937/38, Foto: Privatbesitz
Zollinger Lamella roof being built in Merseberg (Open Source) 1922 On November 25th 1924 Hugo Junkers applied for his first patent (No. 459038) for his iron lamella halls. They proved enormously succesful in Germany in between wars.
Image: Buckhard Franke
Patent file drawings for patent nº 462881, an improvement over Junkers’ first patent.
Lamella Roofs are a particular case of a 4-way reciprocal frame structure in which 2 linear elements rest on the middle point of a third, all members being the same. They were devised by Friedrich Zollinger from 1910 onwards. Zollinger was then Building Comissioner and City Architect of Dessau, Germany, and faced with the challenge of providing housing solutions for an increasing population within a tight city budget. Publicly funded new buildings was prohibitive, thus Zollinger took the approach of focusing in the extension of existing buildings. In most cases foundations were inadequate to support the constuction of an additional level in masonry, and to complete the challenge, the roof construction of typical houses consisted of high pitched trusses with structural elements on the section that blocked any possibility of generating a livable attic space. Zollinger’s solution was a structural system to substitute this roof construction allowing for a clear loft space using the same building outline and with inexpensive, readily available materials, mainly wood planks and simple hardware. Its ingeniousness lies at its ability to respond to constraints with a conceptual hybrid between a laminar and reticular structural model. Its main weakness was the lack of rigidity of the joint, solved by the sheathing planks acting as a diaphragm, but this was the issue most improvements that have picked up on the system have focused their attention, since it is wherethe main room for refinement and thus for material efficiency improvement remains.
Archiv Bernd Junkers - Junkers’ prefabricated, lightweight lamellae could be shipped, flown or even taken on the back of donkeys if necessary, anywhere in the world, to allow easy for deployment of hangars in the explosive expansion of the aviation era in the 1930s that Junkers, aeronautic engineer, pioneered himself.
Recent precedents
Reciprocal Frame Structures Made Easy Peng Song 1 Chi-Wing Fu 1 Prashant Goswami Jianmin Zheng Niloy J. Mitra Nanyang Technological University, Singapore University College London
Daniel Cohen-Or Tel Aviv University
An interest in the digital description of geometrically complex reciprocal structures can be identified in the research carried out by Peng Song, Chi-Wing Fu et al. in the paper of which the first page is reproduced and can be found complete here: http://vecg.cs.ucl.ac.uk/Projects/SmartGeometry/reciprocal_frame/paper_docs/reciFrame_sigg13_small.pdf in which they describe the creation of a software algorithm to generate different arrays of reciprocal frame structures given a particular surface. Another good resource and example of approach to systematizing scattered information and organizing it to break down the problem is the paper by Danz depicted below. Found at: http://dmg.be.washington.edu/reports/Reciprocal%20Frames%20(Danz,%202014).pdf
Figure 1: A large reciprocal frame (RF) structure designed by our method; there are no central supports as rods rest on and are supported by adjacent rods reciprocally. When constructed, rods are usually tied or nailed, as shown on the left, in a physical model that we built.
1 Introduction
Abstract A reciprocal frame (RF) is a self-supported three-dimensional structure made up of three or more sloping rods, which form a closed circuit, namely an RF-unit. Large RF-structures built as complex grillages of one or a few similar RF-units have an intrinsic beauty derived from their inherent self-similar and highly symmetric patterns. Designing RF-structures that span over large domains is an intricate and complex task. In this paper, we present an interactive computational tool for designing RF-structures over a 3D guiding surface, focusing on the aesthetic aspect of the design.
The reciprocal frame (RF) is a three-dimensional assembly structure made up of three or more sloping rods in a closed circuit, namely an RF-unit (see Figure 2 (left)). The inner end of each rod rests on and is supported by its adjacent rod. Signified by the word “reciprocal,” which expresses mutual action or relationship, such closed circuit is obtained as the last rod is placed over the first one in a mutually-supporting manner. At the outer end, the rods are given an external support by a wall, ring beams, or columns.
The fundamental concept of reciprocal frames [Chilton 1995; Larsen 2008], has been known for many centuries. One classical example is the various architectural designs by Leonardo Da Vinci There are three key contributions in this work. First, we draw an analogy between RF-structures and plane tiling with regular poly- during the Renaissance. However, it was only until the very recent gons, and develop a computational scheme to generate coherent decades that this topic caught the attention of architects and structural engineers, because of the emerging applications of computaRF-tessellations from simple grammar rules. Second, we employ a tional optimization and CAD tools to enhance, enrich, and scale up conformal mapping to lift the 2D tessellation over a 3D guiding surthe construction [Pugnale et al. 2011]. face, allowing a real-time preview and efficient exploration of wide ranges of RF design parameters. Third, we devise an optimization The reciprocal frames are fascinating. Starting with only very simmethod to guarantee the collinearity of contact joints along each ple material in the form of rods, one can build a complex grillage rod, while preserving the geometric properties of the RF-structure. structure made of one or a few similar RF-units (see Figure 1), Our tool not only supports the design of wide variety of RF pattern by iteratively putting RF-units around one another [Bertin 2001]. classes and their variations, but also allows preview and refinement No central supports are required in the resulting RF-structures, and through interactive controls. one can also disassemble and re-assemble these structures, facilitating their transportation from place to place. This makes RF a highly cost-effective deployable system, particularly suitable for CR Categories: I.3.5 [Computational Geometry and Object Modrapid constructions of temporary structures [Larsen 2008]. eling]: Curve, surface, solid, and object representations; Keywords: Reciprocal frame, computational design Links: 1 joint
DL
first authors
W EB
V IDEO
Apart from the technical aspects, the reciprocal frames also have their intrinsic beauty. Similar to bird nests in the nature, which are built from discrete simple elements, the reciprocal frames share a common characteristic of being a modular structure composed with simple rods. These rods nicely form self-similar and highly symmetric patterns, capable of creating a vast architectural space as a narrative and aesthetic expression of the building.
Reciprocal Frames, Nexorades and Lamellae: An investigation into mutually supporting structural forms
Calder Danz, MS.dc candidate, Design Machine Group, University of Washington Prof. Brian R. Johnson, Advising 12/08/2014 Abstract:
Figure 2: Left: A three rods reciprocal frame, as an RF-unit. Right: a large RF-structure made up of tied rods.
This paper presents an overview of the current body of literature available on reciprocal frame structures, the history of the RF as an architectural typology, and a discussion of the links and disconnects between research and practice in this area. This information is synthesized by organizing the different morphologies observed into a set of heirarchical lineages or ‘phylogenies’ based on their historical context and the technological requirements for their rationalization processes.
1
Plywood Uruguay Projected wood supply destined for mechanical processing
Industrial installed capacity: Weyerhaeuser Productos S.A. Present in the country since 1996 manages 125.000 of own land and buys from other growers. Produces exclusively plywood in Uruuguay (Present in over 10 other countries). In-house nursery next to the factory can produce 3.000.000 trees a year. Processes both eucalyptus and pine making different kinds of plywood according to content and quality of each. Processes 550.000 m3 of raw roundwood a year. 90% of production is exported.
Mederos is a Uruguayan company that manufactures CNC milling machines in the country using imported and domestic parts. They develop the electronics, hardware and firmware and provide support for their products. Full size CNC milling machine prices start at around ÂŁ 9000.-
(thousands of m3) Uruguay XXI institute
8.000
7.000
Eucaliptus
6.000
Pine
5.000
4.000 3.000 2.000 1.000
1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 2018 2020 2022 2024 2026 2028 2030
0
Images courtesy of Weyerhaeuser Productos S.A.
Unto This Last www.untothislast.co.uk Case discussed on semester 2 All high-quality plywood furniture Extensive catalogue - No Stock (So no storage). Everything predesigned but made to order. They only store a reasonable amount of plywood and produce to order in a centrally located London workshop, which allows them not to invest heavily in storage or idele stock, as well as minimizing transport costs and associated carbon emisions. By locating the production close to the intended destination market, the flow of materials is streamlined and the design, which consists of data, an immaterial asset that can be effortlessly transferred anywhere the company needs to expand. An interesting concept that could be extrapolated to a larger scale for the built environment where the production means are versatile and available at a reasonable distance to make transport acceptable in finantial and environmental cost, and the design can be distributed digitally ready to make and assemble.
The engineered timber products industry in Uruguay has been developing in the last two decades as timber has been becoming incresingly available as a result of a Forestry Law passed in 1987. There are 2 major paper pulp mills in the country, a project for a third one, as well as two major industrial facilities where timber is mechanically processed. One of these mechanical processing plants specializes in solid sawn eucaliptus grandis with which they make fingerjointed panels as well as glue-laminated beams. The other large industrial facility belongs to American company Weyerhaeuser, they manufacture plywood panels of different mixes of pine and eucalyptus veneers. All these products are intended for the American, Asian and European markets, therefore they comply with required standards and are structurally and environmentally sound. Computer Aided Manufacturing in the form of flatbed CNC milling requires dimensional consistency, plywood meets this demand and eventually larger solid glulam or CLT elements could be routed on larger milling beds. Plywood, therefore, proves a good starting point as a local research of which to investigate the potential with the Uruguayan context in mind, keeping the possibility open to extend research to other wood based products. Plywood is of dependable thickness and its layering helps reduce its natural anisotropy, which makes it suitable for CNC processing and has predictable mechanical properties. The promising field of construction using mass timber panels appears as a possible future market destination for the abundance of timber supply projected for the next few years and decades.
Project for multi-family residential development 2014, Arboreal Architecture Images by authors.
Recap: Semester 2 - Circular Economy
Souce: INSPIRE institute
The flow of materials in a linear economy is wasteful, both in the materials that need to be sourced and become unavailable after the life cycle of the products they form ends, and in the energy required to extract and isolate them, move and transform them, and dispose of them safely. A circular economy is a concept that aims at eliminating the very idea of a life cycle end, seeing prod ucts rather as a temporary depository of resources than as an "end" product in itself, with no other destiny than end up either in the atmosphere as harmful to humans and climate carbon compounds after burning, or buried in a landfill, waiting for centuries or millennia to break down and become available again to the biosphere as different compounds. A cycle conceived as a circular economy separates materials in two kinds, those that can return safely and even beneficially to the biosphere as nutrients by biodegrading, and those that can return to industry as resources for production. The design strategies in a circular economy conceive the flow of materials in all forms as a system, and it is the system that needs to be designed and engineered rather than only individual products, buildings or components. In a system so conceived, different groups of materials should be designed for easy, low-energy disassembly. A path towards a circular economy implies rethinking everything, and as challenging as it may seem, it has been done before and it is within our power as a species. The first industrial revolution was made at a huge environmental and social cost, but there was and is good in it. A circular econ omy strategy seeks to potentiate that what is good about human industriousness while revolutioniz ing again the whole productive system to not only apply minor corrections to delay an inevitable collapse, but rather revert the noxious ways in which we operate within the broader ecosystems as we learn how to work within them. For the purposes of Material Practice 3 we will incorporate Circular Economy guidelines and aim for designs that keep materials easy to separate and sort out into biological or technical cycles.
Souce: Ellen McArthur Foundation
Project Development
Circular Economy
Design for disassembly Consciously chosen materials Biological cycle materials separate from Industrial cycle materials
Rhino + Grasshopper Workshop
Sem. 2 Tools of the Trade Sem. 2 Material Exigencies
... Parametrcially defined geometry that can be adapted to sizes of elements available and other possible constraints and that can be precisely produced with reasonably available technical means for the Uruguayaan context
Outdoor area assigned
KÄNOPII
x 200 x 12 x 23 x 13 x 11 x 500 x 500 x 250 x2 x2 x2 x1
Form development Considering the timscale available and the scope of the excercise, an initial idea of attempting a parametric double curvature lamella surface was rationalized to using the opportunity to learn from the material ponit of view and the resolution of a built result rather than dedicating most of the time to the geometric resolution without guarantee of arriving to a buildable alternative by the end of the available time. The proposal is for a single curvature section of a cylinder shape that allows for a reciprocal frame configuration comprised of almost all identical lamellae (except for the ones solving the edges) and using the generative lines of the lamella lattice as edges. This creates a simple, slender canopy shape that was designed to be site-specific but also as a generic enough solution so that it can be thought of as a case study for a replicable, open system that could accept many different alternative solutions regarding connection to support points, type of cover, materials used or scale.
A first attempt of generating a barrel vault geometry that would keep all lamellas identical was done in Rhino and Grasshopper using a definition by Aleksandr Barilov (http://www.grasshopper3d.com/profile/AleksandrAlexBarilov) that creates the linear geometry and the individual extruded rectangular lamellas, but generates connection points where the ends of 4 lamellas meet, which is inconstent with the intended Zollinger interlocking design of a 4-way reciprocal frame. It would have been possible to edit this definition to adapt to the configuration desired, a future development of the project with a different timescale could allow for deeeper scope and the parametrical resolution of all the geometry and components.
Parametric geometry generation
Grasshopper algorithm developed by Dr. Cristina Nan to generate the reciprocal frame geometry on barrel vault surface. The geometric pattern generated was baked from grasshopper to obtain base lines on which the extruded CAD drawn lamellae were alligned.
The geometry of the lamellae was developed in CAD software to allow for quick alterations after the input data from the overall geometry is taken in consideration and to prepare files to CNC mill. Future development of he parametric definition could incorporate all these stages into one parametric definition.
Form development - experimentation across different scales
Connections - joint development
The initial designs tested stemmed from studying an alternative connection to the standard solution used by Zollinger to join boards with their ends cut to the appropiate angle with a pin across them (See detail in page 5) which results in its main weakness regarding lateral stability. The intention was to devise a solution in which the ends of two lamellae would rest on the top part of the middle of a third one. This created a necessity for a way of holding the two ends linked by two bolts with another still-to-be-devised mechanical fixing to the third lamella. This quickly implied a reduction in efificiency since more components are needed and no improvement in the rigidity is achieved in comparison to the original Zollinger system. It became a goal that the joint should be resolved with only one mechanical fixing element.
Keeping the idea of mechanichally bolting across the two meeting lamellae and also going with each of them through the thickness of the third one, an angled mortise and tenon-like connection was devised that uses the thickness of the lamella, together with the width of the mortise, to generate the designed geometry by locking at the desired angle. This lock can be tightened by only one bolt going through, thus generating the effective friction in the timber-to-timber part of the joint. This design owes a lot to the original Zollinger solution and only improves the rigidity of the joint by virtue of the timber connection that, to achieve this rigidity, relies on extremely accurate means of manufacture (CNC milling) and engineered timber products that are dependable in their behaviour , two things Zollinger did not have.
The joint was tested with the hardware and a full scale lamella was cut out of the actual birch plywood to be used to get a sense of the rigidity of the material in such proportions. A lower ‘step’ under the tenon that forms at the end of each lamella resulted problematic for assembly and also conceptually redundant so it was eliminated and a more fluid undercurve of the lamella was designed to provide a material path where is needed for the loads. It also resonates with the technology used in production since, the less sharp angles, the quicker and more fluid the cutting with the CNC results. This shape could also be parametrized to be responsive to the position and conditions of each lamella in an irregular pattern generated by a parametric deifinition that creates double curvature surfaces or pure compression vaults.
Connections Connections between lamellas were prototyped and tested on the actual birch plywood to be used, with very good rigidity in the connection and excellent dimensional stability of the cut pieces. From the first version cut using the CNC it was necessary to slightly increase the diameter of the holes on the ends of the lamellas and the thickness of the groove in the middle to provide for a more agile assembly without compromising the stiffness of the timber to timber part of the connection that remains as tight as practically possible. This is key to the operation that is going to be repeated the most times on assembly and as such the one that should be optimized in terms of the amount of time it should take to position and secure each connection. The simplicity of the self-setting-out angle between the mortises and tenons due to their geometry makes putting together each joint very straight-forward and an overall agile process. There is only one 100 mm section of M6 threaded bar, 2 nuts and 2 bolts to create each connection. The connections do not provide the required lateral stability and horizontal stiffeners every two rows weill be used. This can be in the form of flat steel braces runnin the length of the structure from end to end. These would also provide the attachment points for the fabric cover in horizontal overlaping strips.
The connection of the structure on the straight support lines at either end (Here shown meeting with CLT footing) was devised considering several conditioning issues such as the need for a very quick and easy to assemble and dissasemble system, the desire of, when possible, solve it with simple, readily available off the shelf components and the possibility of dimensional adjustment on site as well as ease in the setting out. End lamellas were designed with a large hole near the thick end, through which a 10mm threaded rod goes through, and also through a precut piece of metal tube that provides the correct spacing and support and fixation brackets. A marking jig with the spaces between brackets can be prepared and broough to site or the CLT pieces could already come with the brackets already attached from the workshop.
Structural model and analysis
1 - Bending moment diagram
A linear elastic analysis of the structure using SAP2000 was done by Dr. Bernardino D’Amico from Edinburgh Napier University, a collaboration made possible by Prof. Abdy Kermani. The analysis is of “the strength and displacement of the structural members, i.e. no verifications have been made in terms of overall stability, buckling or strength of the connections.”
The following assumptions were made and input values were assumed: • • • •
The structure is assumed to be supported by pinned joints (see Figure 1). The internal connections between each member are modelled as fully fixed. Considering the fact that the structure will be on for a very short amount of time, a uniformly distributed load of only 200 N/mm2 has been considered. Material and cross-section properties for the plywood members were set as follow: Elastic modulus, E = 10000 N/mm2 Cross-sectional width, b = 18 mm Cross-sectional height, h = 98 mm Height of cross-section at the ends of the member, he = 25 mm
Bending strength verification: In figure 2 is shown the distribution of bending moments around the members’ strong axis. The maximum bending moment, , within the structure has been found to be ≈ 250000 Nmm. The corresponding maximum bending stress,
,
Where:
Hence:
2 - Undeformed shape
3- Deformed shape (magnification factor: 50)
,
=
is equal to:
=
ℎ2 18 ∙ 952 = = 27075 mm2 6 2
,
=
250000 = 9.2 N/mm2 27075
The bending strength of 18 mm wide plywood is about 40 N/mm2, i.e.
,
< 40 therefore OK!
Shear strength verification: The maximum shear reaction,
, within the structure has been found to be about 350 N.
The corresponding maximum shear stress, =
3 2 ℎ
,
=
is equal to:
3 ∙ 350 = 1.16 N/mm2 2 ∙ 18 ∙ 25
The shear strength of 18 mm wide plywood is about 9.5 N/mm2, i.e. Discussion
< 9.5 therefore OK!
The mode of deformation of the gridshell can be seen in Figure 1: being shaped essentially as a barrel vault, the gridshell bends out of its plane, with maximum values as shown in Figure 2. The vertical displacement of the top side of the gridshell is about 6 mm (on average).
CNC milling 2D Drawings of the pieces in the sheet they will be cut from, from CAD to Vcarve, a specific software for use with the CNC milling machine.Parameters such as bit kind and diameter, cutting depth andnumber of passes are selected. Software can run simulation of cutting outcome in 3D (showm) and calculate time it takes to cut each plywood sheet. Vcarve translates the vectorial information to a â&#x20AC;&#x153;toolpathâ&#x20AC;? file that describes the movement of the milling head in three axes. Initially 8 lamellae were made to test the shape and process, to then mill the final design.
CNC milling Milling each sheet takes approximately 1:30 hours. Tabs were added in VCarve, these are short sections that are not fully cut in the vector path, so as to hold the piece when the bit completes the cut. This avoids the cut piece from moving after becoming loose from the rest of the material, which could cause it to move and be altered unintentionally by the rotating bit. These tabs can be easily and cleanly cut wit a small backsaw. The “hairy” edge seen in the pictures was caused by cutting one sheet with a damaged bit that was then replaced, obtaining a cleaner cut after that. In any case all pieces need some sanding to clean the edges, only that with these particular batch (21 pieces) the finishing was more time-consuming. Bottom right photograph shows a “before and after” of the finishing. Videos of the milling and more photographs can be found at: http://adieste.tumblr.com/
Joint testing A section of the structure was built using the first set of 8 lamellae cut with the CNC milling machine. The joint was tight and solid, and the resulting structure worked very well and provided sufficient stiffness for a person to stand on without excessive movement. The tightness allowed by the high precision milling is key to this joint stiffness since the main locking is in the timber-to-timber connection. The holes for the threaded bars to go through were found to be excessively tight and this is not a neccessity, hence the diameter was increased to 7mm since the threaded bar to be used is an M6. This proved with the first pieces made aftet the adjustment to highly decrease the time needed to put together each joint.
Fabric attachment A first alternative for the attachment of the fabric was carried out by placing closed hooks on the face of the edge lamella, through which a wire rope was to be threaded while also going through a fold along the edge of the fabric sewn up to allow for it. Holes in the fabric where the closed hooks have to go through can be cut out in place with the structure up so as to allow for precise placement. A different solution attempted uses the protruding ends of the half lamellae that rest on edge lamellae to wrap the fabric around them. In the design as per that moment, this implied too long spans in the fabric which made it difficult to avoid wrinkling, so, considering we had ta free mortise in each edge lamella, since only one lamella ends on each end one, a â&#x20AC;&#x2DC;stumpâ&#x20AC;&#x2122; piece was designed to allow for an intermediate support for the fabric. In this solution the attachment of the fabric to the structure is made byinserting eyelets on the fabric edge where a screwand washer can be placed and fixed to the bottom edge of the edge lamellas and stumps.
Special parts In addition to the generic lamella, less numerous half lamellae, both with two and one end socket to receive either one or two other lamellae were made to solve the edge condition and the attachment of the canopy to the CLT footing. Also stump pieces were made to provide better support for the fabric cover on the edge of the canopy.
Discussion
Photographs courtesy of Shaper
The result of the projectâ&#x20AC;&#x2122;s evolution was validated technically and at a prototype level. Additional lessons are expected from the actual assembly of the structure at the Univeristy and then its dissasembly and reassembly in London. Input from that experience can be incorporated into future iterations of the design and further refinement of the system. Other materials could be tested in similar arrays, most evidently steel with light gauge, cold formed components such as Junkerâ&#x20AC;&#x2122;s system, but from a material point of view, the global consideration of the project within Circular Economy and Tools of the Trade proposals as an ethos it made sense to focus on a readily available timber engineered product such as plywood. Future development of the project that could be of interest, as noted throughout the report resides in the possibility of refining the parametric definition of the geometry of the structure. This could be done in two interdependent and interconstraining lines, being the general form-finding algorithm and the accurate generation of the geometry of each lamella and joint. Such a definition could be made to generate double curvature surfaces that follow compression paths, responsive to load condition and a myriad of other variables. The complexity of the joinery remains a challenge in this area and would imply angle constraints that represent limits in the concavity of the surface, as well as delicate points to look at regarding operability of tools in the clear spaces that result of such algorithms. Within the Uruguayan context opportunities definitely can be identified for development of low-cost structures that make use of a local and sustainable resource. The key issue to allow for these opportunities to materialize is creating open systems and ways of making that can evolve and respond to availability of different resources in different conditions, but have clear guiding principles to make judegments regarding the apropriateness of technology, material and process in these diverse situations.
Discussion - emerging Recent products have been aiming to combine the capabilities of a CNC milling machine and a handheld router; and, more recently, augmented reality. From the comparatively rudimentary Handibot released by the CNC manufacturer Shopbot (www.handibot.com) to the just released Origin by Shaper (www.shapertools.com), the efforts have been aimed at reducing the scale of the tool needed for precision milling, thus increasing its portablility. The main breakthrough of the Origin is its augmented reality capability, that scans a special tape to be placed on the material to cut in order to map it and locat itself in relation to the x and y axes of the sheet material. The user loads the file on the tool and roughly guides the milling head, which self-alignes to the correct path to cut and corrects the movement to provide a precise cut. These tools are also cheaper than flatbed CNCs and can be thought of as an alternative that can maeke sense in the technical context considered. They could also be used on-site to create special pieces or new and altogether different parts needed that could come up, or make quick adaptions and modifications as required, and, its main advantage, completely breaks free from dimensional constraints, so potentially this technology could be used for domestic DIY uses to construction applications like precisely milling CLT panels according to Building Information Modelling (BIM) files that can be transferred and updated seamlessly, so we could shift from a paradyigm of large, static milling centers to mobile, inexpensive alternatives that will likely become more reliable, versatile and cheap. From a material point of view, the suitability of timber engineered products to be precisely shaped and remain dimensionally stable makes the combination of timber engineered products and digitally controlled milling a powerful one, that doesnâ&#x20AC;&#x2122;t necessarily need to be constrained to 3 axes milling. Photographs courtesy of Shaper
Photo: William Langford
Photograph courtesy of Shopbot
William Langford, student at FabCentral, a digital fabrication facility managed by MIT's Center for Bits and Atoms, developed in 2012 a low-cost 5-axis desktop CNC machine that can replicate most of the pieces required to create a copy of itself or indeed variations or any other part, not unlike 3D printing.
A possible application imagined for structures such as the one proposed is for open crops protection or fully closed greenhouses of different scales and materials such as gluelam lamellae.
Acknowledgments Many thanks to all involved with exceptional good will and that in one way or another cotributed to the development od this project: Course Directors Dr. Cristina Nan Malcom Cruickshank Catriona Gilbert Richard Collins Prof. Adam Stokes Dr. Tom Barraclough Santiago Vera Lewis Lilburn Katerina Alkiviadou