UCL Design for Manufacture Portfolio by Sotiris Monachogios

Sotiris Monachogios

Design portfolio Tutors: Vincent Huyghe, Tom Svilans, Emanuel Vercruysse Advisors: Tim Lucas, Peter Scully, Prof. Bob Sheil Programme Directors: Chris Leung, Emmanuel Vercruysse Design for Manufacture MArch The Bartlett School of Architecture, UCL 2018-19

Brief introduction

The booklet you hold in your hands includes the progress of a young architect during the 15 months of studies in Design for Manufacure. It comprises of the ideas, sketches, experiments, tools and prototypes, successes and failures that led the author one or two steps closer to further understand certain processes in the realm of architecture and making. The processes of design, materiality, material durability and, ultimately the omnipresent symbiotic relationship between design and making, were prevalent throughout the course.

The portfolio is focused on the mechanisms and the means by which the author’s interest evolved and was finally captured by the process of active bending: from the first contact with making timber products and further processing them, to the later framing of the field of interest. The experiments with active bending lead to the final artefact, a structure of three birch plywood surfaces interconnected with a network of SLS printed nodes and wooden pegs, creating a wireframe of symbiotic elements all being in an internal fight of forces and yet reachging a geometrical equilibrium.

At the end of the issue is an appendix with a summary of other work done during the past period, which made a less apparent, yet non-negligible contribution to the whole journey until the final design project.

London, November 2019 2

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note: the work presented here is done by the author, unless stated otherwise

Table of contents

A – towards bending active timber

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A.1 Making engineered timber 5 5

A.1.1 Preparation and machining of a CLT panel A.1.2 Manufacturing curved CLT panels 11 A.1.3 The introduction of the core layer 13 A.2 First active bending experiments

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A.3 Segmenting shell to developable strips A.4 Machining and assembling on a jig A.5 Bending active floor segment

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A.6 From single pegs to nodes 33 A.7 Bending active symbiotic surfaces A.8 List of peg details

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B – appendix 50 B.1 Design of a parametric pavilion 51 B.2 Design and fabrication of a vehicle B.3 Robotic milled joints 55

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A t owards bending active timber

A.1 Making engineered timber A.1.1 Preparation and machining of a CLT panel Part of team with: Bedir Bekar

The initial motivations that triggered our investigations had to do with honesty in the global architectural form, moving away from faceted geometries dictated by flat panel assemblies.

The material choise was timber, having the potential to compete with steel and cement, being environmentally friendly and more pleasant for people to inhabitate if treated properly.

CLT or cross laminated timber, stands for the timber composite that comprises of an odd number of layers, starting from three, where the grain direction is alternating between the layers. Glue and pressure applied to the structure while drying is what makes the product strong.

sawing timber beams to required section size

planing sections for gluing

lamination of pieces under time pressure

The lack of homogeneity and wood’s remarkable differences in strength according to the direction of the grain is is counterbalanced by the alternating layering.

Processing of timber sections was a prerequisite for aggregation of parts and decent adhesion of layers.

A three-layered CLT plank of 300x1600x80mm was prepared and was later milled on the robot, using a subtractive logic, making a structurally optimized bench.

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processing timber sections in the planer thicknesser

clamped CLT panel: improvisation because of the lack of hydraulic press

A.1 Making engineered timber A.1.1 Preparation and machining of a CLT panel

The final CLT plank required some further processing to give a finished item even after all the processing done to the timber sections.

Under the hurry of gluing, correct orientation of the inner layer’s crowns was ignored, ultimately affecting the stability of the finished plank.

Glue was leaking through the panel slats and sandpapering pads had to be used.

The edges had to be cleaned from the redundant material, getting to the geometry that was digitally analysed in Karamba and was later on physically milled with the KUKA robot.

D.I.Y. CLT Panel - front and side view: preparation of the 300x1600x80mm plank

Incorrect central layer crown orientations: grain direction should keep the same alternating pattern to increase structural homogeinity

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A.1 Making engineered timber A.1.1 Preparation and machining of a CLT panel

Treating the CLT panel as a homogenous sculptural medium. ‘Thickness optimised’ through structural analysis for a suitable loading scenario. At what resolution of lamellas can the anisotropic properties of timber be averaged to isotropic behaviour, if at all?

simplistic analysis of plank: bending moment, shear force and thikness optimisation diagrams are essential foundations that shape the principles behind the Karamba analysis (most of this part of the script was done by then team mate Bedir Bekar).

thickness optimised plank profile

four support points for the plank turning mesh in model into shell for finite element analysis

setting a gravity loadcase for the self-weight of the plank material properties defining a live loadcase distributed equally on the surface colour coding the graphical display for stress values Karamba structural analysis of plank

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original plank profile

bending moment diagram

structural analysis for topological optimisation

shear force diagram

A.1 Making engineered timber A.1.1 Preparation and machining of a CLT panel

Principal stress-lines from structural analysis

Milling toolpath diagram (passes reduced for diagrammatic purposes) 8

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Simulation of robot milling the plank

A.1 Making engineered timber A.1.1 Preparation and machining of a CLT panel

For the milling operation, a KUKA KR-60 robot (number indicating its power) was used. The time of the machining was 3 hours, the milling bit used was 16mm diameter ball-nosed and the roughing passes were of 10mm stepdown and 6mm step-over, with the finishing pass being having a five times smaller step-over.

Although the forces applied on the bench would be relatively low, too much of the required grain direction was removed, affecting its strength. Implementing an aggressive subtractive process was not suitable for this occasion, meaning that the steps should either not go that deep into the layers of the panel, or there should be more layers so that more of them would remain unmilled.

Calibrating the plank with the KR-60

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All the milling passes, where at the last one we are getting a more detailed, final pass of a denser toolpath for a fine finish

A.1 Making engineered timber A.1.1 Preparation and machining of a CLT panel Load from seated use

Loads transferred to ground through legs

finished bench elevation

bottom view of optimised plank: only a central part of the third layer has remained after the thickness optimisation. The grain direction is unsuitable because the tension is perpendicular to the grain

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side view of the milled surface: the plank sides and center are the areas that need most of material to withstand loads

A.1 Making engineered timber A.1.2 Manufacturing curved CLT panels Part of team with: Bedir Bekar

Evolving from the bench, our next try was to make two curved CLT panels, using three layers of thinner pine wood lamellas. Both panels were formed with the same technique, doing cold bending over a bespoke mold.

Getting to grips with wood lamellas proved to be vital in understanding materiality and bending limits, characteristics deeply inherent in the nature of bending-active structures. The first experiment with bending was plastic, where the deformation of the piece was intentionally permanent. Three layers of 6mm pine slats were placed and glued on top of each other, all together bent over a mold that forced the panel get to the desired shape. Alternating layers in perpendicular directions is a common characteristic for CLT and plywood, one core material used in the future explorations, albeit plywood can comprises of more or thinner layers.

‘Three-point’ mold for forming sinlgy curved CLT panels 11

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Placement of bottom layer curved lamellas

Clamped three-layer curved CLT panel

bending of panel under the pressure of clamps

A.1 Making engineered timber A.1.2 Manufacturing curved CLT panels

The finished CLT panel started having delaminations with the passage of time, mainly because of the absense of a press during the formation of it. The formation forces were not applied equally on the surfaces, with some marks on the final piece showcasing this.

After the lamination of the two CLT panels while dry-bending them on a jig, scanning came next in order to transfer the physical geometry into the digital world and feed the script for further robotic machining. After translating geometries from the physical to the digital, a KUKA robot was used to mill holes to receive pegs and laminate the two CLT panels with them in order to increase the structural volume. This step is further explained in the following section.

Three lamella thick curved CLT panel: 800 x 660 x 20mm thick

second curved CLT panel on top of the first: the difference in the geometries can be visible with a closer look at the small gap between the two panels

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A.1 Making engineered timber A.1.3 The introduction of the core layer Part of team with: Bedir Bekar

The notion of the core layer as a connector between two distant layers was first tested on a set of two curved CLT panels. In order to test the peg lamination in its simplest form, we fabricated the two panels described in the previous section, being of the same topology.

Any geometrical inaccuracies due to the analog methods of making that were descibed in the previous section were proven to be of minor importance, not affecting the peg lamination test that was later conducted. In order to import the physical geometries to the digital world, a 3D scanning process had to follow.

Scanning the CLT panels using the Creaform Handyscan scanner and VXelements software, the digital duplicates of the physical geometries were the material for the robotic operation, creating holes on the curved panels that would later receive the wooden pegs manually.

3D scanned CLT panel with positioning targets (dots) that allow for an automatic collage of 3D surfaces, combined to make the global piece

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A.1 Making engineered timber A.1.3 The introduction of the core layer

The pegs proved to add more rigidity to the system, without adding to its weight as much as a solid core layer would do.

In order to minimize machining time, both panels were machined at the same time. Nevertheless, not allowing any tolerance to the holes increased the assembling time and asked for higher forces to be exerted (hamerring from the top while pulling the pegs).

milling both CLT panels at once, having them fixed on a frame and then on a table, using clamps to reduce resonance and improve stability while milling

milling operation diagram with toolpath followed by the robot 14

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creating the desired gap beteween the two CLT panels and laminating with pegs, inserting them from the top

finished sandwich panel with peg lamination photo: Sarah Lever 15

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A.2 First active bending experiments Small scale models and hand assembly

Active-Bending is understood as an approach to generate curved structural form by means of elastic bending from initially straight or planar elements. Structures built on the basis of these principles are referred to as bending-active structures, harnessing bending for the creation of complex and lightweight designs (Lienhard, Schleicher and La Magna).

The first bending active experiments conducted were designed intuitively in the digital world, using a simple bandsaw to cut the pegs at length and a lasercutter for the holes of the plywood skins. Extra strength was provided with glue as no other type of connection was designed at that scale.

In pursuit of fluid wooden forms, the use of molds is significantly common. An external system applies constant formational forces onto the workpiece, until plastic (permanent) deformation occurs and the desired shape is achieved. A conventional mold has at least one surface along which the workpiece is shaped and can have a different nature and logic of making from the latter.

The complexity of the molds and the num active bending with peg lamination between two skins of the same topology: diagram showing the bending direction.

The deterministic relationship between the curved CLT panel and the mold had to be challenged by a construction method where the bent pieces could achieve geometries not tied to external factors. With active bending all the participants are part of the geometry and are responsible for the integrity of the system. The sum of the forces is internal, inherent in the structure and its constituent elements.

Explorations into active bending and lightweight, structural systems lead us to the use of plywood, in consideration of it being relatively strong, slender and flexible.

Plywood bends more along the grains of the external layers and this is a factor that defines the way a geometry is designed and later fabricated.

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the need for getting one of the surfaces immovable, urged us to use the temporary solution of a thread.

smaller scale model made with thin plywood sheets and dowels

A.3 Segmenting shell to developable strips A double curvature saddle geometry

In order to further explore the possibilities of creating freeform or doubly curved surfaces, we selected to study the ways of segmenting a more complex surface to simpler surfaces. Segmentation to strips is a technique that allows for an approximation of the original geometry, the accuracy of which depends on the xurvature extremity and the number of the strips (the greater the number, the closer one can get to the initial geometry). In order to be able to build the design, the strips needed to be developable, so as not to lose their geometric properties between the flat and their finished curved state. the right sequence of assembling can minimize breaks, applying less forces to the system.

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A.3 Segmenting shell to developable strips A double curvature saddle geometry

With the proper overlapping between the strips and respecting the bending limits of the material, we can be more confident that the designed geometry is feasible.

Regardless of the shape of the strips and the connecting points between them, there are differences in the comparison between the physical and the digital. The strips have a natural tendency to remain as flat as possible, translated into the geometrical mismatches between the initial digital design and the 3D scanned geometry.

the scanning process for evaluation of geometries and behavior of strips unveiled mismatches between digital model and its scanned equivalent 18

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A.4 Machining and assembling on a jig Two curved surfaces and peg lamination

Achieving the assembly between bending-active elements often requires a remarkable amount of strength and precision until the elements are forced to get the desired shape. The explorations performed with active bending proved that at least one of the two surfaces should be immovable so that the assembling phase becomes more feasible. The possibility of an extension of the making methods arose.

Making use of the standardized dimensions that a big plywood sheet comes from the factory, a subdivision of its surface informed the size of the jig. From the 6 by 2440 by 1220 millimeters birch plywood, a 1220 by 305 mm was the new unitized board. A structure of an elongated box, a wireframe of edges made of steel box sections and a set of leadscrews comprised the jig. Receiving two of those panels at a time, one on each side of the jig, the pieces could be first machined flat while each of them being attached vertically from 6 support/ control points.

Into Rhino’s Kangaroo physics simulation, every move of the 6 anchor points to a goal position would affect the surfaces, which would try to adapt to the changes and deform in an attempt to locally follow the new anchor points’ positions.

In the aftermath of the structural optimisation, the digital bent surfaces, the intersecting points and the vectors of the pegs had to be unrolled back to the flat, vertical position, in order to be machined on the KUKA robot.

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the components that comprise the jig and the assembled state of it

A.4 Machining and assembling on a jig Two curved surfaces and peg lamination

The two surfaces had to hang relatively far from the barycenter of the rotary table, in order to avoid collisions during the machining phase. The distance from the center of the table, the slenderness of the leadscrews and the imperfections in the components’ details leading to imperfect fits, increased the resonance during the milling operation. The vibrations affected the geometry and the position of the holes on the panels, also creating breakouts and splinters.

As a fact defined by the jig’s properties, the sheets attached on the jig had the capacity to only bend within a limit defined by the jig. Furthermore, working with a thicker material or overlaying more sheets would affect the bendability of the panels and might exceed the strength that the jig can hold regarding the bending phase. Any design changes in the unit size or thickness would require an update in the jig, where the overall structure would have to rely deeply on the segmentation that the tools would allow.

structural optimization with Silvereye plugin: optimizing the peg distribution using Kangaroo physics for the panels’ geometries and Karamba for the structural analysis, the goal being to minimize deformation

machining of the two panels: the jig, mounted on the robot’s rotary table, holding them flat in a vertical position.

Breakouts at the holes are visible due to resonance while machining.

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A.4 Machining and assembling on a jig Two curved surfaces and peg lamination

box sections with welded tubes for manipulating the wooden panels

steel profiles fasteners

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plane for the jig to sit on the robot’s rotary table

leadscrews and spacers

A.4 Machining and assembling on a jig Two curved surfaces and peg lamination

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flat plywood panels

removal of the lead screws and the top frame so that the laminated system can be lifted out of the jig

curved panels and later peg lamination that is done manually

laminated product (simplified and provisional)

A.4 Machining and assembling on a jig Two curved surfaces and peg lamination

jig and panels on the robot’s rotary table before the workpiece calibration 23

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closeup to the leadscrew component with which the positions of the 6 anchor points can be adjusted, and the preparation of the plywood panels to the correct formations by twisting the leadscrews manually

A.4 Machining and assembling on a jig Two curved surfaces and peg lamination

The two surfaces had to hang relatively far from the barycenter of the rotary table, in order to avoid collisions during the machining phase. The distance from the center of the table, the slenderness of the leadscrews and the imperfections in the components’ details leading to imperfect fits, increased the resonance during the milling operation. The vibrations affected the geometry and the position of the holes on the panels, also creating breakouts and splinters.

As a fact defined by the jig’s properties, the sheets attached on the jig had the capacity to only bend within a limit defined by the jig. Furthermore, working with a thicker material or overlaying more sheets would affect the bendability of the panels and might exceed the strength that the jig can hold regarding the bending phase. Any design changes in the unit size or thickness would require an update in the jig, where the overall structure would have to rely deeply on the segmentation that the tools would allow.

Subsequent to the implementation of the jig had to be a fabrication method that would increase again the possibilities in the design space. An adaptation to the design with one of the two skins flat, would simplify the assembling phase that could now happen manually. Fixing the straight sections (with the pegs fixed on them) on a flatbed would allow for the required adjustments to the bent surface. The robotic machining could happen at completely flat, unrolled surfaces, milled from greater plywood sheets attached on the top side of a table.

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the machined and assembled component before its removal from the jig: moderate bending ability because of the jig geometry.

A.5 Bending active floor segment Two curved surfaces and peg lamination

The next full-scale experiment was a segment of a floor, where the bottom surface would be geometrically informed by the forces applied to the top of the structure. In a case study, a unified load and a point load, representing a human standing in the center of the structure, were applied to a surface of a 2x1.2m footprint, equally segmented to three parts of 40cm width each. For one of the segments that was fabricated (using the same technique for the rest of them) the bottom surface was made out of a single 6mm thick birch plywood. In order to get a more accurate orientation of the 25mm thick pegs that would come at a later stage in the design, the top surface had double thickness, namely 12mm. With this method the wall of the connection between the panel and the pegs would be higher, resulting to a stiffer detail that would guide the pegs to the right positions.

The workflow comprised of four discrete steps which shared some geometrical similarities: the digital design would give curved geometries with the milling information (holes for the pegs) attached to them. Unrolling the geometries flat and mapping this information correctly (the holes would need to keep their relative positions and orientations) would render the pieces workable for the robot. After the machining, the assembling phase would get all in the desired shape which should approximate the curved, digital geometry to the greatest possible extent.

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transformation from a flat surface to an optimized bending active floor component, laminated with pegs

digital - curved (designing)

physical - flat (machining)

digital - flat (unrolling)

physical - curved (assembling)

workflow from digital to physical: from curved shapes to flat, then back to curved

A.5 Bending active floor segment Two curved surfaces and peg lamination

Next in the sequence was the translation of the bottom surface to a shape that could be achieved with a continuous plywood sheet. To simplify the structure and make the outcomes of the exploration more apparent, we aimed at getting a continuous curved profile along the whole width of the floor system.

The displacement informed the creation of the bottom surface that would later come to reinforce the system.

The bottom skin geometry was still unrefined, raw and segmented, following the analysis diagram without yet being geometrically translated by the material it would be made of.

Diagram of forces applied to the floor with an even distribution of loads and an additional point load in the center of the structure.

Pegs were distributed evenly along the structure, to justify the analysis which was ran for one more time, including the top surface, the pegs in the middle and the bottom, tessellated and still unrefined skin.

The translation of the diagram to a single profile informed by the greatest displacement values at the center of the structure

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A.5 Bending active floor segment Two curved surfaces and peg lamination

After the intial shape, the bottom geometry had still to get refined and approximate a surface undergoing elastic bending: to design a more intricate bended geometry, we first ought to understand and predict its behavior. James Bernoulli in 1691 was the first to formulate the notion of the elastica. In terms of mechanics and material behavior it can be translated to a curve with both end points fixed and the mechanical equilibrium of forces along the curve (Levien). a bending simulation was executed: the initial curve had to be redesigned and approximated by one of the same lengths, undergoing elastic bending. Inside Kangaroo, a set of control points forced the curve to bend elastically. While the curve was being bent due to the control (anchor) points forcing it to shape, a script calculated the maximum deviation between the two curves that were compared. In order to get more iterations of the bended geometry, the evolutionary solver Galapagos was used. Moving the control points at various places along the curve and aiming for a minimum deviation between the two curves, the component would attempt to approximate the initial curve to the greatest degree.

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The Grasshopper code showing the control points forcing the curve to bend elastically, the calculation of the deviation between the two curves and the two evolutionary solvers that approximate the best curve fit and the point with the greatest curvature with Kangaroo bending forces

The initial curve and the bent equivalent of it with the point of the greatest curvature

A.5 Bending active floor segment Two curved surfaces and peg lamination

Through a Karamba structural optimization executed with an evolutionary solver, the culled pegs’ positions were defined. Setting a goal of minimizing the global model displacement while adjusting the pegs’ endpoints gave the position of them. Utilization had to be less than the value of hundred to ensure that the components would not fail under loads. designed geometry material distribution

optimization

Representation of the digital model before the structural optimization and the culling of the pegs

structural performance

analysis

Structural optimization diagram: the workflow

One of the many possible optimized alternative solutions of the structure diagram

Utilization view of the pegs (beam view) and the surfaces (shell view) being within acceptable values

Floor segment top view

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A.5 Bending active floor segment Two curved surfaces and peg lamination

For the machining part of the floor section, a KUKA KR60 robot was used for milling the holes on the panels.

A code that was exported from the Robots plugin from Grasshopper and executed on the stock birch plywood panels, clamped firmly on a flat table. The existence of a vacuum bed similar to those used with the CNC milling machines would provide better results since the stock material would have an even better grip.

The robotic toolpath, exported from the Grasshopper plugin Robots, included the required operations for machining each one of the surfaces: milling of the peg holes and preparation of the side lap joint (for the later assembling of the segment with the other segments, not executed at the end)

Machining of one surface of the floor segment with the KUKA robot. The square corner at the right of the image provides the same positioning of all the stock materials, saving time from calibrating after each operation 29

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Robotic toolpath for machining one of the floor’s surfaces

A.5 Bending active floor segment Two curved surfaces and peg lamination

The next stage to follow was the assembling of the floor segment, inverting the top and bottom skins: the thicker, top surface was clamped on a table and all the pegs that had similar orientation were hammered in their holes. It became apparent that due to the pegs coming at different angles, it was impractical to fix all the pegs and subsequently bend and fix the bottom, thinner surface at once. Because of the bottom surface tendency to spring back to its flat condition, ratchet straps were employed, escorted by several clamps that were placed near the areas of curvature changes.

The edges of the top and bottom surfaces had to align and the global geometry had to be approximated with the ratchet straps, before the remaining pegs would come and lock everything in shape.

The bending active and the flat surface with the peg lamination between them 30

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Ratchet straps were forcing the bottom surface in shape until the pegs come in position. The final geometry with the straps removed where the pegs keep the bending active surface in its new, geometrical state. 3D scanning unveiled geometrical inaccuracies due to high forces and curvatures that were more extreme than the material allowed for active bending.

Bending active floor segment supported at its two ends.

The curvature between the two peg clusters changes, having compression (center) and tension (ends)

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finished floor segment with peg lamination photo: Sarah Lever

A.6 From single pegs to nodes

After some peg detailing tests done with single pegs meeting the plywood surfaces (explained in section A.8), the 3D printed multinode was next to be implemented. Inspired by a bone section where the area closer to the external border is more busy compared to the core (cortical-trabecular bone), a network of pegs would have their end points meeting at a series of nodes. In order to spread the loads applied on the surface through the nodes, a flat surface with more than one connecting points to the plywood was used as the base of each node, distributing the forces to greater surfaces (minimizing pressure).

The first iteration was an 1:3 scale model with joints printed with PLA filament and the forest of pegs (being of a great number and of 3mm thickness between 2mm birch plywood) were glued to the nodes.

A Karamba structural analysis was conducted, the outcomes of which were less successful at some areas of the fabricated model: areas with big gaps of nodes proved to give more flex to the surface than needed, affecting the implementation of the initial design. A more rationalized distribution would make a stronger structure, something that was proven at the higher areas of the model with nodes alternating from the left to the right.

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The aim of the peg optimization had switched from the structural aspect of it to the geometrical one. This is when Kangaroo physics and the simulation of bending the geometries, replaced Karamba. For relatively slender surfaces (the thin plywood sheets we designed to use in comparison to their length lies in that category) Kangaroo can simulate the bending behavior of the structure. When used in parallel with an evolutionary solver (Octopus was used here), the goal being to minimize displacement, the peg distribution could get a meaning.

Some areas of support would still need to be inserted manualy (the ends of the surfaces where there is the greatest tendency to spring back due to elastic bending).

Scale prototype. less pegs and lower concentration of nodes at the base of the structure give more flex than needed. This knowledge was transfered to the next exploration. photo: Sarah Lever

A.6 From single pegs to nodes

The first step to the design is to import the two geometries. Connecting the Octopus evolutionary solver to the number sliders comes next, where the sliders define the points on the surfaces. The solver tries to minimize the displacement of the structure while changing the position of the pegs and the nodes.

Duplicate points are removed, connections between the points are created and the lines (after getting a thickness) that intersect with the others are removed from the list. Since this removal affects the sequence of the curves’ list, a new “closest geometry� components needs to be employed in order to collect the lines to batches based on their starting points.

Import of geometries and number sliders representing the points on the surfaces 34

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List with the number of the nodes for one of the surfaces and the number of pegs that each one of them receives

Writing the holes numbers for the nodes on the surfaces and later unrolling of them to be laser cut

Displacement is the goal for the optimization

pegs as lines and nodes as points unrolled on surface

A.6 From single pegs to nodes

The assembling process followed here, which will be applied to the next full scale model, was to assemble the network and then force the birch plywood surfaces onto it. Some marks showing the sequence and the orientation of the nodes, as well as the length of the pegs used at each point, would simplify the assembling process.

photo: Sarah Lever

A.7 Bending active symbiotic surfaces Four plywood surfaces of different thickness and curvature, weaved within a network of nodes and pegs

The project tries to build a mutually symbiotic relationship between elastically bent birch plywood sheets that actively seek their own forms. This relationship is a product of a forest of wooden pegs anchored in a way to minimize geometrical deformation. What connects the pegs to the sheets is an array of intelligent nodes that allow for easy disassemblage in situ.

The versatility of the project hypothesis ensures application at all scales, ranging from furniture to habitable spaces where the purpose of the elements is increments from mere geometrical to added structural demands.

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2440x300x6mm birch ply 3

2440x300x6mm birch ply 2100x300x2mm birch ply 2400x300x4mm birch ply Areas of peg families, within the bounds of which separate optimization and geometrical simulation was executed.

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In order to stress the interdependence of the surfaces and the contribution of all the components to the system, the design became more secluded from the external world, creating a universe where surfaces, pegs and nodes act as one.

Similar to the previous prototype, the manufacturing approach here is deterministic. Everything is designed, the holes are drilled, the pegs are cut in length, the nodes and the details are properly designed and fabricated for the high time of the assembly.

With a width of 1.3m, a height of 2.3m and a thickness of 0.3m, the artefact is the outcome of a fight between four birch plywood surfaces and a network of oak pegs.

The external surfaces are 6mm thick, the one in the middle is 4mm and the closed shape in the core of the structure is 2mm thick birch plywood. The curvature achieved is dependent on the thickness of the material and informed the decision for the layering sequence of the surfaces.

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The pegs are oak wood, 9mm thick for segments one to 6, 12mm thick for segment 7 and 18mm thick for segment 8, according to the length, their population size and the local tendency (highest curvature) of the surfaces to spring back due to active bending.

A.7 Bending active symbiotic surfaces Four plywood surfaces of different thickness and curvature, weaved within a network of nodes and pegs

In order to ensure that the designed geometries are feasible, physical bending tests were done with hands, bending the strips to their extremes and defining their bending limits. Due to the deterministic nature of the project, all the geometries need to be explicitly designed and anticipated before the assembling phase.

The area of interest had shifted towards a geometrical approach for the symbiotic nature of the pegs and the surfaces. In detail, the system comprises of the following:

As an extra security check, the initial design was printed and the strips were bent on top of the printed paper, making the required adjustments once again.

-The symbiotic plywood surfaces

Bending the 6mm birch ply to understand its bending limitations 37

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- The pegs

- The nodes with arms that connect the pegs to the surfaces

Initial sketches of surface’s symbiotic nature

Tracing the geometries over the first iteration that further refined the design: the edges of the surfaces were affected the most.

A.7 Bending active symbiotic surfaces Four plywood surfaces of different thickness and curvature, weaved within a network of nodes and pegs

In order to select the pegs’ positions, we did an optimization where Kangaroo was redoing the active bending simulation multiple times, trying to minimise displacement in the output geometries. The simulation/optimization ran in the increments (1 to 8) described previously. A one-go optimization for the whole structure would not give useful outcomes because there would be no reference point to compare the outcomes against.

Displacement read as length of lines between the initial geometry and the simulation run through Kangaroo: greater attention with the pegs potition needs to be paid at the areas with high curvature and at the end of the strips 38

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Kangaroo inputs of geometries and pegs, being altered by Octopus evolutionary solver. Zombie Solver to the right ensures that the output is fed back to the solver after a specific time that is enough for the geometry to start fighting for its natural condition

A.7 Bending active symbiotic surfaces Four plywood surfaces of different thickness and curvature, weaved within a network of nodes and pegs

Some of the Octopus optimization processes done for the segmented structure, opting for minimising deflection and the number of the nodes. Trying to keep the logic of a failry even distribution along the surfaces and with the need to reinforce the edges of them, the optimization could not work without some manual inputs by the user 39

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A.7 Bending active symbiotic surfaces Four plywood surfaces of different thickness and curvature, weaved within a network of nodes and pegs

Due to the irrational geometry of the nodes, having their arms at irregular orientations, an additive manufacturing idea and, more specifically, 3D printing was implemented. Due to the need for clearance between the top and bottom parts of the snap fit joint, the normal 3D printing with PLA filament would require support material to build higher than the slots. For that reason and for increasing the strength of the connections, the method of SLS printing was selected.

Tests were conducted to ensure the durability of the connection so that the snap fit joint does remain in place within limits of forces applied to it. The tests were done with simple PLA printed joints denoting that its SLS equivalent would surpass the desired standards.

In order to simplify assembling, the initial thought was to nest pegs into families of lengths and have the printed node compromise for the length difference.

Unfortunately the extremely high cost of SLS printing dictated to keep the printed parts to their minimal volume, having the pegs to take up for the length differences (similar to prototype in section A.6).

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A.7 Bending active symbiotic surfaces Four plywood surfaces of different thickness and curvature, weaved within a network of nodes and pegs

All the nodes have a pin on their base, extending towards the surface and securing them from sliding on it. two holes receive the fixings on the surface.

The nodes of the middle 4mm layer surface share the same spot with their neighbours in an attempt to leave the surface as unperforated as possible. A specific design with a pin and a slot was designed so that the two facing nodes can snap in place together, sharing the same fixings on the surface.

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A.7 Bending active symbiotic surfaces

2300mm

Four plywood surfaces of different thickness and curvature, weaved within a network of nodes and pegs

1300mm

300mm

Front view of the whole structure and side view of the pegs-nodes network, where color coding relates to the segmentations of the analysis 42

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SLS printed node before dye

hole to pinch and release the snap fit joint

labelling of the node and pin that securely locates the node in place

tappex M4 insert for bolts

soldering iron for melting insert into the plastic

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A.8 List of peg details

In order to simplify the workflow, a switch was done from the robot (providing holes at an angle) to simplier ways of production, such as a lasercutter or even a hand drill. This method would give straight holes going perpendicular to the stock material, requiring the angle of the peg to be taken by the geometry of the latter. Cuting pegs at an angle and using the offcuts, wood inserts and woodscrews where tested, all presented in the following list.

Throughout all the previous explorations, a key part was played by the peg detail and the way it meets the surfaces. After tries with wedges, glue, and wood inserts, the detail would become either unstable or too complicated, increasing the fabricating and assembling time.

A list of the joint methods that were tested concluded the detail to the node where bespoke SLS printed nodes would receive a forest of pegs, increasing structural efficiency and providing the potential of an application to the scale of a building.

Detail 1 - wedge and glue The detail used at the floor segment described in a previous section. The main reasons it failed are the following: low accuracy - the peg can either be in tension or compression and the wedge should secure it from movements in either direction. A mechanical connection could be more reliable than glue in this case.

Detail 2 - peg, offcut 1, offcut 2 Main peg body and the two offcuts. Only a small hole on the laser cutter would be needed for the screw to go through. the hole would need to be more like an elongated slot in order to compromise for the peg angle, letting the peg rest.

Using a simple woodscrew to connect the offcuts with the main peg body showed disadvantaged of aligning the pieces and splits occured. As a consequence, the quest for a more mechanical connection rose.

Detail 3 - wood inserts A wood insert is threaded in the main body of the peg. There were some splits at the offcuts and the inserts broke after some lateral forces, proved to be unsuitable for this type of connection. Apart from not being a reliable detail for the above mentioned reasons, this detail and detail 2 were abandoned because machining such slender pieces of wood parallel to the grain decreases dramatically the strength of them.

Detail 4 - 3D printed node The decision to keep the pegs as much intact as possible lead us to the next detail type that shows the greatest potential in terms of strength, machining and assembling time. A printed node would take all the odd geometric formations and allow for multiple pegs to orient freely.

A shoulder would allow the loads not to be concentrated to a point and a pin would let the node lock in place.

Detail 5 - snap fit joint Applicable to joints 2,3: Unrolled peg profiles with intersecting surfaces. After printing the paper, rolling it back to the physical peg and cutting it on the bandsaw is next.

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This detail was designed and refined to have an easy assembly for the pegs to the nodes. The free rotation of the top part against the arm of the node releases the maker from the duty to align the holes at both ends of the peg that would connect it to the two nodes (one on each side). The pinch release holes provide an easy disassembly at any time.

B a p p e n d i x

or other material that contributed to the author’s progress

B.1 Design of a parametric pavilion

Dealing with tree structures in Grasshopper and first meeting with Kangaroo and Karamba. Modelling process: a pavillion comprising of three parametric walls designed with different techniques, a parametric canopy with structural analysis and an ornamental skin on the roof.

Skin on wall No 1 using Kangaroo physics and Weaverbird

Canopy structural analysis: perspective top view

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Structural analysis on canopy frame using Karamba. Having lines as inputs (representing beams and columns) the analysis outputs come as values or visualising diagrams, helping the user change the structure if needed

B.1 Design of a parametric pavilion

ornamental roof skin

wall No 1: side view and detail. Truss of differentiating length elements according to attractor point, skin made with Kangaroo plugin canopy structure

parametric wall No 1

unlevel ground

wall No 2: side view and detail. Initial surface division into segments. Rectangular shaped holes, size defined by attractor point

parametric wall No 2

parametric wall No 3 wall No 3: side view and detail. Populating a geometry over paths. Rectangular bricks with circular holes, size defined by attractor point 52

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B.2 Design and fabrication of a vehicle An expandable wheel structure Part of team with: Lutz Barndt, Matthew Osbourne, Amir Arsalan Tahouni, Jia Wan. Work presented here is part of the author’s contribution.

Laser cut plywood pieces get assembled with steel bars passing through them. The plywood holes are filled with 3D printed shoulder washers, being firmly placed against the wood. Friction is reduced since the plywood arms do not touch directly the bar and there is the 3D printed shoulder washer instead. The shoulder washers keep the plywood elements apart so that there is less friction. A plain 3D printed washer is placed after the plywood and then a cotter pin locks everything in place.

washer and shoulder washer next to the other components to be assembled together: isometric

The 3D printed elements were bespoke, solid components and thus could replace typical steel washers.

assembling sequence of elements. The shoulder washer fills the plywood gap to reduce rotation friction, the washer protects the plywood from the cotter pin: exploded axonometric

3D printed shoulder nut and washer 53

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joint detail with 3D printed washer

all components assembled in place: digital representation

B.2 Design and fabrication of a vehicle An expandable wheel structure

photo: Sarah Lever

B.3 Robotic milled joints

Modelling process: Design and simulation of milling a four joints timber frame consisting of two different sets of joints. Each timber element’s ends are a male (m) and a female (f) joint of the two different types. The main grasshopper plugin used was Robots.

Apart from the apparent chance to deal with robotic machining and further extending the computational skills, fittings and tolerances were also an important gain.

Simulation of first material removal for male joint

Simulation of facing off one side of a beam in order to get the desired final length, regardless of the raw material length 55

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Robotic milled joints

tenon and mortise joint with mitered face detail: male and female

complete set of four timber pieces 2x4 inches cross section

double pocket joint detail: male and female

robotic milling of male double pocket joint

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Thank you.