Synthesis of design production with integrated digital ... · Keywords: Digital fabrication; Rule-based design 1. Introduction For architects a portion of design production is expressed

16 (2007) 298–310www.elsevier.com/locate/autcon

Automation in Construction

Synthesis of design production with integrated digital fabrication

Lawrence Sass

Department of Architecture, Massachusetts Institute of Technology, United States

Accepted 30 June 2006

Abstract

Presented is a research project that demonstrates cross-scale design production with physical examples. Designers today have begun usingrapid prototyping to materialize designs of a variety of materials from plastic to metal and ceramics. They also use CAD/CAM to materializefull-scale building components during construction with metal, stone, and a variety of woods. Dilemmas are found in the translation of adescription that drives rapid prototyping tools and descriptions that drive CAD/CAM machinery for full-scale component manufacturing. Thispaper presents a method to produce designs with test results that drive varying types of digital fabrication devices across scales from onegeometric file. Presented is an integration of machines, materials, and modeling resulting as a full-scale house and a redefinition of con-struction components, assembly and building shape. Final results demonstrate a relationship between design artifacts built by rapid prototypingand full-scale CNC construction.© 2006 Elsevier B.V. All rights reserved.

Keywords: Digital fabrication; Rule-based design

1. Introduction

For architects a portion of design production is expressedphysically through desktop models and mockups. Since thedays of the Renaissance, execution of physical models fordesign production at any scale has been a process of manualtranslation from design drawings to physical model or buildingartifacts. Today design production is changing rapidly, asarchitects increasingly use computers to generate designs andthen digital fabrication to build models for design review.Downstream many contractors have also incorporated CAD/CAM into their practices as a means to produce full-scalebuilding components. This new production method, with virtualand physical models throughout design and construction,diminishes the need for architectural drawings as the catalystfor design production. As a next step in the evolution of digitalfabrication, this paper presents a novel means of producingdesigns as an integrated production process. For architects anddesigners of physically large products (boats, airplanes, etc.),digital fabrication comprises two distinct subfields: rapid

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prototyping for model making [1], and CNC (also referred toas CAD/CAM) fabricating for building components [2]. It isproblematic that each field requires its own distinct descriptionin CAD for fabrication. Designers building virtual 3D modelsmay find that digital fabrication inhibits workflow because toomany laborious steps are required in model translation betweenmachines and across artifact scales. This research explores adesire to create coordinated device descriptions that ultimatelyallow for design production at all scales. Results of this workwill demonstrate that an integrated system shortens productdevelopment time for near-instant manufacturing from designmodels. The examples presented here demonstrate devicecoordination between cardboard desktop models and wood-framed construction.

For some time, research in product modeling has ex-pressed a need to integrate CAD/CAM manufacturing intoproduct model geometry [3–5]. In particular, CAD/CAMintegration has the potential for reducing paper documen-tation by allowing product model geometry to drive com-ponent production. Missing from product model research,however, is the relationship between a final product modeland descriptions for CAD/CAM geometry. Also missing arethe methods to generate CAD/CAM geometry as part of pro-

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Fig. 1. (A) Computer rendering of design description for the shelter and (B) partial computer rendering of components in 3D.

299L. Sass / Automation in Construction 16 (2007) 298–310

duct model generation and the logic behind the choice ofgeometric descriptions.

To demonstrate the benefits and problems associated withdevice and software integration, three physical artifacts ofa small building design (the Instant Shelter) were generatedin CAD. These machine-quality artifacts were built fromsimilar geometries with two digital fabrication devices. Theproduction process starts by deconstructing a CSG model(Fig. 1) into components. In this research these componentsare manufactured by laser-cutting cardboard and assemblingby hand (Fig. 2). In theory, after design approval, the sameinformation is used to manufacture components of a shelterwith a CNC wood mill at full-scale construction (Fig. 3).The system of modeling presented here takes advantageof machine precision, tolerance, and flexibilities in modelingby integrating mating assemblies into each manufacturedcomponent. The design example–the Instant Shelter–is aflat-pack manufacturing and shipping system for people inneed of low-cost housing. This entire shelter can be man-ufactured on site from (1) a stack of plywood, (2) a CNCrouter (Gantry arm and table only), (3) a rubber mallet, (4) acrowbar, and (5) a computer. Manufactured of precise ply-wood components, the Instant Shelter is a habitable structurebuilt of one material (plywood), assembled with muscle anda rubber mallet (Fig. 4). Nails, screws, or glue are not usedfor assembly, as each component is connected to a corres-ponding component with embedded joinery that sustainsassembly by friction only. For future investigations into de-

Fig. 2. Artifact A is a laser-cut model of cardboard with six supporting piers,studs, and partial attachment of inner sheathing.

sign systems for digital fabrication, this study will serve asan experimental control from which new shelter designs canbe measured (Fig. 5).

A novel method for designing and constructing a smallbuilding was discovered as a result of this research exploration.Device integration revealed designed products with uniquemethods for physical assembly and CAD representation. Fromthe physical examples, two areas of design production aredescribed in this paper:

(a) First, is a new description of building components inCAD based on digital fabrication devices. Presented is arestructure of component joinery that takes advantage ofmachine precision and control in CAD.

(b) Second, reasoning through design with geometricdescriptions built and constrained by the relationshipbetween materials, machine function (drilling) and modelassembly.

2. Background

2.1. Rapid production by lateral contouring

Rapid prototyping machinery is used by designers in awide array of fields for producing physical models from vir-tual product models [6]. Models are built by lateral slicing ofa CAD model into paper-thin sections. Next, machine tools

Fig. 3. CNC router with 1/2″ bit used to manufacture components.

Fig. 4. Assembly of 1:1 plywood components assembled with a rubber mallet.

Fig. 5. Conceptual computer renderings of possible design descriptionsconstrained by the limitations of fabrication rules.

300 L. Sass / Automation in Construction 16 (2007) 298–310

rapidly manufacture individual model contours or curves andassemble to previously built contours in a single process(Fig. 6b). These models are then used for design evaluationprior to full-scale manufacturing or mass production [7].Advantages of rapid prototyping for architectural design arethat the medium allows for communication of complex 3Dconcepts and supports the testing of nonstandard buildingcomponents as direct translations from the design model.Workflow for rapid prototyping starts with a solid 3D file(stl) as meshed information, a file format established by 3DSystems, Inc. [8]. Models are produced in steps models withintervals defined by the machine software [9]. This processwas initially defined as stereolithography where plastic-likearticles are built of layers of exposed photo-sensitive ma-terial. Alternative 3D printing is a similar process that buildsa model by bonding layers with an adhesive sprayed ontoa layer of powder. After manufacturing, post-processing isrequired to remove loose powder before a hardening liquid isinfused [10]. Another method for model building is shapedeposition manufacturing (SDM) [11], where layers of ma-terial are deposited as a liquid atop previously depositedlayers. This technique is employed by Stratasys rapid man-ufacturing systems, defined as Fuse Deposition Modeling(FDM). For an overview of the most recent rapid prototypingmethods, see Cooper [12] and Chua et al. [13].

2.2. Designing with CNC mills

Until recently, CAD/CAM production has centered onindustrial applications for mass-manufactured products suchas airplane and automobile parts [14]. Today CAD/CAM orCNC machinery is also used to manufacture many items forshort manufacturing runs of specialty products. Particular tothis study, CNC manufacturing has seen extensive use inprocessing wood products such as kitchen cabinets, stair-cases, and furniture from virtual models and drawings. Ofthe array of CNC machines available to designers (lathesand multi-axis mills), mills tend to be the top choice becauseof their simplicity and outcome control [15]. CNC productionstarts with a 2D or 3D description as a virtual model. Forsome 3D descriptions, digital fabrication begins with solid

stock that is milled to the shape of the virtual model. Forother 3D shapes (in particular, very large 3D descriptions),solid geometry is subdivided into 2D components in 3Dspace, then flattened to a 2D position for translation to CAMsoftware (Fig. 3). To reduce time in translation from a designmodel to tool paths, advanced research generates tool pathsby way of programming directly in G and M code languages[16]. Mark presents a method to model and manufacture byprogramming, visualizing, and fabricating within one CADenvironment. For an overview of CNC milling and alter-native machine application, see Kunwoo [17]. Because thefield of architecture demands such a wide array of scaledoutputs in terms of physical size, architects use CNC millingin one of two modes. The first is CNC milling for archi-tectural model making as a way of building furniture-sizeearly-phase and final physical models from one mill [18].A second mode of operation has been the manufacture ofcomponents for full-scale construction; for examples, seeSchodek et al. [19].

2.3. Shortcomings

Both production methods result in high-quality output assolid physical artifacts. Integration between rapid prototypingand CNC machines is faced with two limiting factors, however.

First, descriptions for rapid prototyping devices in terms ofmaterials and tool paths are not compatible with CNCmachinery for full-scale construction. For example, a 3DCAD model processed by a rapid prototyping machine as alayered process that cannot be used to mill full-scale kitchencabinetry from lumber. Manufacturing geometries with under-cuts may not be possible with most milling machines. As wellstacked layers of material are not the most efficient way tobuild a physically large product such as a building. A newdescription is needed for CNC fabrication–one that considerstools, tool paths, materials, and ways to reduce geometry totool paths.

Second, geometric descriptions for lumber (2″×4″) andlumber assembly are incompatible with standard CNC mills.Traditional wood-frame construction is based on reference to

Fig. 6. Stages of descriptions from a virtual solid in CAD (a) to rapid prototyping (b) to bilaterally contoured structure between two surfaces (c).


paper-based forms of communication, handcrafted componentmanufacture, and inaccurate building assembly. A typical wallbuilt of wood studs, plywood sheathing, and sheet rock isdesigned for rough assembly with a nail gun and imprecisecutting with machine-powered saws (Fig. 7a). For industriesthat manufacture with CNC machinery precision is anintegrated function that affects most (if not all) of the part andassembly process. As long as hand manufacture and assemblyand paper-based communication are in place, machine precisionfor building components will not aid legacy constructionmethods.

3. Descriptions for fabrication

3.1. Device coordination system

A foundation for integrating digital fabrication devices mustbe based on a rethinking of tool path goals and artifact assembly

Fig. 7. Legacy assembly of wood frame construction (a) in contrast with CNC co

methods. To meet this goal, geometric descriptions are neededthat coordinate geometries between device types. This sectionpresents new descriptions based on the following threecharacteristics:

(1) materials: one material type for both machines (in thisresearch, flat solid material)

(2) artifact structure: nonlayered model building methods(3) material joining: components fabricated with mating

assemblies.

3.2. Structural descriptions

Rapid prototyping builds objects by assembly of laterallysliced contours of a consistent step [fs] from a solid model (Fig.6b). An improved product description for rapid manufactureacross scales is bilateral contouring for structure with surfacingpanels for strength, as opposed to typical lateral slicing (Fig. 6c)

nstruction methods that use one material type with integral attachments (b).


[20]. An infrastructure typically found within aerospace,automotive, and shipbuilding industries, bilateral contouringis an organized array of horizontal and vertical interlocking ribsevenly stepped along a surface. Defined by the user, contourspacing [fν] [fh] can be many times greater than the lateralslicing found in traditional rapid prototyping with similarstrength. These structures are monocoque and semi-monocoqueassemblies composed of structural ribs and skinning attached byrivets and adhesives. The relationship between digital fabrica-tion devices offers fast, simple means of manufacturing ribs atrelative design scales. For this research, descriptions of this typestart as 3D models ultimately translated to 2D geometries fordigitally controlled cutting. These descriptions also includenotching for attachment to perpendicular ribs and a strategy forsurfacing to bond ribs. Difficulties in attaching surfaces tobilaterally contoured structures limit the application of thismethod in non-mass-manufacturing fields such as architecture.Surfacing strategies for curved contours are especially difficultto devise.

3.3. Joining

A second solution for device integration is found by theredefinition of component joinery. A novel approach to as-sembly found in this research removes the need for secondaryassembly mechanics (screws or nails) by embedding the logic ofcomponent assembly within the geometry of each component.Assembly strategies are critical for products manufactured withhigh levels of precision. A subfunction of an assembly isjoining, which brings together many components to serve someparticular function [21]. In full-scale construction, standardmethods of joining building components such as sheathing andstuds are screws, nails, and high-strength adhesives. Long-term imprecision in manufacturing or assembly can lead to asignificant decrease in product quality and an increase in con-struction labor from variations in assembly types and methods[22]. Effective assembly for bilaterally contoured structureswith computers is achieved here by embedding slots into sheath-ing that corresponds with each rib. Precision and flexibilities inboth machines and software make it possible for assemblyintegration to be part of component geometry. Sample studiesleading up to this research have demonstrated that attachmentsintegrated into components allow for fast component assembly[23].

3.4. Joining with integral attachments

Beginning in the 1990s, the plastics industry consideredways to rethink component attachment for consumer-relatedproducts. Researchers in this field explored a variety of waysto build and connect parts by alignment and part-interlockingonly, referred to as integral attachment [24]. With respectto plastics, mechanical joining of components is achieved byway of mating parts manufactured with each component.Typically known as snap-fit, integral assembly features suchas dovetails, slots, and tabs are ideal for aligning and as-sembling components at any scale [25]. Research in this paper

uses integral attachments to join plywood components withnegative or positive appendages. A major benefit of workingwith integral attachments is that any component can be as-signed a mating component strategically placed on the part.Workflow in building component geometry means that as-sembly and attachment control occurs in design, not in thefield. Integral attachment design must judge many constrain-ing factors, such as functionality, component shape, locking,assembly motion, and robustness as related to tolerance andstrength. Finite element analysis provides a means to testconnections for stress strain. Also, methods of measuring thestrength of integral attachments for nonlinear force-deflectioncurves and engagement for individual components have beenestablished [26,27].

3.5. Existing forms of joinery

Current examples confirm that geometric generation ofcomponent geometry with mating attachments can be pro-grammed as a generative function in CAD, as demonstrated byKilian [28]. Kilian presents a program that joins aluminumsheets with interlocking cutouts at component edges (i.e., azipper-like joint). The two parts are cut by water jet, and theprogram enables the component and assembly to be manufac-tured as a single unit. Variables in the program address materialthickness, tolerance between parts, and variation in height andlength for each tooth of the zipper. There also exists industrialsoftware, such as Industrial Origami, that can be used to bendvery thick metal sheets by stamping curved cutouts into flatsheets [29]. After stamping occurs, attachments are built into thefinal part cutout. Lamina Design is one software package thattranslates freeform 3D designs to 2D positions for digitalfabrication of plastic, metal, and wood sheet material [30]. Suchsoftware packages produce descriptions for product manufac-ture as single objects with integral attachments. For houses,built of many components and material types, rule structuresare needed to guide the generation of the myriad interrelatedcomponents.

3.6. Workflow

Field testing of a design description built with bilateralcontouring and integral attachments at two scales, built with twomachine types, confirmed the possibility of device integration.Three digital mockups of building corners, walls, and roofsections illuminated the limits of machine tolerance andassembly strength as well as the best practices for assemblyorder. Testing of the joinery was focused on understanding themechanical behaviors of plywood assemblies between sheath-ing, studs, and integral attachments (Fig. 7b). Mockupworkflow began with solid models subdivided to internal andexternal panels (of 3/4ʺ plywood) (Fig. 8a). Outer and innersheathing was attached by way of integral attachments spacedat 3 tabs per stud/sheath in 3D space (Fig. 8b). Last, elementsare translated to 2D for cutting (Fig. 8c). For physicalevaluation, digital mockups were first built of laser-cutcardboard pieces to test for part assembly and layout in 2D

Fig. 8. Workflow for digital manufacturing from a design description (a) to a 3D construction model as 3/4″ thick plywood components (b) to horizontal cut sheets for4′×8′ plywood (c).


(Fig. 9A). Later, mockups were built at full-scale of plywood;strength was gained from material swelling between interlock-ing components by outdoor weathering (rain) (Fig. 9B).Complications in the system were discovered when wallsturned to corners or where three surfaces met, such as a roofhip or walls to roofing. Digital mockups at surface transitionsdemonstrated a need for finer grained assemblies allowing forcomplex turns at corners (Fig. 9). Through initial physicaltests, an array of walls, flooring, and roof types confirmedstructural stability for any surface type. Digital mockupsconfirmed state restoration of 3D virtual geometries as physicalbuilding elements.

4. Reasoning with digital fabrication

Described in this section is the foundation of an automateddesign system based on constraints associated with digitalfabrication. Aspirations are driven toward a formal languagethat supports creative design with digital fabrication in mind.As defined by Stiny, a formalized process for designautomation requires that elements be organized by twofactors: rules that compose elements, and rules that describethe elements' functions (purpose, use, type, etc.) [31]. Brownet al. present a formal language for fabrication that embodiesrules for machine function and descriptions [32]. Theirresearch makes possible an understanding of manufacturingas a grammar with rules associated to machining andmaterials. In this section, two descriptions are discussed insearch of a language based on formal functional rules and

Fig. 9. (A) Digital mock-up of corner assembly tested first of cardboard and la

rules for part description. Combined, these two descriptiontypes enable the construct of highly precise artifacts. The twodescription types are:

(1) elements as interlocking components (Fig. 10)(2) building surfaces as an array of joined elements (Fig. 13).

4.1. Elements

Elements are 2D objects used to build internal structures for3D building surfaces. Geometry for these 2D shapes is based onthe concept of building a coordinated device descriptionbetween CNC milling and laser cutting. Derived from physicaltesting, five sets of geometries from which most solid 3D shapescan be deconstructed are presented (Fig. 10). These elements aredivided into major components such as studs and sheathing,whereas minor shapes are used to build corners and joinbuilding surfaces. Parametric variation in studs allows forflexibility by bending in CAD (Fig. 10a). Tabs within the studgeometry allow for easy attachment of sheathing, whilevariables in the y direction allow for tolerance control betweenstuds and attached sheathing [t]. Thickness between sheathing iscontrolled by variable [s]. Horizontal forces acting on studframing is managed by bracing installed between each stud (Fig.10b). Last, interior and exterior sheathing is defined as a sheetembedded with any combination of three friction-basedattachment strategies (Fig. 10c). Slots with variables fortolerance are used to attach each sheet of sheathing to studs,biscuit attachments secure tension between sheets of sheathing,

ser-cut fabrication and (B) a full-scale mock-up of plywood at full-scale.

Fig. 10. Assortment of major and minor elements used to join straight and bent surfaces.


and box joinery at the edges is used for alignment at bends.Minor elements are used at corners for additional strength andallow for transitions at tight edges and corners (Fig. 10d and e).Combined major and minor elements are composed spatiallywith functional goals for waterproofing and structure. Assemblyof building elements is illustrated in Fig. 11, demonstratingcomponent hierarchies and behavior when walls meet to create aroof.

4.2. Building surfaces

This research considers wall, flooring, and roofing descrip-tions as building surfaces with variables for thickness andstructure. Surface bends and surface junctions are controlled by

Fig. 11. Outer sheathing is removed to display roof section studs demonstratin

variations in parameters of major and minor elements (Fig. 12).Variation in surface thickness [s] allows for increased strengthby adding material between inner and outer sheathing. A benefitin construction is that internal structure can be thinner at roofridges or valleys and thicker in areas of concentrated load.Surface strength is also controlled by the number of studs andbracing inside a surface [fh]. Strength is controlled by thefrequency of tabbed joints [fh] and the number of studs in asurface as well.

4.3. Surface types

Described here are surface types used as an intermediatedescription between smaller elements and a design description

g the resolution of a complex corner assembly with plywood components.

Fig. 12. Straight and bent building surfaces demonstrating possible variations in frequency of connections and sheathing size.


(Fig. 13). Variations in surface type are based on functions forinternal structure (studs) and the relationship of tab geometry thatattaches inner and outer sheathing to studs. Presented is anoverview of eight surface types as solid objects in column (a) andstructural geometries for studs in column (e).Of importance in thismatrix are the descriptions of geometric relationships betweenstuds and bracing and the attachment strategy for sheathing. Eachsolid surface is a parametric relationship between sheathing,studs, attachments, and material thickness. Rows 1–3 in column(a) are descriptions for surface-to-surface joinery of straightsections from a collection of smaller sections. Rows 4–8 aredescriptions of surface assemblies at corners, T's, and angles.Column (a) describes the initial shape as a solid model of varyingthickness s. Columns (b) and (c) illustrate edge connectionsbetween sheathing as biscuit joineries a–a for mating conditionsbetween sheathing, or as box joinery b–b at edges and dados (taband slot) that bond sheathing to studs c–c. Columns (d) and (e)express internal arrangements of studs with attachments.

5. Design manufacturing

Manufacturing a design is a multi-stage process that beginswith a single CSG model (design description) and ends with acollection of 2D elements for cutting. The three modeledexamples presented in this section illustrate the production of adesign between two machines from the same geometry; onemachine for design, one for construction. For this researchstudy, modeling commands were manually driven by keyboardin AutoCAD version 2004. To better understand the process,these stages are illustrated in Fig. 14:

Stage 1: The initial solid model is decomposed into sectionsas straight surfaces, bent surfaces, and joined surfaces.Panel numbering in Fig. 14 corresponds with rows for paneltypes in the taxonomy (Fig. 13).Stage 2: Integral attachments as mating parts are generatedbetween components and surface types (to illustrate theinternal components, outer sheathing is missing here).

Stage 3: 2D cutsheets are generated, reflecting componentsfrom the 3D construction model. Computer model compo-nents are labeled with a number in 3D and then translated toflattened positions for cutting. The number is scored intoeach component. Here, parts are organized for efficiency incutting by tightly nesting components on each sheet tominimize plywood waste.

5.1. Shelter design

To test the concept of precision joineries, productionspeed, and viability in the field of architecture, an integrateddigital fabrication process was applied to the design of asmall shelter. The building type is small enough to constructartifacts at desktop and full-scale and measure the resultswithin a reasonable amount of time. A modest 8′×10′ cabinwas designed with a pitched roof, windows for ventilation,and a door. Longer term expectations are that the sheltercould serve as emergency housing for people in remote ruralareas of the world. The house was elevated from the groundplane for construction access to the underside as well aswater drainage. A conventional house shape was selectedas the starting point in order to compare processing timeand methods against legacy shelter construction. The roofdid not have overhangs because they were found to be avery difficult detail to model and served as little more thanshading. Last, all external surfaces were smooth in prepara-tion for a waterproofing surface (shingles, paper, etc.). Atotal of three artifacts (two models and a building) wereproduced for the project.

5.2. Artifact A: desktop model

The first product was designed and constructed in fourworking days with a 50-watt laser cutter; approximately3 days was needed for modeling and 1 day for cutting andassembly. The model scale was 1″=1′0″; one-twelfth thesize of full-scale construction. Built of 484 parts this model

Fig. 13. Taxonomy of building surface types and connections.


Fig. 14. Three stages of transformation from a design description to descriptions for digital fabrication (state 3).


contained fewer parts than the full-scale shelter to follow.The model was laser cut from nine (18″×32″) sheets of 1/16″cardboard in approximately 4 h and assembled with gluein 6 h.

5.3. Artifact B: full-scale shelter

Next, a full-scale artifact was constructed over the course of1 month with a Techno Isle CNC 4′×8′ table router, EZ CAMsoftware, and 114 sheets of plywood (Fig. 15A). Base supportsfor Artifact Awere remodeled and reprocessed for Artifact B insearch of a cleaner façade aesthetic. The design change did notalter the overall design description, only the construction model(stage 2) and the cut sheets (stage 3). The physical change wasthat the number of supporting piers was reduced from six(Artifact A) to four (Artifact B). The second change was that thecut sheets used for Artifact B needed to reflect the change inscale from a desktop model built of few components to a full-

scale building created of many components. At full-scale, thegreater number of parts also meant a greater number of stockplywood sheets (4′×8′ sheets of 3/4″ plywood). A total of984 parts were cut with a 1/2″ router bit, of which 186 weresheathing, 165 studs, and 633 minor elements. The shelter wascut from a total of 101 sheets of plywood with 13 sheets forwaste and oversupply. After being cut, each component waspainted with waterproofing followed by 2 days of outdoordrying. On average, plywood sheets were cut in 20 min after10 min of file translation from AutoCAD format to EZCam (i.e.,30 min per sheet). Five to seven sheets of plywood componentswere cut per day. Total cutting time on the mill for the 114sheets of plywood was 55.4 h, not including file translations toCAM software and plywood setup. Assembly was in four stagesstarting with the base piers and flooring, walls, and roof. Withinthe month, parts were CNC-cut from plywood and waterproofedMonday through Thursday, and assembly took place on Fridays(four Fridays were needed for complete assembly). True

Fig. 15. Final construction of Artifact-B built of 984 individually numbered components after weather-proofing spray (A). Artifact C built of the same 984 componentsas a laser-cut model of 1/16″ cardboard stock (B).


assembly time was 4 working days (estimated time) with arubber mallet and crow bar for alignment.

5.4. Artifact C: desktop model

A second desktop model was produced of the same scale asthe first (1″=1′0″) with the same geometry used to build thefull-scale shelter (Artifact B) (Fig. 15B). As a scaled model,parts were difficult to assemble by hand alone; tweezers were

Fig. 16. Illustration of assembly behavior during construction of Artifacts

used for assembly. The purpose of Artifact C was to comparethe physical behavior and structural function of the componentsagainst the full-scale construction. This model was laser-cutfrom eight (18″×32″) sheets of cardboard and assembled withglue in 3 working days (estimated time), compared to the firstdesktop model cut and assembled in 1 day. Tolerance controlsfor laser cutting were not as accurate as tolerance controls forCNC mills. Unlike in the full-scale construction, integralattachments were used for component alignment in Artifact C.

B and C with center section deformation due to gravitational loads.


6. Results

6.1. Physical behavior and modeling

This research uncovered the complex relationship amongmodeling, machines, and materials, illustrating more thansimply manufacturing between scales. By working backwardafter the full-scale shelter (Artifact B) was built, similarphysical behaviors and complications in both desktop and full-scale artifacts (B and C) were discovered. First, the interlock-ing method tested in this research meant that framing andsheathing are erected together (Fig. 16). Both artifactsdemonstrated structurally weak framing without outer andinner sheathing. A key function in the method was that internalstuds were manufactured of many parts. All were less than 6′long, held together by friction only. Stud joinery was not self-supporting and needed the assembly of inner and outersheathing for rigidity. A second behavioral problem was thatthe assembly of small components led to problems associatedwith gravity in both Artifacts B and C. Because the framing(studs) and sheathing were assembled together (versusconventional methods to build framing first, sheathing second),gravity played a part in the attachment of the last few panels atthe roof. During assembly, starting from the ground plane,sagging occurred across the bottom surface from gravity loads(g). Compressive forces from outer studs moving inwardlimited the attachment of the last eight panels (four on eachside) (Fig. 16a). This was solved by placing temporarysupports under center sections during assembly of the full-scale artifact.

6.2. Limitations

The most outstanding dilemma in this production systemrelates to plywood as the material source and the limitations offlat stock. Material waste was a problem to control, both as asolid material in the form of plywood skeleton cutouts (114skeletons) and as a powder in the form of sawdust. Bothmaterials are difficult to recycle. CNC wood milling with a 1/2″drill bit meant that one square inch of material was reduced tosawdust for every four inches of cutting. Second, the shelter wasstructurally overengineered; studs were spaced too close (16″on center) with too many attachments between the sheathingand studs. It was discovered that a thinner material with fewerconnections could have achieved the same construction goal.Last, the greatest limitation of process was the conversion ofgeometries from design models to a model of components withembedded joineries. The time invested for repetitive modelingin the translation of solid objects to smaller objects to build acollection of interlocking components was extensive. Ingeneral, the shelter was modeled in approximately 4 workingdays.

7. Summary

There is high interest in the field of architecture in digitalfabrication for product manufacture at many scales. This

research demonstrates a novel application and process thatfacilitate concept-to-construction design manufacturing across avariety of machine scales. Described here is a method to linkdevices of all scales with one CAD description. It was alsodemonstrated that a small-scale design artifact can embodysimilar behaviors as full-scale construction if built from thesame geometric descriptions. This design and constructionmethod is paperless and ensures constructability from virtualand physical desktop models. This way of working opens thepossibility of models that better reflect function, structure, andbehavior as realistic constraints in design as they relate to thephysical world. Most importantly, research of this type enablesthe designer to consider downstream processes such materialsand manufacturing methods early in the design process.Generative tools can also consider these downstream processesas part of early phase design generation.

8. Contributions

System results illustrate that integration between two dig-ital fabrication devices (laser cutter and CNC router) fromthe same geometric data is possible. From this work, fournovel contributions are presented. First, this work offers anew way to structure design artifacts based on componentmanufacture with precision digitally based devices. Second,computer-controlled machinery supports component manu-facture with attachment mechanisms embedded within eachpart; no secondary fastening methods are needed for as-sembly. Third, a small house (shelter) could be built from onestack of one material (plywood) with four tools (computer,CNC mill, rubber mallet, and crowbar). Last, the experimentsdemonstrated a serious need for generative design systemsthat build geometry based on output with digital fabricationdevices.

Future studies will focus on the exploration of design toolsthat generate components with integral attachments as partof the generation process. The desired goal is to build designtools based on advanced understanding and physical reasoningwith new materials, generative modeling, and machinery. Last,an appropriate testing ground for generative tools for fabrica-tion is building product modeling for real-world construction.Full-scale construction will inform constraints for geometryand increase the relevance of associated data for productmodeling.

Acknowledgments

I would like to thank the students who have contributed tothe construction of artifacts for this study—Marcel Botha,Nicolas Rader, Victoria Lee, Diana Nee, and Maggy Nelson.Also, I thank The Center for Bits and Atoms for their generousfunding facilitated through support of NSF CCR-0122419.

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Lawrence Sass is an Assistant Professor at the Massachusetts Institute ofTechnology in Cambridge, Massachusetts, USA.

http://www.industrialorigami.com/home.cfm

http://laminadesign.com/index.html

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