Non-Modular Building Systems

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Part of our director of Open Source Manufacturing Tools, a draft selection from Eric Hunting.

Non-Modular Building Systems:

Traditional Carpentry - Supported by the vast majority of off-the-shelf tools and contemporary DIY literature, traditional wood carpentry remains the most common set of techniques used for independent manufacture in the western world. However, it is also entirely limited to wood and engineered wood materials, severely limiting the range of practical artifacts it is capable of producing. Though decorative techniques can be extremely elaborate, wooden assemblies are commonly based on fitted box panel and box frame structures using tab, biscuit, mortice and tendon, dovetail, small nail and screw, small metal fitting, glue, and slot/key joinery at the small scale and post and beam, stressed skin, and 'light wood' or 'platform' framing using mortice and tendon, nail, and bolt joiner at the large scale. More sophisticated techniques include the use of space frames and formed/bent wood and laminates. Without the benefits of modularity, traditional carpentry tends to demand high skill levels and labor to compete in quality with factory products and can be wasteful of an increasingly unsustainable resource, particularly at large scales. Sustainability has improved to a small degree with the increased use of engineered lumber materials using formerly waste material, though sometimes at the compromise of latent toxicity from chemicals. The introduction of materials like wheatboard and new bamboo and other more renewable lumber alternatives offers some hope for improving this further, though most of these new materials remain beyond the means of small scale production and unavailable from typical lumber sources.

Welded Profile Spaceframe Systems - Welded profile space frame systems employ tubular alloy profiles in typically round or square profile shapes as the basis of a structure assembled with welded joints. They usually employ either rectilinear box frames -typical of housing uses and machine structures/enclosures, or triangulated trusses but can be elaborated into complex free-form shapes through the custom-bending of frame members, as demonstrated by the space frame chassis of some vehicles. Though not modular in themselves due to their welded connections and often non-regular topology, when standardized over a whole form they can serve very well as the foundation for modular retrofit components, as also well demonstrated by their vehicle applications. Indeed, this is the most-likely basis of the design and production of larger open source artifacts such as automobiles, given that the technology offers superior performance characteristics to the more conventional pressed steel welded unibody construction of factory-produced automobiles (hence its common use in race cars and military vehicles) while still being suited to the scale of production of a very small machine shop. Welded profile spaceframe structures based on structural steel profiles have also been a mainstay for housing applications among Modernist architects and have proven very effective. Such housing has often seen an attempt by designers to modularize their structures through standardized component dimensions and the use of large modular sectional frames that are partly prefabricated and partly site assembled.

Composite Shells - Composites shells are rigid shell structures which are made of a combination of resins and fiber reinforcement, commonly in the forms of fiberglass, polyester, and carbon fiber. Though employed in such advanced applications as aircraft structures, the basic techniques used may have their origins in the simple techniques of papier-mache; the method of making sculptures from layers of glue/starch-soaked paper strips. Several techniques are common; formed, foam-core, free-form, and wound. Formed composite shells are made by creating removable forms, usually of plywood or corrugated cardboard, in an either concave or convex shape to which resin-soaked mats or tape are applied in multiple layers to build up a rigid shell finished in a smooth coating of resin. Small structures are usually self-rigid but larger more complex shapes can often be reinforced by bonding in flat or tubular spars of pre-made composite to create a monocoque or stressed skin structure. Large structures are sometimes produced in sections which are mechanically assembled along facing edge spars before being 'knit' together to seal their seams. This allows for the build-up of large structures by using assemblages of thin unfinished sectional shells as permanent forms for thicker shells built-up on top of them. Foam core shells are made by carving blocks of polyurethane or polystyrene foam into the desired shape then applying the resin-soaked fiber layers leaving the foam permanently in place. This technique is commonly employed in the creation of surf boards and pontoon hulls. The technique allows for intricate shapes based on the density of foam used but is best suited to structures that are intended to be monolithic in character, as surf boards are. Double-sided finished shell structures are possible based on using hollow foam structures sculpted to shape on both exterior and interior surfaces. Free-form shells are based on the use of wire mesh as a sacrificial form to construct a desired shape which is then covered in layers of resin-soaked fiber. This technique allows for very intricately detailed sculptural forms over very large areas. Wound shells are made by mounting a form structure on a large axial spindle which allows it to be rotated whole as fiber is applied as a continuous string or tape in a continuous semi-automated process. Rigs are sometimes designed to allow windings in multiple directions for each layer or wound layers may alternate with matted layers. This most sophisticated composite shell technique is used almost exclusively by the aerospace industry to make composite carbon fiber aircraft structures and fuel tanks but has also been used for the creation of super-pressure pneumatic tanks used for compressed air powered vehicles and energy storage systems.

Monocoque and Stressed Skin Structures - Typically associated with ships and aircraft, this class of structures is also common to structures using composite shell construction and and is characterized by the use of skin materials tensioned by their own stiffness and/or the use of an internal framework. In a stressed skin system, or semi-monocoque, the skin material may have no stiffness and rely entirely on a frame structure combining spars with perpendicular stringers or triangulated struts. This internal frame is intended to translate internal and external loads into tension on the skin material. In a true monocoque the stiffness of the skin material alone, usually employing rounded shapes, is relied on for strength but may be supplemented by spars, whose chief job is to communicate internal loads to the exterior shell without concentrating them on any one skin point. Favored for their strength-to-weight performance, these structures can be some of the most complex to build combining many techniques and using many different materials. Key among the engineering challenges is the means to interface skin materials of limited dimensions. Limited by the practical dimensions of lumber, early ships employed complex mortice and tendon system to join relatively thin planks into large area shells that behaved as though they were monolithic. Of course, they were never entirely waterproof. Later techniques based on lamination of wood, the gluing of fabrics, and riveting and welding of alloys emerged. Today, continuous welding of alloys and laminate polymer/fiber composites are common. True monocoque structures represent the highest challenge for casual makers owing to the very large skill sets and precision they require. Stressed skin systems are much less challenging in this respect and can be produced with fairly simple materials.

Pressed Alloy Shell Structures - A derivative of monocoque structures, this class of structures is typified by the humble soup can and the welded steel unibody construction as commonly employed in automobile manufacture. Essentially, curved or corrugated shapes are pressed out of flat sheet alloy stock and roll-seam-joined or welded together into a self-rigid structure. Rigidity is dependent largely on the curving forms employed in the component shapes, but simple sharp-edged forms are possible where flat surface areas are minimal. Ubiquitous in the production of many Industrial Age products prior to the introduction of plastics, the technology remains common for automobiles and large appliances and is often exploited by manufacturers as a means to control competition by industry standardization of production equipment of extreme scale and capital overhead. This generally imposes a great barrier to Maker use of this form of structure except at scale suited to parts fabrication by very small hydraulic presses or hammer-forming of pieces by hand.

Cast/Milled Block/Chassis Structures - Structures of this class are based on the use of a block or frame chassis structure which is cast whole or milled from a single or small set of blocks and used as the foundation for attachment of other components to build-up an overall structure. Casting and milling are, of course, fabrication techniques, not building methods, but when a cast or milled structured is used as the foundation of an assemblage of parts, it becomes a building system, sometimes suited to modularization. As with many other non-modular building methods, this type of structures has generally been very limited in its potential use by Makers owing to the large scales and high skill overhead of the base fabrication methods needed for its parts. But at small scales one can function within the limits of digital CNC which makes this a more practical option. Commonly based on alloys, this type of structure can employ any material that is millable or castable and can support the attachment of components by bolts, welding, or adhesives.

Masonry Structures - This class of structures falls into three basic categories; monolithic structures usually relying on bi-state plastic materials like concretes relying on formwork to control form during state transition of the material, stacked or rubble structures which rely on found materials like stones with human skill relied on to control form through selection, and block systems which rely on the regular geometry of prefabricated blocks to control form. Many forms of hybridization exist between these three basic categories as well as the use of conventional carpentry. Originating with the use of hand-formed clay/mud structures, this represents one of the oldest of all known building technologies, with a legacy suggested at over 10,000 years old and strongly associated with the development of the related technologies of pottery fabrication and ceramics. However, it is also a technology that has long resisted improvement of its basic limitation; high labor overhead. It is also a technology generally limited to architectural applications, though in some cases can be employed in the creation of furniture, sculpture, low-tech appliances like wood stoves, and some stationary machines like kilns, furnaces, stationary engines and pumps, and the like. For most of history masonry construction has been dominated by the materials of clay-bearing earth and stone with some use of primitive geopolymers and fired bricks in Roman times. With industrialization came expanded use of fired bricks and the emergence of portland cement based concretes but earth still dominated in much of the world. In modern times fired brick has been largely eliminated as economically impractical and concrete and prefabricated concrete block have been dominant but accompanied by a great diversity of other technologies and materials including extruded clay panels and blocks, gypsum block and plank, engineered stone, glass block, advanced geopolymers, and in-situ machine extruded masonry. Modular slip-formed and factory-precast concrete remain the current leaders in low-labor technology but may soon find competition from in-situ extrusion technologies offering the prospects of 'fabbing' masonry structures by computer control. Since the latter part of the 20th century earthen construction has seen a revival of use in developed countries based on its environmental characteristics, yet has seen little improvement in labor overhead beyond the use of hydraulically compressed earth block. earth bag/superadobe, and slip-formed cast earth techniques.

Ferro-cement - Most commonly employed in the creation of concrete sculptures and free-form organic architecture, ferro-cement was originally invented in the early 20th century as a means to make yacht hulls from cement. The basic technique involves the use of a wire mesh or mesh lathing (as used in plasterwork) as foundation for an application of hand-applied or sprayed concrete, known commonly as 'shotcrete' because it's 'shot' from a hose under pressure using a peristaltic concrete pump or by compressed air using a plaster spraying device known as a tirolessa. The technique produces very thin but strong cement shell structures and, though sometimes used with tension frames to create a kind of tilt-up masonry panel, it is most commonly used to create domes, spheres, hypoid, conic shells shapes or large flowing sculptural shapes based on the use of free-form wire mesh, sometimes employing double-shell structures with a core of pumicecrete or polymer foam as insulation. Recently, manufacturers have introduced prefabricated ferro-cement foundation panels combining wire mesh over and through a polymer foam core which can be used flat or cut and bent to some degree into more fluid shapes. (see Ferro-cement is the mainstay of the Free-Form Organic school of architecture, whose buildings feature elaborate complexes of non-euclidean shapes with formed-in-place furnishings and which is often regarded as the closest current analogy to architecture likely to result with the advent of advanced nanotechnology.

Pneumatic Structures - This class of structure is a derivative of stressed skin or tension structures based on non-rigid material that rely on internal pressure to provide them with rigidity. They are typically formed of welded/glued panels of polymer or polymer-composite materials fashioned so as to hold a relatively high internal pressure. Commonly seen in pool toys and inflatable novelty furniture, this technology is suited to very serious tasks such as the construction of airships, winged aircraft, and very large span building enclosures. With new membrane materials such as mylar, kevlar, tefzel, and in the future nanomembranes extremely high permanent internal pressures are now possible, allowing this fairly simple technology to produce very strong structures as rigid and solid as any more conventional material. Though still experimental, such materials have been used as wall and window panels in buildings and for struts in space frame structures.

Tension Structures - Similar to stressed skin systems, tension structures are typified by tensioning of a non-rigid material by perimeter edge anchoring to various forms of internal or external framework, anchor points, or piers. Though most commonly used as the basis of light enclosures -sometimes of enormous areas- they can also be used as the basis of tensegrity structures like bicycle wheels and geodesic tents and used as the basis of various machines and hybrid transforming structures such as Hoberman structures. One of the few forms of non-modular structures that are extremely well suited to Maker exploration.

Textile Structures - Commonly seen in the creation of clothing, furniture upholstery, toys, and the like this class of structure has evolved to include a complex assortment of hybrids where sewn and welded textiles are rigidized through internal filler material and frameworks that sometimes border on tension structure or stressed skin systems. Most exploration of this form of structure has been limited to furniture and toy design and 'soft sculpture' art but with the advent of sophisticated variable density structural foam polymers many new possibilities are emerging and we may soon see this form of structure commonly used in a growing variety of artifacts including such applications as personal housing on orbit, relief shelters, and vehicle bodies.

More Information

  1. Modular Building Systems
  2. Open Source Manufacturing Tools