Analyzing Joinery for Furniture Designed for Disassembly

Abstract

End-users can design personalized furnishing products using remote web-based CAD systems. However, if these designs fail to incorporate design for disassembly (DfD) principles, the furniture’s subsequent repair, reconfiguration, recycling, and disposal can be significantly hindered. To address this drawback, this study supports DfD, a strategy that enables the creation of easily repairable, reusable, and recyclable furniture to reduce waste and environmental impact. Consequently, this review aims to classify and evaluate available furniture joinery systems for their suitability within DfD frameworks, ultimately promoting their implementation within CAD environments. To this end, various solutions were evaluated, including traditional joints, dowel/biscuit, hammered, directly screwed, snap-on, expandable, and cam/bolt fasteners. Based on a literature review and practical observations, the analyzed joinery systems were categorized into non-disassemblable, conditionally disassemblable, and fully disassemblable categories. Only the fully disassemblable solutions effectively align with DfD principles. The study postulates a preference for expandable and cam/bolt fasteners in furniture designs, noting that although snap-on fasteners can potentially support DfD, this outcome is not always ensured. To guarantee that the designed furniture adheres to the DfD principles, the following eight furniture design guidelines were formulated: develop web-accessible disassembly instructions, prioritize access to fast-wearing components, prioritize modularity, standardize parts in modules, label components, enable independent component removal, use materials that withstand repeated disassembly, and employ fully disassemblable joints.

1. Introduction

1.1. The Transformative Role of Information Technology in the Furniture Industry

The furniture industry has undergone a transformation driven by information technology (IT) development [1]. For example, adopting CAD systems in the Turkish furniture industry has demonstrably shortened design processes, improved product quality, and reduced order fulfillment times by 57% [2]. Contemporary approaches to remote design by end-users of customized furniture leverage web-based applications featuring intuitive interfaces accessible to people with limited design expertise [3,4,5]. These platforms allow users to personalize various aspects of furniture, including dimensions, materials, finishes, and configurations [6], while realistic 3D models facilitate visualization, functional comparison, and access to pricing and availability [7]. This integrated design process seamlessly transitions to purchasing, and custom furniture production begins immediately upon order confirmation [8]. Manufacturing systems operating under a mass customization paradigm utilize these customer-generated designs, allowing efficient production on demand [9]. This collaborative methodology, variously termed “Do-It-Together” [10] or “Co-creation platforms” [11], represents a significant evolution in furniture design and production.

Integrating computer-aided design (CAD) with cloud-based platforms has fundamentally reshaped the furniture industry by improving design efficiency and streamlining production processes [12]. This involvement also has the potential to foster sustainability principles within the design process [13].

IT positively influences Furniture Life Cycle Management (

Table 1. Key aspects of IT in the furniture industry.

Aspect	Description	Key Literature Sources
Design and customization	Co-creating furniture with customers	[3,4,5]
Manufacturing	Facilitation of production processes	[14,15,16]
Service	Selling, delivering, using, maintaining, and disposing	[17,18,19]

). Contemporary cyber–physical furniture production systems exhibit both agility and cost-effectiveness. By way of illustration, the Internet of Things (IoT) enhances supply chain efficiency [14], and its synergistic integration with blockchain technology supports material transparency and traceability [15], facilitating real-time product lifecycle monitoring for sustainability compliance.

Although significant progress in IT has yielded numerous benefits, it has also introduced new challenges. For instance, while IT enables using a wider variety of furniture materials at lower prices, this complicates recycling and contributes to shorter product lifespans [20]. This shift towards a wider variety of cheaper materials exacerbates the negative environmental impact and opposes circular economy (CE) principles, which advocate for extending the life of existing products. Buyer-designed furniture presents principal problems in three key areas: overspecialized designs, inefficient material usage, and difficulties in end-of-life management.

1.2. Overspecialised Designs

The convenience of designing and ordering personalized furniture increases consumption. This is influenced by changes in trends, leading to more frequent replacement of “custom” items as tastes evolve. Although personalization initially forges an emotional connection, the ease of online design can increase the tendency to discard well-functioning furniture when desires change [21]. The limited resalability or donatability of highly personalized items leads to their faster disposal in landfills compared to generic pieces. This limited appeal in the second-hand market, which is characteristic of highly specific designs, further shortens their lifespan and increases waste generation [22]. Furthermore, customers without design expertise create flawed furniture designs that are functionally unsound or aesthetically unpleasant upon arrival, leading to returns, rework, and wasted materials and energy. The ease and lower perceived cost of designing online (even if the actual environmental cost is higher) foster a more disposable attitude towards furniture than long-lasting, carefully selected pieces [23]. Consequently, to re-establish furniture as a durable good [24], the furniture market must adopt strategies emphasizing longevity rather than cyclical obsolescence [25].

1.3. Inefficient Material Usage in Production and Shipping

Mass customization involves producing numerous unique items in small batches [26]. Although it theoretically promises material and energy efficiency by enabling on-demand production, compared with the potential overstock waste of large-scale standardized production, the actual implementation, with its unique setup for each design, leads to increased waste and decreased productivity. Moreover, the necessity of using diverse input raw materials creates complex and less efficient supply chains, because sourcing and transporting these varied, smaller material volumes elevates the carbon footprint [27]. Furthermore, direct shipment of individually customized items to numerous end users increases both packaging material per item and transportation emissions compared to bulk deliveries to retailers [28].

1.4. Difficulties in End-of-Life Management

The inherent material diversity, non-standardized joinery, and frequent lack of documentation in highly customized furniture significantly complicate and increase the cost of disassembly and recycling at the end of its lifecycle. The highly unique nature of these designs means that there are no standardized methods for disassembly. This hinders recycling efforts and leads to more landfill waste.

Although remote CAD systems for custom furniture offer appealing flexibility and personalization, they present environmental challenges related to fostering disposable consumer behavior and complexities in material use and end-of-life management. Addressing these issues requires the promotion of reparable and recyclable products. Consequently, enhancing the ease and accessibility of design-for-disassembly (DfD) solutions for consumers would mitigate the negative environmental implications.

DfD supports the creation of easily repaired, reused, or recycled products, reducing the negative environmental impact [29,30]. This approach is supported by modular furniture design, which allows interchangeable components to be updated or replaced [31,32]. To meet DfD requirements, furniture components or modules must be completely separable, allowing for multiple assembly and disassembly without affecting furniture properties. This outcome is achieved through the application of fully disassemblable joinery systems. In contrast, non-assemblable joinery systems, such as adhesive joints, prevent component disconnection and necessitate a destructive disassembly. Conditionally detachable systems allow disassembly, but this process is economically inefficient or leads to a decrease in the load capacity or reliability of the furniture after reassembly.

IoT devices can track the condition of furniture products, predict maintenance needs, and optimize repair and recycling processes [33]. Digital product passports (DPPs) are another innovative solution to promote CE practices in the furniture industry. These passports provide detailed information about the materials of furniture products, the production processes, and environmental impact, enabling consumers and businesses to make informed decisions about reuse and recycling [34].

In light of these possibilities, DfD enables multiple furniture repairs or, if repairs are not feasible, the recovery of components. Compared to non-disassemblable furniture, even when constructed from environmentally friendly materials, this strategy offers a significantly more sustainable design and production model. This study aims to classify and evaluate furniture joinery systems in terms of their compatibility with DfD principles while also promoting their implementation within web-based CAD environments.

2. Methods

A methodology used to evaluate furniture joinery techniques for design for disassembly (DfD) comprises three steps:

• Identification, classification, and DfD evaluation of current furniture joinery techniques. Reviewing industry publications, manuals, online resources, and scientific literature identified standard methods for joining furniture components. A novel classification framework was developed to categorize these techniques based on their varying suitability to DfD. The suitability of each identified joinery technique was then evaluated for DfD suitability through a combination of theoretical analysis of fastener design and function, practical observations of fastener behavior during assembly and disassembly (including destructiveness and ease), and publicly available data (including technical specifications and manufacturer data) supplemented by practical experimentation where possible.
• Generalization of results. The findings of the DfD evaluation of each furniture joinery technique were organized and presented in a table. This format allowed for a direct comparison of the characteristics of different joinery methods.
• Conclusions were formulated on the suitability of the analyzed joinery methods for disassembly.

Study Limitations

• This study is limited to evaluating commonly used furniture joinery techniques. Innovative solutions that are not yet widely widespread in technology may exhibit different characteristics.
• The practical evaluation was based on limited observations and may not cover all possible scenarios.

3. Results

3.1. Identification, Classification, and DfD Evaluation of the Furniture Joinery Systems

3.1.1. Identification and Classification of Furniture Joinery Systems

Furniture joinery systems can be categorized in various ways, reflecting their diverse applications. This study proposes a general classification subordinated to design for disassembly (DfD). As mentioned, furniture joinery techniques can be broadly categorized into non-disassemblable, conditionally disassemblable, and fully disassemblable. When disconnected, the first two groups require complete or partial destruction of the furniture components. Any attempt to disassemble a non-disassemblable joint destroys the furniture elements or modules. Disassembling conditionally disassemblable joints risks damaging furniture components or modules, and subsequent reassembly yields reduced or lost furniture utility upon reassembly. Conditionally disassemblable joints can also be defined as requiring a disassembly procedure that is too expensive or time-consuming.

From a DfD perspective, only entirely disassemblable joinery systems are interesting. While ready-to-assemble (RtA) furniture is designed for customer convenience, this does not automatically translate into ease of disassembly.

Given the significant structural diversity of furniture joints, a functional classification is warranted. This classification focuses on (a) the primary connecting element or mechanism (shape-based, fastener-based, specific interlocking features, specific anchoring features within furniture components) and (b) the required method of assembly (impact, driving, snapping, expansion, or tightening). Although some functional overlap exists in joinery (e.g., glue is often used in traditional joinery and with pins/biscuits), the dominant connecting method remains the key distinguishing factor for each category.

All types of furniture joinery systems can be classified into seven groups:

(1)

Traditional joinery systems encompass classic methods such as mortise and tenon, dovetail, and rabbet joints, which offer strong and durable connections but can be time-consuming during woodworking.

(2)

Pins/biscuits fasteners rely on a wooden “pin-shape” dowel inserted into holes made in connected furniture members; or thin, oval-shaped wooden biscuits placed in preformed slots. Both types of fasteners are standard in flat-pack furniture and cabinetry as auxiliary fasteners used with other mechanical fastener types or with glue.

(3)

Hammered refers to joints assembled using nails, staples, or other hammered fasteners. Relatively quick and straightforward in assembly, but they may not be as strong or aesthetically pleasing as other methods. They are not intended for disassembly. However, disassembly is possible.

(4)

Directly screwed connections are made by driving furniture screws directly through one component and into another. While offering fast and easy assembly with standard tools, these fasteners weaken the connection between furniture parts after repeated disassembly.

(5)

Snap-on-type fasteners employ interlocking plastic or metal features that engage during assembly (often with an audible “click”). Designed for quick, toolless assembly. Common in modern, flat-pack furniture, where ease of assembly is prioritized. These fasteners exhibit various designs, ranging from invisibility after assembly to requiring specialized disassembly tools or offering easy disassembly.

(6)

Expandable fasteners use mechanisms that expand within a pre-drilled hole or slot. This expansion creates a tight fit against the interior surfaces of the hole or slot, thus securing the fastener within the furniture component.

(7)

The bolt or cam fasteners employ threaded screw-nut fasteners or a cam lock–pin pair. These fasteners offer strong, adjustable connections, allowing for repeated assembly and disassembly. Common in RtA furniture and cabinetry.

These seven groups of furniture joinery systems, including many examples, are detailed in Appendix A,

Table A1. Comparison of furniture joinery systems categories based on their disassemblability.

Image	Name	Type of Furniture Joinery System	Disassemblability
			Non-Disassemblable	Conditionally Disassemblable	Fully Disassemblable
	Single trough mortise and tenon	Traditional	•
	Single-covered mortise and tenon		•
	Single bevel mortise and tenon		•
	Slant dovetail		•
	Semi-covered straight dovetail		•
	Straight framed		•
	Dowel	Pin, biscuit		•
	Elliptic dowel (Domino, Festool GmbH, Wendlingen a. N., Germany)			•
	Biscuit fastener (made of beechwood)			•
	Biscuit fastener (made of plastic, Bisco P-14, Lamello AG, Bubendorf, Switzerland)			•
	Self-tightening dowel (made of plastic, KNAPP®-Dowel, Knapp GmbH, Euratsfeld, Austria)			•
	Standard nail	Hammered	•
	Ring-shank nail		•
	Staple		•
	Standard small furniture screw	Directly screwed		•
	Self-drilling furniture screw			•
	Large furniture screw (requiring a pilot hole)			•
	Self-clamping two-part connector (Tenso P-14, Lamello AG, Bubendorf, Switzerland)	Snap-on (click)	•
	Shelving connector (Diwario P-18, Lamello AG, Bubendorf, Switzerland)				•
	“Invisible” clickable snap-on connector (Quick set, Knapp GmbH, Euratsfeld, Austria)				•
	“Invisible” snap-on connector (Normal 850, Effegibrevetti S.r.l., Milan, Italy)				•
	Slide-in connector (Chico, Knapp GmbH, Euratsfeld, Austria)				•
	“Invisible” sliding snap-on connector (OVVO V-0930, Santech Innovations, Paris, France)				•
	Click connector (Solo 32, Häfele SE & Co KG, Nagold, Germany)				•
	“Invisible” snap-on connector (Bone, SISO A/S, Skovlunde, Denmark)				•
	Expandable fastener (Ixconnect SC 8/25, Häfele SE & Co KG, Nagold, Germany)	Expandable	•
	Expandable fastener (Ixconnect SC 8/60, Häfele SE & Co KG, Nagold, Germany)				•
	Expandable fastener (Domino KV D8/50, Festool GmbH, Wendlingen a. N., Germany)				•
	Expandable fastener (BLU-8, CAR S.r.l, Padova, Italy)				•
	Expandable fastener (Quicklock expando, Titus Group, Prestons, Australia)				•
	Cam lock fastener, with inner rotating cam in plastic case, screwable directly in furniture member (Rafix, Häfele SE & Co KG: Nagold, Germany)			•
	Cam lock fastener, with inner rotating cam in metal case, screwable directly in furniture member			•
	Cam lock fastener, rotating in a socket, screwable directly in furniture member	Bolt or cam-based		•
	Cam lock fastener with insert nut				•
	Furniture bolt with nut				•
	Furniture bolt with claw-nut				•
	Detachable connector with lever mechanism (Clamex P-14, Lamello AG, Bubendorf, Switzerland)				•
	Hidden connector with magnetic drive (Invis Mx2, Lamello AG, Bubendorf, Switzerland)				•
	One-piece connector (Cabineo, Lamello AG, Bubendorf, Switzerland)			•
	One-piece connector (Elefant, Italiana Ferramenta S.r.l., Brugnera, Italy)				•
	Worktop connector (Quick, Italiana Ferramenta, S.r.l., Brugnera, Italy)				•
	Drawer connector (Face&edge, system 3, Titus Group, Prestons, Australia)			•
	Worktop connector (AVB 5, Hettich Group, Westphalia, Germany)				•
	Cam connector (42,0700, Blum GmbH, Herford, Germany)			•
	Bolt-metal muff connector (serie GN500, O.M.M)				•

.

3.1.2. DfD Evaluation of Furniture Joinery Techniques

Traditional wood joinery techniques capitalize on the inherent properties of wood. These techniques are well documented in Egyptian, Indian, Western European, Chinese, and Japanese traditions. Evidence from Egyptian and Indian furniture demonstrates the use of sophisticated joints, such as the dovetail, more than 5000 years ago, a practice that persisted in subsequent stylistic developments [35]. In 1757, the French writer and engineer Diderot, in his comprehensive encyclopedia, included over 90 detailed illustrations of traditional wood joint variants [36]. In particular, Japanese and Chinese traditions necessitated the development of hundreds of different types of joints due to the limited durability of nails and glues in the substantial temperature and humidity prevalent in much of Central and Southeast Asia. Furthermore, the highly resinous woods utilized in traditional Chinese furniture exhibit poor adhesion, even when subjected to solvent cleaning and modern adhesive application [37].

Traditional furniture joinery techniques can be classified as “shape-based joinery” because the strength and stability of the joint are based on the specific shapes and interlocking forms created in the parts of the jointed furniture. Examples are provided in

Table 2. Examples of traditional joinery used in furniture.

Image
Name	Bridle joint (or open mortise and tenon, or tongue and fork joint)	Mortise and tenon joint (a fully-encapsulated bridle joint)	Miter joint (both connected components have been beveled)
Reference	own study

.

Traditional joinery is used in contemporary industrial furniture and historically inspired pieces [38]. Due to the hygroscopic nature and dimensional instability, these shaped connections are rarely used in isolation. Instead, some use adhesives, while others combine with mechanical fasteners, such as dowels, screws, or staples [39]. Such combinations of different joining methods, including adhesive-based joints, hammered staples or driven fasteners, and traditional “shape-based” joining forms, can be termed hybrid or combined joinery systems. Figure 1 shows an example of a combination of a bridle joint, glue, and staples.

There are many possible combinations of joining techniques in hybrid joinery systems. However, as a general rule, these connections are inseparable, so they are generally unsuitable for disassembling. To address this limitation in specific applications, an alternative to relying solely on tight fits and adhesives involves incorporating removable and easily accessible fasteners, such as screws, bolts, or even carefully designed wooden wedges that can be extracted without causing damage to the joint [40]. Furthermore, future research and development should prioritize the creation of high-strength adhesives capable of being de-bonded through the application of specific triggers, such as heat or specific solvents, without compromising the components of the structural integrity of the wooden furniture. The successful development of such reversible adhesives would enable the controlled disassembly of traditionally glued joints.

Dowel, biscuit, or tongue-reinforced joints enhance connections between two furniture components by introducing an additional connecting element. Dowels, cylindrical fasteners made of wood or plastic, also serve as a standard structural reinforcement in traditional butt and miter joints [41] and supplement other fasteners in cabinetmaking. Functionally similar to dowels, biscuits are used primarily to join sheet materials like plywood, particleboard, and medium-density fiberboard [42]. However, solid wood offers a simpler fabrication alternative to mortise and tenon joints while maintaining comparable strength and facilitating component alignment for wider panels. In contrast, it is a linear element that creates a joint by being inserted into mortises in two adjoining furniture components. Regardless of the type of reinforcement, adhesive application is generally required for secure joining to dowels, biscuits, and tongues.

Table 3. Examples of pin/biscuit-type fasteners used in furniture.

Image
Name	Beech dowel	Beech biscuit (Domino, Festool GmbH, Wendlingen a.N., Germany)	Wood biscuit 20, Lamello AG, Bubendorf, Switzerland
References	photo M.S.	[43]	[44]

illustrates examples of dowels and biscuits.

Hammered furniture fasteners, such as nails and staples, are straightforward methods to join furniture components [45]. While quickly installed, including robotic montage, and suitable for many applications, they can cause splitting, are often visible, and may not provide the same structural integrity as more complex joinery techniques. Nails and staples are driven into the workpiece using a hammer or nail gun (staple gun). These fasteners secure materials through axial friction and lateral shear strength. Nails can feature a spiral or a ring shank to enhance withdrawal resistance.

Additionally, the tip of the nail, and occasionally the staple, is sometimes bent or clinched after insertion to prevent extraction. Consequently, nails or staples become challenging to remove due to limited gripping surfaces, bent ends, or ring shanks. They are generally considered less suitable for disassemblable furniture due to their potential for damage and difficulty in removal. The hammered fasteners used in furniture are exemplified in

Table 4. Examples of hammered fasteners used in furniture.

Image
Name	Nail	Ring-shank nail	Staple
Reference	own study

.

Screw-based furniture fasteners offer versatile furniture connections. Furniture screws range from small screws (up to 2.5 mm in diameter), through self-drilling screws that eliminate the need for pilot holes to screws requiring pre-drilled holes [46]. Small furniture screws, up to 2.5 mm in diameter, can be screwed directly into wood materials. Larger in-size self-drilling screws streamline factory assembly by simultaneously drilling and fastening. However, they require higher torque moments during a montage. The largest furniture screws, used with pilot holes, are preferred in RtA furniture due to their evident installation locations and ease of assembly with standard tools. They are also more suitable for disassemblable designs because they offer relative ease of removal and reinstallation. It is worth emphasizing, however, that repeated unscrewing and re-screwing result in a connection with significantly lower load-bearing capacity.

Table 5. Examples of screw-type furniture fasteners.

Image
Name	Small furniture screw	Self-drilling furniture screw	Largest furniture screw, requiring a pilot hole
Reference	Own study

provides examples of furniture screws.

The manufacturer usually installs snap-on-type fasteners in furniture components suitable for RtA furniture. These mostly innovative and patented fasteners employ interlocking mechanisms, such as snap-fits or spring-loaded catches, to connect mating furniture components [47]. They are particularly advantageous for modular furniture, allowing their efficient reconfiguration.

A primary advantage of snap-on-type fasteners is the ease of assembly without requiring tools like screwdrivers, wrenches, or drills. This is particularly beneficial for flat-pack furniture and DIY assembly. Assembly time is significantly reduced compared to other types of joinery techniques. The simple snap-on mechanism makes assembly intuitive, even for those with limited experience. Many snap-on systems are designed to be hidden within the furniture structure, resulting in a more aesthetically pleasing finish without visible hardware.

Table 6. Examples of snap-on-type furniture fasteners.

Image
Name	Tenso P-14, Lamello AG, Bubendorf, Switzerland	Diwario P-18, Lamello AG, Bubendorf, Switzerland	Normal 850, Effegibrevetti S.r.l., Milan, Italy
Reference	[44]	[44]	[48]

illustrates the selected click-based fasteners.

The disassembly of snap-on-type fasteners typically necessitates the controlled deflection of flexible locking elements to enable the separation of the connected furniture components. This action may be achievable manually, particularly in cases where the snap features are readily accessible. However, specific designs may require simple tools, such as a screwdriver or even purpose-adapted implements, as exemplified by using nylon zip-ties to maintain the disengaged state of multiple locking elements concurrently. Successful disassembly hinges on accurately identifying the specific release mechanism, applying force in the appropriate direction, and mitigating the risk of component failure due to excessive or misdirected force. Consequently, these fasteners cannot be universally categorized as entirely separable. Instead, they exhibit a spectrum of disassemblability, ranging from readily separable to conditionally separable (where disassembly may result in damage) and ultimately to completely non-separable configurations. They are generally well-suited for applications where frequent assembly and disassembly are expected. However, they may not be ideal for heavy-duty furniture structures due to their lower clamping forces than screw-based joinery systems. Table 6 illustrates the selected click-based fasteners.

Expandable furniture fasteners, similar to wall plugs, spread within a pre-drilled hole to create a connection [49,50]. These fasteners, typically made of plastic or metal, are inserted into pre-drilled holes. Then they are expanded, either mechanically or by inserting a screw, to anchor them within the surrounding material. Expansion fasteners exhibit superior performance in soft lignocellulosic materials compared to hard materials. They are suitable for furniture assembly where easy-to-assemble connections are required. Their ease of assembly is advantageous; however, they generally do not provide strong connections or the capacity for high assembly forces comparable to screws, bolts, or cams. Depending on the specific design, they are suitable for disassemblable applications [51]. Selected expandable furniture fasteners are shown in

Table 7. Examples of expandable furniture fasteners.

Image
Name	Domino KV D8/50, Festool GmbH, Wendlingen a. N., Germany	Ixconnect SC 8/60, Häfele SE & Co KG, Nagold, Germany	BLU-8/BLU-12, CAR S.r.l., Padova, Italy
References	[52]	[52]	[53]

.

The ease of disassembling furniture employing expandable fasteners is generally poor to moderate, depending on the specific design and materials. A significant challenge arises from the potential to damage the surrounding furniture material, notably particleboard or MDF, during disassembly. The inherent tight mechanical interlock created by the expansion mechanism resists reversal and frequently results in tearing the hole’s interior.

Moreover, the expandable fasteners, particularly plastic variants, are prone to damage under forceful removal, rendering them unusable for subsequent reassembly. Although some premium expandable fasteners are engineered for marginally easier removal, significant force is often still required. The structural integrity of the pre-drilled hole can be compromised by repeated assembly and disassembly, leading to less secure future connections, even with new fasteners. The furniture material also plays a crucial role in disassembly outcomes. Softer materials are more susceptible to damage, while denser hardwoods offer greater resistance than engineered wood [51]. While careful disassembly can reduce damage, it is often not intuitive.

In summary, despite their convenience for initial assembly, expandable furniture fasteners are designed with a primary emphasis on secure connection rather than ease of non-destructive disassembly. This design choice can negatively impact furniture lifespan by complicating repairs and hindering material recycling, thus warranting their classification as conditionally separable.

Bolt-based and cam-based furniture fasteners are widespread in furniture construction. Bolt-based fasteners, such as bolts with nuts or with threaded inserts, provide high-strength connections suitable for heavy-duty applications and disassemblable designs.

Cam-based fasteners, commonly used in RtA furniture, consist of two main components: a cam lock (a rotating disc with a slot) and a metal dowel (a cylindrical pin with a head or shoulder). The dowel is inserted into one furniture panel, and the cam lock is fitted into the adjacent panel, engaging with the dowel. Turning the cam lock with a screwdriver or Allen key pulls the panels together, creating a tight and secure joint.

Table 8. Examples of bolt-based and cam furniture fasteners.

Image
Name	Furniture bolt with nut	Furniture bolt with claw-nut	Invis Mx2, Lamello AG, Bubendorf, Switzerland
Sources	[52]	Own study	[44]
Image
Name	Worktop connector, Quick, Italiana Ferramenta S.r.l., Brugnera, Italy	Cam fastener	Face-edge, system 3, Titus Group, Prestons, Australia
Sources	[54]	Own study	[55]

illustrates the selected bolt-based and cam furniture fasteners.

Bolt-based and cam furniture fasteners offer significant advantages regarding disassemblability in furniture construction. Bolt-based fasteners, including bolts with nuts, threaded inserts, and connector bolts with barrel nuts or cross dowels, create a strong mechanical connection by clamping components together with threaded members. Disassembly is straightforward, requiring only a simple tool like a wrench or Allen key. The process is non-destructive to both the fastener and the surrounding furniture material. Therefore, bolt-based fasteners are highly reusable. They can be disassembled and reassembled multiple times without losing strength or integrity, making them suitable for furniture designed for repeated assembly and disassembly.

The threaded nature of bolts also allows for adjustability in the tightness of the joint, which can be beneficial in some uses.

Disassembly of cam fasteners involves simply rotating the cam lock in the opposite direction used for assembly. This releases the tension on the dowel, allowing the connected panels to be separated. The process is quick and requires minimal effort.

Cam fasteners are designed for multiple assembly and disassembly cycles, which is essential for the nature of DfD furniture. However, the plastic components of some cam locks can be susceptible to damage or wear over time or with excessive force, potentially limiting their long-term reusability compared to metal bolts.

Both bolt-based and cam fasteners offer significant advantages over permanent joinery methods like gluing when disassemblability is a key design requirement.

3.2. Generalization of Results

Table 9. Evaluation of furniture joinery systems based on DfD principles.

Type of Furniture Joinery System	Glue Required	Destructive Disassembly	Easy to Disassemble	Supporting the DfD
Traditional	Yes	Yes	No	No
Pin/biscuit	Yes	Yes	No	No
Hammered	No	Yes	No	No
Directly screwed	No	Yes	Yes	No
Snap-on	No	No	It depends on the design	Not always
Expandable	No	Partially yes	Yes	Partially yes
Bolt or cam	No	No	Yes	Yes

categorizes furniture component joinery systems by their disassemblability.

Table 9 highlights a divide between traditional and modern fasteners, with modern fasteners significantly better suited to DfD. Traditional joinery, pin/biscuit joints, hammered fasteners, and directly screwed fasteners generally result in destructive disassembly, meaning that the components are damaged during disassembly. Therefore, they are not suitable for DfD. Expandable and bolt/cam fasteners consistently support DfD, allowing non-destructive disassembly. Innovative click-based fasteners offer conditional DfD support. Their suitability depends on their specific design. Directly screwed fasteners, expandable fasteners, and bolt/cam fasteners can be considered easy to disassemble. However, expandable fasteners do not damage components during disassembly.

4. Discussion

The design principles for disassembly (DfD) were initially prominent in building design and manufacturing industrial products, especially electronics and automotive products [56]. Their application to furniture design has grown along with the increasing focus on circular economy principles.

Krzyżaniak and Smardzewski [57] postulate that an ideal furniture joint should exhibit simplicity in assembly, requiring no tools (a tool-less interlocking joinery system), be externally invisible, and provide proper stiffness and strength. Several companies have developed tool-less assembly systems for flat-pack furniture. For instance, Välinge Innovation offers Threespine^® technology [58]. These innovations enable assembling furniture components without needing tools, relying on specially designed interlocking fasteners. Some manufacturers are further streamlining this process by integrating fasteners directly into the furniture panels during production. This approach simplifies consumer assembly and contributes to a cleaner aesthetic by eliminating visible hardware. Furthermore, disassembly is designed to be equally straightforward, typically involving a reverse motion or a simple release mechanism.

Traditional cam lock and bolt-based furniture joinery systems are undergoing enhancements to improve durability and ease of use. These improvements include self-aligning mechanisms and more robust components designed to facilitate both assembly and, in some cases, disassembly, as well as to withstand multiple assembly and disassembly cycles without compromising furniture structural integrity.

Augmented Reality (AR) is being explored as an assistive technology for furniture assembly [59]. One application overlaps virtual assembly instructions onto physical furniture pieces via a smartphone interface. This approach guides users step-by-step, visually demonstrating the precise fit of components, thereby mitigating confusion and reducing assembly errors [60]. Furthermore, mobile applications enable users to scan QR codes on furniture components to access specific AR instructions. This real-time guidance enhances the clarity of complex assembly sequences, making them easier to understand and follow. This means that such techniques can also be used to dismantle furniture.

Automating furniture component assembly in manufacturing settings increasingly employs robots with advanced vision systems and grippers [27]. Notably, researchers at Nanyang Technological University in Singapore have developed a robot capable of assembling an IKEA chair in under 10 min [61]. Furthermore, ongoing research explores the potential of utilizing modular robots as “smart components” that can autonomously configure themselves into furniture structures. However, while this represents a potential future direction, the current literature indicates a contrasting trend toward furniture simplicity to reduce production costs and shorten the product lifecycle [27]. Consequently, the robotization of self-assembly and self-disassembly of furniture remains a theoretical idea for the foreseeable future.

The furniture industry generates significant waste due to short product lifespans, difficulty in repair, and the use of composite materials and disassemblable joining methods. However, the current state of the art offers ways to counteract these challenges:

• Current concepts, such as RtA modular furniture systems with standardized components [62], naturally align with DfD principles by inherently facilitating disassembly. This is because RtA prioritizes ease of assembly for end-users without engineering experience, acknowledging the need for assembly beyond the factory.
• Sociological research confirms the potential to increase furniture sustainability, revealing that younger consumers are willing to pay a premium for environmentally friendly options [63].
• CAD programs can enable DfD by offering essential tools for designing products that facilitate easy disassembly [64]. For example, 3D-PDNet, a graph-based learning approach, uses 3D CAD models to generate feasible disassembly sequences, significantly exceeding existing baseline methods [65]. This technology has been further enhanced with the development of Autodesk Fusion 360 plug-ins, which generate disassembly sequence animations [65].

From the end user’s perspective, furniture disassembly can range from a straightforward and convenient process to a frustrating endeavor [25]. The complexity of disassembly is influenced by many factors that designers and manufacturers must consider to truly embrace DfD principles and enhance the user experience and the sustainability of their products. Ideally, DfD furniture should eliminate the need for tools. End-users may not possess extensive toolkits, proprietary wrenches, or power tools, which immediately increases the barrier to disassembly. Furniture requiring only common tools like standard screwdrivers or basic wrenches is more user-friendly than furniture requiring specialized equipment to maintain. Proactive web-accessible instructions indicating the necessary tools are crucial [66]. Difficulty also arises when fasteners are hidden and not immediately apparent [67]. This statement contradicts the criteria articulated by Krzyżaniak and Smardzewski [57], who posit that ideal furniture connectors should be invisible. Such invisible fasteners inherently conflict with the fundamental assumptions of DfD.

Well-designed DfD furniture should have an intuitive disassembly process. Force should not be the primary method. The process should be accessible to a broad audience [68]. Designs with delicate interlocking members are prone to breakage during disassembly, especially if the user is unsure of the correct procedure. As mentioned earlier, hidden fasteners can lead to users applying force incorrectly, potentially damaging the furniture’s structure or finish.

A key goal of DfD, from the furniture user’s perspective, should be a quick and efficient disassembly process. Long or overly complicated procedures can discourage users from disassembling furniture for repair or recycling. Standardized and easily accessible fasteners contribute to a more efficient process. If disassembly is required for simple repairs or moving, a complex process can discourage users from extending the life of their furniture. At the end of the furniture’s life, ease of disassembly is crucial for separating materials for efficient recycling or proper disposal. A complex disassembly process removes the entire item, preventing the goals of the circular economy.

Crowther’s 1999 review [69] of DfD in construction yielded 14 tips for architects:

• Employ lightweight materials for easier component handling.
• Design component sizes to align with the planned handling methods.
• Design a separate structure and cladding for adaptable building envelopes.
• All components intended for disassembly should be readily accessible.
• Arrange components hierarchically according to their anticipated lifespan.
• Allow parallel disassembly, minimizing the sequential processes.
• Adopt a modular system that adheres to established industry standards.
• Utilize standardized tools and conventional technologies.
• Reduce the number of unique components and fastener types.
• Mechanical fastening methods are preferred over chemical adhesives.
• Identify all components referred to in the assembly and disassembly instructions.
• Develop an open design system that permits alternative design variants.
• Ensure components’ resistance to repeated assembly cycles.
• Facilitate disassembly at multiple scales, from individual components to structural units.

Synthesizing Crowther’s guidelines and the classification of furniture joinery systems proposed within this study, we derive eight guidelines for designers of disassemblable furniture:

• Provide both assembly and disassembly instructions, including why disassembly might be necessary (furniture reconfiguration, repair, end of use).
• Prioritize easy access to frequently maintained, repaired, or replaced components due to their shorter lifespan (such as upholstery, cushions, moving parts like reclining mechanisms, hinges, drawer slides, and casters).
• Design with modularity in mind.
• Design modules with a minimal variety of materials, with standard components and fasteners, enabling assembly and disassembly using common hand tools.
• Label all interchangeable modules and their components with numbers or QR codes for easy identification.
• Design furniture assembly procedures to enable the independent removal of components or sub-assemblies, moving beyond a strictly linear disassembly sequence.
• Choose durable component materials capable of withstanding repeated assembly and disassembly cycles without degrading structural integrity or aesthetic quality.
• Employ disassemblable mechanical fasteners (screws, bolts, clips, interlocking mechanisms) as the primary means of joining components, avoiding or minimizing the use of permanent adhesives.

Following these guidelines results in furniture with key DfD features: disassembly instructions to facilitate breakdown, replaceable wearable components for extended lifespan, modularity enabling diverse reconfigurations, standardized components for ease of supply, identifiable labeled components for simplified product renewal or recycling management, independent component removal to streamline the process, disassembly-resilient component materials to prevent unexpected damage, and fully disassemblable joint systems to further ease the entire procedure. Consequently, such furniture meets all DfD requirements.

The DfD approach is being implemented in the furniture industry. In the Swedish furniture industry, DfD has been applied to European Furniture Group (EFG) products, demonstrating how CAD tools can adapt products to the principles of the circular economy [70]. Similarly, the IKEA circular design strategy emphasizes the design for disassembly, recyclability, and durability, supported by CAD tools that facilitate modular design and end-of-life management [19].

The future of CAD in furniture design and manufacturing lies in advancing intelligent M and S technologies, enhancing data interoperability, and integrating AI for automated design processes [71]. This development supports more sophisticated CAD tools with real-time feedback for sustainable design decisions. Developing advisory systems within remote furniture design programs to promote sustainable furniture is a prominent trend. The classification and evaluation of furniture joinery systems from a DfD perspective directly contribute to this advancement.

5. Conclusions

This research examines furniture joinery techniques from a design for disassembly (DfD) perspective, a fundamental sustainability strategy applied to customized furniture. Connection systems that enable efficient and non-destructive disassembly are identified as the most efficient for furniture design. The general conclusions of the study are as follows:

• Traditional joinery methods (shape, pin/biscuit, hammered) are generally incompatible with DfD, while modern fasteners (particularly bolt/cam-based) are well-suited.
• For DfD applications, snap-on-type fasteners must be engineered to enable non-destructive and straightforward disassembly. While specific designs facilitate this readily, others do not.
• Easy-to-assemble fasteners, such as screws, expandable, bolt, or cam types, are standard in ready-to-assemble (RtA) furniture. Since RtA furniture is designed for easy assembly after transportation and sometimes for reconfiguration through disassembly, the principle of ensuring complete disassemblability appears to be a logical extension.
• Although cost-effectiveness is a primary concern in furniture joinery standards, fully disassemblable systems do not inherently incur higher costs compared to non-decoupled alternatives. Importantly, by prioritizing fasteners that support DfD, furniture manufacturers can strategically position themselves within a circular economy, enabling the profitable recovery and reuse of furniture components and products.
• For a design to adhere to DfD principles, the following eight features are essential: attached disassembly instructions; prioritized access to fast-wearing components; furniture modularity; standardized parts within modules; labeled parts; the ability for independent component removal; the use of disassembly-resilient component materials; and the exclusive employment of fully disassemblable joint systems.

The conclusions of this study are of practical value as they directly address the need to bridge the gap between traditional furniture design and the increasingly critical imperative of sustainable circular economy models. Specifically, the findings indicate that a sensible selection of furniture joinery systems offers tangible benefits for adhering to circular economy principles.

6. Patents

Two patent applications were created based on this article’s assumptions and state-of-the-art analysis:

Stańczyk, K.; Sydor, M. Łącznik do łączenia dwóch elementów płytowych/Fastener for connecting two board elements. Patent Application No. P.448646. Polish Patent Office, filed on 22 May 2024, assignee: Poznań University of Life Sciences, Poznań, Poland.

Stańczyk, K.; Sydor, M. Łącznik do wykonywania połączeń elementów płytowych/Fastener for making connections between board elements. Patent Application No. P.450082. Polish Patent Office, filed on 21 October 2024, assignee: Firma handlowa Lotar1 Jarosław Wójcik, Małgorzata Wójcik Sp.J., Rydlówka, Poland.