Joints and Connections
Exploring modes of connectivity
The techniques examined in this study explore different modes of connecting two parts of a 3D print. The focus is on documenting interlocking approaches to identify the most effective technique for architectural applications.
What are 3D printed Joints and Snap Fits?
In 3D printing, joints refer to design features incorporated into a model that allow parts to be interconnected without relying on external adhesives - such as glue.
Among the various types of joints utilised in 3D printing, Snap Fit joints in particular offer a very simple method for connecting two components of a 3D print.
Types of 3D printed Snap Joints
Regardless of their specific type, all snap joints share a common principle around their assembly process: a protruding element of one component, e.g., a hook, stud or bead is deflected briefly during the joining operation and engaged with a recess (also known as the undercut) while attaching.
The following six examples have been selected in correlation to the three main types of Snap Fit techniques:
Cantilever
Spherical
Other: Offset/Cylindrical
1. Cantilever Snap Fit – Exposed
Functioning like a hook, the Cantilever Snap Fit securely clips onto a separate component of the 3D print. Common for its versatility, this type of joint is beneficial for enclosed areas, as both the joint and its counterpart are visible and accessible.
Strength | Robust and suitable for various types of top covers. |
Weakness | The joint becomes rigid when the hook is in an L-shape, limiting its movement in most situations. |
Tolerance | Open to being customized. |
Considerations | The width of the hook(s) plays a crucial role in determining the joint's functionality. Cantilever snap-fits can vary in flexibility based on their shape. To increase flexibility, it is advisable to shape the hook into a U-shape. |
2. Cantilever Snap Fit – Pocket
The Cantilever Snap - Pocket, like the exposed cantilever snap, is a snap fit technique that involves inserting a protrusion (resembling a hook or clamp) into a specifically cut out or engraved opening. This joint, hidden from view, provides enhanced strength by increasing the depth and dimensions of the hook.
To remove the joint the protrusion can be rotated or clenched at both ends, depending on the depth of the hooks.
Strength | Robust, Durable. |
Weakness | Highly noticeable, an in most cases, becomes fixed and difficult to remove. |
Tolerance | The design can be customised according to designs parameters. |
Considerations | The strength of the joint is determined by the depth of the internal openings. Recommend depth of 2mm is advisable. |
3. Separable Snap Fit
Incorporating ‘pins’ as a means of alignment, this technique involves utilizing any form of ‘pins’ to accurately align different parts of a model. These pins can be attached to one of the 3D printed components or inserted independently into both parts of the prints.
Keeping in mind the tolerance of 0.5mm to ensure a proper fit and alignment.
Strength | Fast method to align and join components. |
Weakness | Prone to being less robust. |
Tolerance | Model utilises a tolerance of 0.4mm. |
Considerations | It is recommended to experiment with different tolerances. For stronger and more durable joints, a tolerance range of 0.15-0.2 should be considered. If the components are intended to be easily disassembled and reassembled, a tolerance of 0.2mm-0.4mm would be suitable. |
4. Screw – Single Direction
Replicating the screw, the 3D printed screw is sturdiest out of all the six joinery techniques. Toughest to implement in a conventional architectural model - this type of joinery works in a one-way direction and could be considered for a more, abstracted way of representing your design.
This type of external joinery requires both the components to be modelled in a specific angle and would require at least ‘coin size’ opening and extrusion.
Strength | Highly Robust, Structal and Operable. |
Weakness | Restricted to visible dimensions, strictly used for round-shaped components. |
Tolerance | Experimentation is needed to determine the optimal tolerance for this joint. |
Considerations | This joint technique is suitable for objects with components that require frequent opening. It functions similarly to a screw, providing a strong and robust connection while allowing for movement. |
5. Spherical - Ball and Socket
As one of the most versatile and adaptive joinery techniques, the Ball-and-Socket joinery allows movement between two components. Snapping into a socket, the joint allows the freedom in rotation of multiple directions.
Strength | Multi-axis motion. The joint can be either detachable, difficult to disassemble or inseparable. |
Weakness | Highly visible, serving more as an additional design element than a hidden joint. |
Tolerance | The optimal tolerance depends on the dimensions of the bead and the return angle. |
Considerations | If a rotation of up to 180 degrees is required, this joint technique should be considered. |
6. “Offset”
Instead of snapping into place, the 'Offset' technique uses the (offset} Rhino command to simply align two components of a 3D print. Take note that a minimum tolerance of 2mm is required.
Strength | Easily incorporated into the design process, providing a fast way to align two components. |
Weakness | Highly adjustable, requiring additional measures to secure the desired position. |
Tolerance | Minimum offset of 0.5mm is advisable. |
Considerations | This connection technique acts as a point of alignment rather than a full joining of elements. It is important to note that the technique aligns parts rather than providing a strong connection between them. |
Key Considerations
Splitting
Splitting your geometry can be accomplished using various modelling software options. In this investigation, the focus was exclusively on Rhino software. Once the modelling stage is complete, the responsibility falls on the user to determine the method and purpose of splitting the model.
Material
Understanding what material to use for the joining of two components is crucial. While both (PLA) and (TPU) are popular 3D printing filaments, they are used for different applications – taking note that (PLA), even though being the more affordable option, shows limitations in flexibility when compared to the elasticity of (TPU).
Alignment and Tolerances
When adopting a model that involves the integration of one or more components, it is crucial to carefully assess the alignment and tolerances of the chosen components. The appropriate spacing between elements plays a decisive role in determining whether parts of your model will fit together - harmoniously.
It is important to remember that each joinery technique serves as a method to connect segments of your 3D print. The decision regarding the desired attributes, such as strength, flexibility, aesthetics, and or a clean finish (either sanded or not), rests with the individual.
Finishes
Make sure to consider that some joinery techniques, like the Cantilever Snap Fits joints, are snap fits - designed to remain fixed without being easily dislodged. If seeking operability, consider less permanent joinery techniques.
If a less noticeable joinery finish is desired, it is advisable to explore the concept of the "offset" joint or consider incorporating separate pins or dowels.
Future Considerations
Remember that each joinery technique serves as a method to connect segments of your 3D print. The decision regarding the desired attributes, such as strength, flexibility, aesthetics, and or a clean finish rests with the individual.
For future explorations, one could consider the Ball-and-Socket connection as an interesting technique worth experimenting with and for joinery that seeks to bridge two components, and still have flexibility in rotation, (TPU) is advisable.
Take note of, that Snap fits can also be damaged due to incorrect handling. And are not optimal if requiring repeated assembly operations.
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