Maya Ellison
Designing a plastic hinge-pin is a complex process that requires careful consideration of various factors. Plastic is a reasonably weak material, and hinges require specific design elements to ensure they bend without flexing and can hold a substantial amount of weight. The hinge-pin, in particular, must be strong, especially at its attachment points, and the barrel should be stronger in the centre. This design will ensure the hinge is stronger than a constant diameter axis and barrel with the same build volume. To achieve this, the pin's diameter must be carefully calculated, and the material must be stiff and strong.
| Characteristics | Values |
|---|---|
| Type of pin | Solid pin, coiled-spring pin, cotter pin |
| Hinge type | Free-fit, Friction-fit |
| Material | Plastic, steel, tubing |
| Design | Living hinge, flush rivet |
| Installation | Driven in from each side, threaded hinge pin |
| Size | 40x40mm, scalable |
| Printing material | PLA, PETG, ABS, Nylon |
| Strength | Stronger at certain points, constant strength throughout |
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What You'll Learn
Consider using a coiled-spring pin for lower costs and higher performance
When designing a plastic hinge, consider using a coiled-spring pin for lower costs and higher performance. Coiled-spring pins are a leading use case for hinges as they match or exceed the performance of solid pins while reducing costs. They are functional springs, formed from a strip of material rolled into coils, typically wound 2.25 times. The outer diameter of the pin should be larger than the diameter of the hole it is installed in, creating friction.
Coiled-spring pins can be used in both free-fit and friction-fit hinges. In a free-fit hinge, the pin is held tightly in one or two retaining holes, with the outside of the pin passing through a larger hole in the opposing part. The coiled-spring pin can be designed to have little to no friction or drag when the latch or handle rotates. In a friction-fit hinge, all holes should be sized identically, and the coiled-spring pin can be designed to have varying levels of resistance, from a slight drag to a fixed position.
Coiled-spring pins come in light, standard, and heavy-duty varieties, referring to the thickness of the material used. Light-duty pins are flexible and work well in plastic hinges, while heavy-duty pins can cause stress in lighter materials. Designers should consider the recovery and retention of the pin in free-fit applications, as well as the "free span" of the pin, or the distance it passes through a free-fit component. For better load distribution, the tight fit of the coiled pin should be in the outer members of the hinge.
Coiled-spring pins offer several benefits over solid pins. They simplify the design process as they do not require accommodating misalignment between holes to ensure friction. They can also absorb shock and vibration, resulting in fewer maintenance issues and a longer assembly life. Additionally, they conform to a wide range of hole tolerances and do not damage the plastic during insertion.
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Ensure the hinge bends without flex and can hold weight
Plastic is not the ideal material for a hinge-pin, as it is reasonably weak and requires oversized dimensions to achieve stiffness and strength. However, if you are set on using plastic, there are some things you can do to ensure the hinge bends without flex and can hold weight.
Firstly, it is important to consider the design of the hinge. A coiled-spring pin can be used to lower costs and extend the life of the hinge. The type of fit is also important. A friction-fit hinge has resistance, which can vary from a slight drag to a level sufficient to hold components in a fixed position. This type of hinge is well-suited for holding weight. The minimum thickness of the outer members should be 1 to 1.5 times the diameter of the pin.
Secondly, the shaft of the hinge needs to be strong, especially at its attachment points. The barrel will be stronger at the centre, so the overall hinge will be stronger than a constant diameter axis and barrel in the same build volume. A fifty-fifty support-hinge ratio is a good option, with the profile of the hinge getting larger smoothly until the barrel area.
Finally, the material and printing process are important considerations. It is recommended to use PLA or PETG as the printing material, as ABS and Nylon bend too easily. The hinge should be printed vertically to get a smooth motion.
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Design a free-fit hinge with little to no friction
To design a free-fit hinge with little to no friction, you can use a coiled spring pin. This type of hinge allows components to swing freely and independently of one another. The amount of friction in a free-fit hinge can be adjusted by changing the pin diameter or the size of the holes the pin goes through.
When designing a plastic hinge-pin with little to no friction, there are several factors to consider. Firstly, the size and placement of the circular nubs or protrusions that act as the rotation point are crucial. They should be large enough to provide stability and prevent unwanted movement, but not so large that they cause friction or binding. Proper alignment between the circular nubs and the corresponding recesses in the other part is also essential for a smooth and secure locking mechanism.
Another variation of the pin hinge design involves using plastic as the lever or pin that locks the hinge. The plastic lever is designed with a specific shape or cutout that engages with a corresponding feature on the opposite part. The locking mechanism should be secure when engaged and easy to release when desired. The flexibility of the plastic material used for the lever and pin is an important factor in ensuring smooth operation and durability.
When designing a free-fit hinge, the first step is to establish the maximum hole size in the retaining component for a tight fit. The coiled pin is then inserted, and the free diameter of the pin at the centre of the span is measured. A clearance factor is added to determine the minimum diameter of the free hole, usually 0.001 inches (0.02 mm). The required production tolerance is then added to assign the maximum diameter of the free hole.
For a free-fit hinge, the preinstalled diameter of the coiled pin is less important because it is the smallest holes in the handle that determine the final pin diameter. Designers must consider recovery and retention in free-fit applications, which depend on the diameter of the retaining hole and the "free span" of the pin. The "free span" refers to the distance a pin passes through a free-fit component. As the free span increases, the pin diameter will also increase as it recovers its preinstalled diameter.
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Bevel the openings of a tube for a better purchase
Plastic is a reasonably weak material, and you need to oversize the dimensions to get some stiffness and strength. Beveling is a process where an angle is formed between the edge end of a tube and a plane perpendicular to the surface. Beveling a tube is most frequently used to prepare its ends for welding. The process of beveling is also known as pipe chamfering, pipe end working, pipe end preparation, and pipe prepping. The bevel angle can be any angle except 45 or 90 degrees. The standard bevel angle for welding is 37.5 degrees.
There are several methods to bevel a tube, including using a portable or stationary beveling machine, a hand grinder, or a plasma or torch cutter. Portable beveling machines are notably safer and more time-efficient than hand grinders, but they are inadequate for high production requirements. Stationary beveling machines provide the most options and flexibility for beveling. They can create almost all kinds of pipe bevel shapes and are designed to meet high production requirements in a safe working environment. Additionally, they are easy to integrate with automated production lines, so an operator is not always needed.
When beveling a tube, it is important to consider factors such as the portability/mobility requirements, the specifications and quality of the bevel, and the type of pipe or tube material being used. For example, beveling methods may vary depending on the material of the tube. The speed of the beveling machine is also crucial, as a quick process can improve productivity and efficiency.
In the context of designing a plastic hinge-pin, beveling the openings of a tube can provide a better purchase by creating a smooth transition between the edge of the tube and the perpendicular surface. This can facilitate easier assembly and improve the overall aesthetics of the hinge-pin design.
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Use tubing as a hinge pin for design and speed of installation
Tubing can be used as a hinge pin, and it offers several advantages. Firstly, tubing used as a hinge pin can be lightweight, which is an important design consideration. Secondly, it can provide rapid and easy installation, making it a convenient choice for quick assembly. Thirdly, tubing provides design flexibility in terms of colour and aesthetics. For example, a tube of a different colour can be set as a hinge pin, and then a wire of yet another colour can be slid through the tube to create a unique pattern. This decorative effect can enhance the visual appeal of the hinge.
When using tubing as a hinge pin, it is important to ensure a secure fit. One effective method is to bevel the ends of the hinge pin slightly and use a tube with a reasonable wall thickness. The tube should jut out slightly from the edge of the hinged part. By upsetting and thickening the tube, it can be flowed over the bevelled end of the hinge pin, securely fixing it in place. This technique, however, requires careful planning as the tube will become slightly shorter during the process.
Another option for installing a tubing hinge pin is to flare one side of the tube first and then insert it into the hinge. This method creates a tube rivet, providing a strong and rapid installation. Additionally, the openings of the tube can be bevelled slightly to enhance the purchase of the rivet, resulting in a good flush rivet. A round burr is an ideal tool for beveling as it automatically stays centred in the hole, ensuring a precise bevel.
It is worth noting that tubing hinge pins can also be utilised for functional purposes beyond aesthetics and rapid installation. For example, the hollow nature of the tubing allows for the threading of additional components through the hinge pin. This versatility enables the incorporation of additional design elements or structural reinforcements within the hinge assembly. Furthermore, tubing hinge pins can be strategically employed to reduce weight in specific applications, making them a valuable option in projects where weight optimisation is a critical factor.
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Frequently asked questions
A plastic hinge-pin can be designed with a solid pin or a coiled-spring pin. Coiled-spring pins are functional springs and are used in free-fit and friction-fit hinges. Free-fit hinges have little to no friction when the handle rotates, while friction-fit hinges require interference to prevent free rotation of components.
Coiled-spring pins match or exceed the performance of solid pins while lowering costs. They are well-suited for free-fit and friction-fit hinges and allow for better load distribution and closer-tolerance hinges.
Plastic is a reasonably weak material, so you may need to use oversized dimensions to achieve stiffness and strength. The shaft of the hinge-pin needs strength, especially at its attachment points, while the barrel will be stronger at the centre. It is also important to bevel the openings of the tube slightly to give the rivet a better purchase and produce a good flush rivet.
