This article takes an in depth look at concealed hinges.
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A concealed hinge, also known as a hidden or European hinge, is a type of hinge that has parts invisible to the onlooker when the door is closed. They are commonly used in cabinet doors to add an aesthetically pleasing and continuous appearance. Most modern concealed hinges are engineered to be installed on different door types and have a variety of features such as soft-close, adjustable arm, and easy dismount.
A concealed hinge is also called a cup hinge because of the cup-shaped piece that goes into the backside of the door. A recess is bored on the door to allow a flushed mounting. This recess also accommodates the arm of the hinge when the door is closed.
Unlike the usual barrel and leaf types, a concealed hinge is not composed of a separate barrel and pin. Instead, the pin is already fixed on the arm of the hinge. A concealed hinge is made up of three main parts: the hinge cup, the hinge arm, and the mounting plate.
Hinge Cup: The hinge cup is the part mounted on the door of the cabinet. The typical bore diameters for receiving the cup are 26, 35, and 40 mm. The depth of the bore varies depending on the construction of the hinge arm. The hinge cup has two flanges for screwing the metal at the backside of the door.
Hinge Arm: The hinge arm usually refers to the main hinge piece. This is the part where most of the design features are applied. The hinge arm connects the hinge cup installed at the backside of the door to the mounting plate installed at the frame of the cabinet. It has different forms depending on the type of cabinet door and the required travel or end play.
The hinge cup and hinge arm form the main hinge and are typically assembled together. Thus, a full concealed hinge set is typically composed of only two separated components: the main hinge and the mounting plate. One-piece sets are also available for compact applications.
Mounting Plate: The mounting is installed at the edge, side, or frame of the furniture. It has either two or four mounting holes depending on the weight or load imposed by the door. It has notches, clips, or holes for receiving the hinge arm.
Overlay and reveal are the two most commonly used terms in specifying the cabinet door design and concealed hinge specifications. These two dimensions affect the door position and the overall appearance of the cabinet doors.
The overlay is the term used to denote how much of the edge of the cabinet or cabinet frame is covered by the door. Opposite the overlay is the reveal which specifies the portion of the edge or frame of the cabinet that is not covered by the door.
The different amounts of overlay and reveal lead to the main classifications of concealed hinges.
Bi-Fold Concealed Hinge: This type of hinge is used in double doors of L-shaped corner cabinets. Ordinary overlay or inset concealed hinges are used to attach the door assembly to the cabinet frame while bi-fold concealed hinges are used to attach the two doors together. The result is a folding door with one side hinged on the cabinet.
Blind Corner Concealed Hinge: These hinges are used in inside-corner cabinets with a side panel inline and flushed with the door. Most blind corner hinge arm designs allow a full 90° opening of the cabinet door.
Corner Concealed Hinge: Also known as an angled concealed hinge, corner concealed hinges are used in doors hinged at the outside corner of the furniture. Most furniture outside corners are angled at 90°, but 30° and 45° angles also exist. For these types of furniture, a corner concealed hinge with the corresponding angle is available.
Face Frame-Type Concealed Hinge: A face frame cabinet has a small amount of fascia installed on the side panels of the cabinet. The mounting plate design of face frame-type concealed hinges is different for full overlay and inset concealed hinge types. The mounting plate of a full overlay type has screws oriented perpendicularly to the plate. The screws on the inset types are aligned at an angle and fixed at the backside of the frame.
Special concealed hinge designs are also available for less common cabinet types. Most of the other cabinet types are located at the inside and outside corners of the furniture. Examples of concealed hinges used in these areas are:
Full Overlay Concealed Hinge: This type of concealed hinge is used in cabinets where the door is positioned at the front of the cabinet box or frame. When closed, the periphery of the door‘s backside mates against the edge of the cabinet panels.
A full overlay does not necessarily mean that the door completely covers the entire cabinet box. Some designs allow some amount of reveal. The datasheet of most commercially available concealed hinges gives mounting plate dimensions, so the desired amount of overlay and reveal can be achieved.
Half Overlay Concealed Hinge: Half overlay concealed hinges are used in cabinets with two or more doors that are hinged on the same panel. This hinge design allows the two doors to share the allowable overlay from the thickness of the cabinet panel.
To achieve a half overlay installation, half overlay hinges use a cranked hinge arm and a raised mounting plate. These two features reduce the overlay taken by a single door.
Inset Concealed Hinge: Doors that use inset concealed hinges fit inside the cabinet panel or frame. Thus, the installation has no overlay. This design has the outer face of the door flushed on the outer surface of the frame or edge of the cabinet box.
The hinge arm of an inset concealed hinge is highly cranked. Also, the mounting plate is raised to fully eliminate the overlay.
Aside from the desired overlay, cabinets can also have different frame constructions. The corresponding hinge type must be employed for proper attachment.
In addition to type, concealed hinges are selected according to different specifications and features.
Hinge Cup Size or Bore Diameter: As mentioned in the previous chapter, the hinge cup can have different sizes. Each size represents a type of application.
Attachment Type: The attachment type refers to how the hinge arm attaches to the mounting plate. There are two main types: clip-on or slide-on.
Clip-On: The design of a concealed hinge with a clip-on attachment makes for effortless door mounting and dismounting. This is useful on doors with multiple hinges as it allows door installation in one movement. There is no need to use screws and screwdrivers.
A typical clip-on hinge has a clip tab located at the rear end of the hinge arm right next to the depth adjustment screw. Mating the hinge arm on the mounting plate latches both parts in place using the clip-on assembly. The attachment can be released by pressing or pulling the clip tab.
Slide-On: This is the traditional attachment type of concealed hinges. Slide-on hinges are much simpler in construction: a slot or notch on the hinge arm and a hole on the mounting plate. The two parts of the hinge are set by a fixing screw.
The slot on the slide-on design is not just for fixing the hinge arm on the mounting plate but also for adjusting the depth of the hinge.
Number of Concealed Hinges Per Door: Manufacturers usually provide a chart for determining the recommended number of hinges to use. The number of hinges needed depends on the height, weight, and in some cases, the width of the door.
A 40 inch (101.6 cm) tall door typically requires two hinges. Adding another 20 inches (50.8 cm) to its height adds another hinge. Thus,
This is all true regardless of the weight of the door.
In terms of the weight or load applied on the door, a 15 pound (6.8 kg) door usually requires two hinges. Adding another 15 pounds (6.78 kg) necessitates another hinge, and so on. This is applied regardless of the door height. Note that this 15-pound value is highly likely to vary depending on the design, material, and thickness of the hinge. The specified weight varies more than the height when comparing product datasheets.
When considering both height and weight, if the two yield different requirements for the number of hinges, the larger number is always followed.
Closing Action: The closing action refers to the manner in which the door closes without the aid of any external force. There are three popular options: self-close, soft close, and free swing.
Self-Close: As the name suggests, a self-closing concealed hinge automatically closes the door and keeps it from creeping open. This is done mechanically through the design of the hinge arm. The hinge arm has a small spring mechanism that returns the hinge to its resting or closed position. The spring is carefully designed so that when the door is opened to a certain degree, there is not enough torque or force to pull the door.
The closing action only occurs at the "tipping point" of the hinge arm. The tipping point is at the 10 to 20-degree position of a partially opened door.
Soft-Close: This type of concealed hinge has an integrated hydraulic damping mechanism. When the door is left partially opened and over the tipping point of the closing mechanism, the damper activates to gradually and silently closes the door. This prevents unwanted slamming that can damage the furniture. The damper offers significant resistance that even makes it hard to force close the door. The soft closing feature is considered a self-closing design but with additional technology.
Some soft-close mechanisms allow adjustments to the damping or closing resistance. The damping system can be adjusted to have high resistance and long closing action or low resistance and faster closing action.
Free Swing: Free swing concealed hinges are the simplest among the three types. They do not have a self-closing mechanism. Thus, the door can freely swing on its entire range of opening without encountering resistance or a tipping point. Doors fitted with free swing hinges rely on magnetic and mechanical latches for keeping the door closed.
Degree of Opening: This specification is defined as the angle made by the door and the frame of the cabinet at the door‘s fully open position. The degree of opening is sometimes called the range of opening or door swing.
The minimum degree of opening of concealed hinges is about 100°. Concealed hinges with opening angles below 100° are considered low angle types. Depending on the hinge design, the most common hinges have an opening of 100° to 120°. Going beyond 120° results in more expensive hinges with complex hinge arm mechanisms. The maximum degree of opening is 270°, which allows the door to swing back against the cabinet.
Lateral Adjustment: When facing the cabinet door, adjusting this screw moves the position of the hinge arm either left or right. It affects the reveal, or the portion of the cabinet not covered by the cabinet door for a frameless cabinet. Also, if the cabinet type is a two-door cabinet, the lateral adjustment changes the space or gap between the two doors. The lateral adjustment typically allows 5 mm of movement.
Correcting the lateral adjustment is one of the hardest tasks when installing a concealed hinge. Most of the time, this is when the imperfections of the furniture structure are revealed. Luckily, this is done mechanically by turning the screw. Thus, adjustment can be done incrementally. The lateral adjustment of one concealed hinge is accomplished in tandem with the other hinge installed on the door. The coordinated adjustment of the concealed hinge pair slightly tilts the door. Too much adjustment can lead to a door appearing to sag on one side.
Depth Adjustment: Turning a depth adjustment screw allows an in-and-out or front-to-back movement of the door from the cabinet. This feature is used to control the gap between the frame and the backside of the door when the cabinet is closed.
The typical design of the depth adjustment is an elongated slot or notch punched near the rear end of the hinge arm or piece. This slot mates to a hole located on the mounting plate. Loosening the fixing screw on the mounting plate allows the hinge arm to slide in and out. This configuration allows 3 to 5 mm of movement. Other high-tech designs, like Blum‘s proprietary Spiral Tech, do not use a fixing screw. Instead, the depth is changed by turning the adjustment screw with a preset number of revolutions. Spiral Tech allows 5 mm of movement by turning the depth adjustment screw one and three-quarter revolutions.
Height Adjustment: The height adjustment feature of a concealed hinge allows for changing the position of the door in the vertical direction. This is used to ensure the top and bottom edges of the door match properly on the corresponding edges of the cabinet.
The height adjustment is integrated into the mounting plate. Some designs feature a mounting plate with elongated slots. These slots match up with holes drilled on the edge of the cabinet. Loosening the fixing screws allows a small amount of movement by sliding the mounting plate up or down. The height adjustment is typically small and can range from 2 to 3 mm.
Types of Mounting Fasteners: There are two basic types of mounting screws for both the hinge cup and mounting plate:
Hinge Material: Concealed hinges are typically made of stainless steel. Stainless steel has excellent mechanical properties, a variety of surface finishes, and inherent corrosion resistance. Other materials used for fabricating concealed hinges are nickel-plated steel, galvanized steel, and brass.
Other Dimensions and Measurements: Below is some additional information for specifying concealed hinge requirements. It is recommended to look into charts and tables that specify these values for precise and accurate mounting.
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