Garage Door Components and Mechanisms

Garage doors are not merely doors, they are systems made up of mechanical and structural components that collectively lift and secure an exceptionally heavy panel or panels. Each component performs a critical job; the rollers, the tracks, hinges, springs, cables and motors work together to safely and effectively move the door up and down as desired.

Each component used in homes and commercial locations are all similar and based on the same ideas, but will vary in size and weight ratings.

Door Panels and Construction

The actual door of most garage doors consists of panels or sections. A typical overhead sectional door has horizontal panels (or slats) connected with hinges, so the door can bend as it travels on the track. Panels can be constructed from steel (often double-walled and insulated), wood (solid or composite), aluminum, fiberglass, or even full-view glass.

Some panels incorporate slats, as with wood and composite materials. Many panels are made with a foam core or other insulation layer to improve energy performance and stiffness. For instance, steel garage door panels often contain polyurethane or polystyrene insulation to limit heat transfer and noise. Each panel may also have struts or braces for reinforcement, usually metal, to prevent the panel from sagging under its own weight, especially for wider doors.

Some doors have small windows built into the panels to allow limited light while preventing significant visibility into the garage. Older tilt-up doors use a single, solid panel that swings outward using metal hinges at the top outside corners. Most modern doors consist of a number of connected sections, rather than just one panel.

Frame, Tracks, and Rollers

The garage door panels are supported by a steel frame and guided by a steel rail system. Each side of the door opening has a vertical track (rail) that arcs over into a horizontal track that is mounted along the ceiling. Small wheels called rollers with ball bearings are attached to the brackets on the edges of the garage door and roll inside the vertical and horizontal tracks that guide the garage door door up and down. The rollers can be made of nylon (quiet smooth operation) or steel (durable), and slides or rolls on the track as the pullies move the door or the spring system lifts the door.

If the track is bent or misaligned, the garage door will not operate properly and could get stuck or make scraping noises, requiring proper alignment of the track and lubricated rollers to move properly. Multi-panel doors have hinges that connect individual sections or panels. Each panel (other than the top and bottom panels) is equipped with hinges on both ends of the panels that allow the panels to fold (or bend).

The hinges are the point of attachment between each panel, and the panels utilize roller shafts that run through the hinge knuckles of the hinges. Therefore, as the garage door travels around the arc of the track, the panels bend at the hinges. The bottom brackets, or bottom corners of the panels, have brackets that help hold the rollers and cables..

Some heavy duty door systems even have horizontal strut brackets that are bolted across each panel to help reinforce strength for wind loads or stiffen the lateral movement of very wide doors. The track assembly is connected to the building structure using angle iron and anchors so that the door is adequately supported above the opening while it is opened.

Springs and Counterbalance System

Garage doors are very heavy, so springs assist in counterbalancing the weight. Garage doors typically use two different types of springs, torsion, and extension. A torsion spring is a long coil of steel wrapped around a steel shaft and is located above the door opening. The torsion spring is thoroughly wound when the door is closed or at rest, storing energy.

As the door opens, the torsion spring unwinds, which is what helps lift the door. Residential garage doors generally are configured with one or two torsion springs and commercial garage doors usually use several heavy-duty torsion springs that are rated for tens of thousands of use cycles. The ends of the coil wrap are anchored to stationary brackets attached to the wall, and the middle of the coil is attached to the torsion shaft, which allows for twisting as the door has a vertical motion.

There is also an extension spring, which is the older style, which mounts on the sides of the door and above the horizontal tracks. A pair of extension springs stretches as the door is lowered, and then contracts when the door is lifted. The extension spring travels with the use of a pulley, or pulley system that lifts with a cable attached to the springs.

Due to the high tension extension springs must undergo, they can be dangerous when they break, and thus they should always be safety-cabled so the fracture fragments from the broken spring do not pose a greater risk. Torsion springs are generally safer and have become more common in modern installations. Adjusting the spring tension is very simple, and is so critical to obtaining the desired performance of the door. When the spring tension is set properly during adjustment, the door should lift with very little applied force, and the door should also sit in a "no force" position if lifted to half the distance up into an open position.Spring systems also include a torsion shaft and end-bearing plates.

The torsion shaft (steel bar) runs across the top of the door with the springs mounted on it. The end bearing plates at each end of the shaft allow the torsion shaft to rotate when the springs unwind or wind up. On each end of the torsion shaft, there is a cable drum (also called a lift drum) fastened to the torsion shaft. As the spring unwinds, the shaft rotates causing the drums to wind up the lifting cables.

Cables, Drum, and Pulleys

Heavy steel lift cables attach the bottom corners of the door to the drums or pulleys at the top. On doors with torsion spring, there is a cable anchored to the bottom bracket on each side of the door that runs up around a drum on the torsion shaft. When the door is closed, the cables unwind from the drums, and when it is opened the cables wind up on the drums. This unwinding and winding action lifts the door with equal lift on both sides and is powered by the torsion spring.

In an extension-spring system, cables are attached to the bottom brackets and routed through the pulleys in the top corners of the door. The cable then connects to the extension spring, the extension springs pulls on the cables to lift the door. Whether in a torsion-system or extension-system, the important point is that the cables and drums convert the energy stored in the spring into lift on the door. Properly sized drums, which seemingly have a little less radius as the cable winds up, keep consistent tension and ensure the cable winds properly. If the cables stretch or fray or the drums wear, the door can become unbalanced.

Hinges, Brackets and Struts

There are various metal brackets and hinges which hold the door and its hardware to the door. Hinges between panels have been previously described, but there are also bottom fixtures, center brackets, and guide brackets. The bottom fixture or corner bracket is attached to the bottom panel and provides attachment for the roller and the end of the cable. There may be a center bearing plate and center bracket on the torsion shaft, depending on the design, which provide support from the middle.

Torsion springs are typically mounted to anchor brackets at each end of the garage door opening. There are often horizontal and vertical reinforcement struts across the panels; their importance increases with single-car or extra wide doors. These steel plates (or tubes) act to stiffen the panels and prevent sag or bowing, particularly important for high-wind areas or very wide doors. Without these struts, a large panel can flex to the point that it becomes misaligned and can create noise. All of the brackets and struts are held together with nuts and bolts. Loose hardware is a common mistake with doors.

Weather Seals, Locks, and Accessories

Garage doors come with rubber weatherseals to keep the weather out. A bottom seal (a vinyl "U" or bulb gasket) is installed along the bottom of the lowest panel compressing against the floor or threshold. The side seals consist of the rubber strip attached to the door frame on both sides and a header seal mounted along the top of the frame, pressing against the door.These seals protect against water, wind, insects, and debris while improving insulation uptime, all of which can crack or wear over time and need replacing. Security and manual operation require extra components.

Most garage doors designed for manual operation will have a lock, generally a slide bolt that either locks the door to the floor (for example, with a metal pin dropping into a notch in the floor track) or to the side jamb. Manual garage doors often have a handle on either an exterior or interior surface for lifting purposes and a latch mechanism inside to keep the door closed when left unattended. Automatic garage doors have an emergency release mechanism with a pull cord, typically finished with a cotton or vinyl handle on the top side, that hangs from the opener trolley nearby. One pull of this emergency release disconnects the door from the opener to permit the door to be operated by hand during a power outage. Some garage doors also have a manual trolley disconnect or keyed wall switch for a full lockout on the opener.

Manual Operation Options

Even when there is an installed electric opener, manual operation is possible on all doors. This is done with a lift handle or rope and, where applicable, a ratchet or spring-assisted balance to avoid slamming. An installed manual release on the opener (as mentioned above) allws the motor drive to disengage so the door can operate freely. The door should be easily raised or lowered by hand after disengaging. The springs should counterbalance gravity to avoid the door being too heavy because a great deal of the door weight will be offset by the springs. Many garage doors use nylon rollers and operate well with well-maintained springs so that doors operate nicely as a manual option.There are also doors that have a bottom "people door" (or pedestrian door), to facilitate access while the main door is closed; however, primarily commercial doors and side doors have this option over residential overhead doors.

Automatic Garage Door Openers

Essentially doors are automatic by using an electric garage door opener. An automatic opener is, in fact, a motorized unit that is installed to the ceiling (or on the wall next to the door in a jackshaft configuration). The opener contains an electric motor that turns a gear; the gear moves a chain, belt, or screw-threaded rod along a specified motion path. On the same path or track is a trolley (carriage) that connects, with an arm, to the top of the garage door. When the motor runs, it moves the trolley; this ultimately pushes or pulls the door closed or opened.

There are three common types of drive:

Chain Drive: This uses a roller chain (like a bicycle chain) that loops around the gears. The motor turns the gear, this pulls the chain and moves the trolley. Chain drives are very popular and durable in both residential and commercial units but will tend to be the noisier drive option of the three.

Belt Drive: Here a reinforced rubber belt takes the place of the chain in a chain drive. These devices are much quieter than chain drives and are very popular and often installed when the garage is connected to a living space. Belt drives operate similarly to chain drives with regard to layout. They use a toothed rubber belt instead of a roller chain around the motor gear.

Screw Drive: Here a long threaded steel rod (screw) runs along the length of the bolt. The trolley has a nut that now travels along the rod when the motor turns the screw.Screw drives utilize fewer moving parts and are much quieter than other drives; require less maintenance; but if it's very cold and you don't have lubrication, may not work as well.

Direct Drive: The motor drives the door directly, while travelling along a stationary rail (could be moving rail), some brands haven't even given the motor a rail, it travels along the ceiling. There is really no gear or belt to drive, the motor is the only moving part to the Direct drive opener, which makes the quietest.

For commercial overhead doors we have jackshaft openers, that mount on the wall beside the door, and turn the torsion shaft (generally, used in high ceilings or roll-up doors), we also have chain horse operators that use a gear motor that is heavy duty and chain to move very large doors. When it comes to motor horsepower, its driven by the door weight and how many times it gets opened and closed. A typical residential opener is going to be 1/2 to 3/4 hp, while the commercial operator can be 1 hp or more and is designed for opening and closing of many times in a row.

The operator housing actually contains the motor, gearbox, drive sprocket and circuit board. The circuit board is the brain of the operation: it receives inputs from the remote or wall switch, manages the limit and force settings, and takes care of safety inputs. Most operators will have- a light bulb (most LED nowadays) that lights up when the door goes up or down and many models have some sort battery backup for when the power goes out and the door must be opened.

Controls, Sensors, and Safety Systems

Automatic garage door systems typically use both wireless and wired controls to safely operate the garage door. A wall-mounted push-button panel is a common control (with an "open/close" button and a light switch) and handheld remote transmitters. The remote transmitters send coded radio signals (usually includes rolling-code technology for security) to a receiver in the opener to instruct and indicate to the opener to begin moving. There is also often a wireless keypad control that is mounted outside. In this case, the operator enters a PIN code and pushes enter to open the garage door - rather than using a remote.

It is common today to find openers that are equipped with Wi-Fi or smart-home modules that allow the garage door operator to operate the opener via smartphone applications or smart assistants for remote access/monitoring. The safety sensors are very important. All automatic openers have photoelectric "eye" sensors mounted on either side of the door at about a 4 - 6 inch height off the ground. These sensors beam an invisible infrared light across the doorway. If the beam is broken while the door is closing (e.g. person or object obstructs the path) the opener will respond immediately by stopping the door closing and will reverse the door, preventing possible injury and/or damage.

Some commercial systems will also use a pressure-sensitive safety edge (the rubber strip on the bottom of the door) to trigger a reversal when the safety edge comes into contact with an obstacle before or during contact with an obstruction.The opener's control board also senses the door's travel. If excessive resistance (beyond a certain amount of force) or obstruction is encountered during the door closing (as when an unsuspecting dog ambles through the opening), the door will reverse direction. Collectively, these features keep the door from crushing owners' vehicles, dogs, or children.

Other automatic operation components are the limits switches (which tell the motor when to stop opening or closing) and the emergency release previously discussed. The emergency release cable allows the plug-in trolley to disconnect from the opener. The trolley may be manually operated by someone who has broken or lost the remote and has little flat side. Be mindful to reattach the trolley the right way when finished operating manually. Some openers have a lock-out switch on the wall console, which disables the remotes (good for security, in case a remote is lost).

Residential vs Commercial Garage Door

Residential (home) and commercial garage doors share many of the same components but also have important differences in design and parts with the purpose of being able to do the task needed of a garage door, commercial or residential:

Size and materials - Commercial doors are larger and heavier. They commonly use thicker gauge steel or stronger aluminum (in industrial applications, there may be roll-up slats (steel curtains) rather than hinged panels). The high end commercial door may use a full-view aluminum frame with impact-resistant glass or polycarbonate. Residential doors typically use a lighter gauge panel of steelTorsion Springs - Most garage doors use torsion springs (rated in cycles; approximately 10,000 total cycles).

Commercial garage doors may go hundreds of cycles open and shut every day; thus, they have high cycle torsion springs that are rated 20,000, 50,000 or even more total cycles. Higher cycle torsion springs, which usually must be made of thicker steel, tend to exhibit breakage less frequently and require significantly less servicing than just a 10,000 rated cycle spring. Furthermore, extension type springs (if available in some exceptional cases), would not be offered or safe for larger commercial garage doors in similar installations.

Tracks and Rollers - For the regular consumer, the tracks for garage doors are fine for normal use; however, in commercial use, the track will be heavier duty due to the larger wind load on commercial doors. The rollers also have larger diameter bearing (3" or 4") than typical garage doors. Usually, heavy duty hinges or brackets that hold the door are reinforced too in the commercial setting. A few commercial tracks are flanged-mounted to add strength to the entire track system. Residential tracks and roller hardware will be just fine if they will have lighter garage doors that will not be excessively used; if used excessively, will wear over time.

Openers - Commercial doors typically use industrial grade operators i.e. either chain-bucket hoists or heavy duty chain drives and gear-reduction motors; if nothing else will typically be 1 HP, if not greater and will be intended for a high cycle life. Residential openers typically have a smaller motor (½ HP to ¾ HP) and are typically quieter (belt drives) and not intended for frequent use. Some commercial doors still have the manual back-up, hoist chain so if need be, someone can crank the door if needed.

Insulation and Seals - Commercial doors for warehouses or storage need to have better insulation and stronger seals for climate control; Commercial doors typically have better insulation boards in the curtain and have heavy-duty gasketing. Residential doors have their insulation but are more based on the aesthetics on the door (styles, adding windows), besides the thermal Performing insulation working to save energy for the Residence.

Security and Accessories - Some commercial doors will have special features like keycard readers, coded pushbuttons, magnetic locks for security. Other typical features are heavier duty, manual locks. For typical residential doors, the safety auto-reverse by the opener, relies on simplicity in the lock (or nothing if only operating by keypad/remotes).

There are many differences compared to commercial and residential garage doors; however, they all share the same core pieces, from the spring to cable, panels, track, and motor and safety sensors in the automating differences. By building on the basic, part knowledge differences to regard common maintenance distinctions and troubleshooting issues into understanding for the homeowner or end user is something.