Dog (engineering)

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In engineering, a dog is a tool or part of a tool that prevents movement or imparts movement by offering physical obstruction or engagement of some kind. It may hold another object in place by blocking it, clamping it, or otherwise obstructing its movement. Or it may couple various parts together so that they move in unison – the primary example of this being a flexible drive to mate two shafts in order to transmit torque. Some devices use dog clutches to lock together two spinning components. In a manual transmission, the dog clutches, or "dogs" lock the selected gear to the shaft it rotates on. Unless the dog is engaged, the gear will simply freewheel on the shaft.

Tool physical item that can be used to achieve a goal

A tool is an object used to extend the ability of an individual to modify features of the surrounding environment. Although many animals use simple tools, only human beings, whose use of stone tools dates back hundreds of millennia, use tools to make other tools. The set of tools needed to perform different tasks that are part of the same activity is called gear or equipment.

Torque tendency of a force to rotate an object

Torque, moment, or moment of force is the rotational equivalent of linear force. The concept originated with the studies of Archimedes on the usage of levers. Just as a linear force is a push or a pull, a torque can be thought of as a twist to an object. The symbol for torque is typically , the lowercase Greek letter tau. When being referred to as moment of force, it is commonly denoted by M.

Dog clutch coupling

A dog clutch is a type of clutch that couples two rotating shafts or other rotating components not by friction but by interference. The two parts of the clutch are designed such that one will push the other, causing both to rotate at the same speed and will never slip.


This word usage is a metaphor derived from the idea of a dog (animal) biting and holding on, the "dog" name derived from the basic idea of how a dog jaw locks on, by the movement of the jaw, or by the presence of many teeth. In engineering the "dog" device has some special engineering work when making it – it is not a simple part to make as it is not a simple bar or pipe, and the metal used in its construction is likely to be special rather than regular steel.

Metaphor Figure of speech

A metaphor is a figure of speech that, for rhetorical effect, directly refers to one thing by mentioning another. It may provide clarity or identify hidden similarities between two ideas. Antithesis, hyperbole, metonymy and simile are all types of metaphor. One of the most commonly cited examples of a metaphor in English literature is the "All the world's a stage" monologue from As You Like It:

There is potential for confusion as "dog tensioners" are levers that are named due to the shape of the lever appearing as a dog leg, as the lever is in a pantograph arrangement, or "dog trailers", which are named due to the use of multiple trailers for transporting animal cages.

Pantograph drawing tool

A pantograph is a mechanical linkage connected in a manner based on parallelograms so that the movement of one pen, in tracing an image, produces identical movements in a second pen. If a line drawing is traced by the first point, an identical, enlarged, or miniaturized copy will be drawn by a pen fixed to the other. Using the same principle, different kinds of pantographs are used for other forms of duplication in areas such as sculpture, minting, engraving, and milling.

Subtypes and examples of applications

Chainsaw dog

Although not seen on all chainsaws, when present chainsaw dogs are mounted where the bar meets the power head. Chainsaw dogs provide stability and serve as a sort of fulcrum for swinging the bar through the item being cut.


A chainsaw is a portable, mechanical saw which cuts with a set of teeth attached to a rotating chain that runs along a guide bar. It is used in activities such as tree felling, limbing, bucking, pruning, cutting firebreaks in wildland fire suppression and harvesting of firewood. Chainsaws with specially designed bar and chain combinations have been developed as tools for use in chainsaw art and chainsaw mills. Specialized chainsaws are used for cutting concrete. Chainsaws are sometimes used for cutting ice, for example for ice sculpture and in Finland for winter swimming. Someone who uses a saw is a sawyer.

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Shutter dog

Shutter dog

Functional exterior window shutters (which can be swung shut whenever storms approach in order to protect the window glass from impact by wind-blown debris) are held open during pleasant weather by wrought-iron or cast-iron dogs, which are called shutter dogs.

Bench dog

A bench dog is an accessory used on a woodworking workbench to allow clamping of wooden items whilst being worked.

Bench dog

A bench dog is an accessory used on a woodworking workbench to allow clamping of wooden items while being worked or planed. Dog in general is something which holds. At its most basic a bench dog is simply a peg which is installed in a corresponding dog hole in the top of a bench. The holes are arranged in a line perpendicular to the vise, perhaps three or four inches apart but certainly no further apart than the fully open distance between the vise's jaws.

Workbench (woodworking)

A workbench is a table used by woodworkers to hold workpieces while they are worked by other tools. There are many styles of woodworking benches, each reflecting the type of work to be done or the craftsman's way of working. Most benches have two features in common: they are heavy and rigid enough to keep still while the wood is being worked, and there is some method for holding the work in place at a comfortable position and height so that the worker is free to use both hands on the tools. The main thing that distinguishes benches is the way in which the work is held in place. Most benches have more than one way to do this, depending on the operation being performed.

Ladder dog

Ladder dogs are the parts of a ladder that hold the ladder at a certain height, and articulate against pawls to allow adjustment.

Hatch dog

A hatch on USS Blue Ridge with the hatch dogs clearly visible. US Navy 080815-N-8546L-014 Sailors assigned to the engineering repair division aboard the amphibious command ship USS Blue Ridge (LCC 19) raise an external hatch to perform maintenance on the watertight gasket and moving parts.jpg
A hatch on USS Blue Ridge with the hatch dogs clearly visible.

The doors that allow passage through bulkheads between compartments inside a ship can be closed during emergencies to seal off one compartment from another, thus sequestering water leaks, fires, or waves of air pressure and preventing them from compromising the rest of the ship's interior. The objects that are wedged against the door to hold it closed against the water or air pressure are an example of dogs. To dog the hatches means to close the hatches and dog them down (fasten them closed).

Firedog (alias dog iron, andiron)

Andirons, which hold up the firewood in a fireplace, are sometimes called dogs, firedogs, or dog irons.

Clutch dog

The clutch that mates the engine to the transmission in a modern manual-shift automobile is a friction clutch whose disc and pressure plate are smooth; they lock up simply through friction. However, some kinds of clutches (including those inside an automatic transmission) may lock up via the engagement of dogs, rather than only through friction. These clutches are called dog clutches and the dogs used within them are called clutch dogs.

Lathe dog

The lathe dog (or lathe carrier) is essentially analogous to a clutch dog. It is used to provide positive drive to a workpiece turning between centers on a lathe. Without the dog, the cutting tool would tend to "catch", e.g., stop the workpiece from turning while the headstock center continued to rotate, possibly causing damage to the workpiece, or the lathe.

Feed dog

The feed dogs of a sewing machine feed the fabric in a linear stepping motion past the needle.

Log dog or timber dog

In carpentry log dogs were used to repair timber frame joints. In hewing (shaping with an axe) timbers or sawing with some types of water powered sawmills log dogs are used to hold the timber in place.


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Clutch machine element for rigid, elastic, movable or releasable connection of two shafts

A clutch is a mechanical device which engages and disengages power transmission especially from driving shaft to driven shaft.

Lathe machine tool which rotates the workpiece on its axis

A lathe is a machine that rotates a workpiece about an axis of rotation to perform various operations such as cutting, sanding, knurling, drilling, deformation, facing, and turning, with tools that are applied to the workpiece to create an object with symmetry about that axis.

Manual transmission type of transmission used in motor vehicle applications

A manual transmission, also known as a manual gearbox, a standard transmission or colloquially in some countries as a stick shift, is a type of transmission used in motor vehicle applications. It uses a driver-operated clutch, usually engaged and disengaged by a foot pedal or hand lever, for regulating torque transfer from the engine to the transmission; and a gear selector that can be operated by hand or foot.

Collet mechanical device to hold a separate piece

A collet is a subtype of chuck that forms a collar around an object to be held and exerts a strong clamping force on the object when it is tightened, usually by means of a tapered outer collar. It may be used to hold a workpiece or a tool.

Chuck (engineering) tool

A chuck is a specialized type of clamp used to hold an object with radial symmetry, especially a cylinder. In drills and mills it holds the rotating tool whereas in lathes it holds the rotating workpiece. On a lathe the chuck is mounted on the spindle which rotates within the headstock. For some purposes an additional chuck may be mounted on the non-rotating tailstock.

Punch press machine tool for punching

A punch press is a type of machine press used to cut holes in material. It can be small and manually operated and hold one simple die set, or be very large, CNC operated, with a multi-station turret and hold a much larger and complex die set.

Preselector gearbox

A preselector or self-changing gearbox is a type of manual gearbox used on a variety of vehicles, most commonly in the 1930s. The defining characteristic of a preselector gearbox is that the manual shift lever is used to "pre-select" the next gear to be used, then a separate control is used to engage this in one single operation, without needing to work a manual clutch.

Lathe center

A lathe center, often shortened to center, is a tool that has been ground to a point to accurately position a workpiece on an axis. They usually have an included angle of 60°, but in heavy machining situations an angle of 75° is used.

Lathe faceplate

A lathe faceplate is a basic workholding accessory for a wood or metal turning lathe. It is a circular metal plate which fixes to the end of the lathe spindle. The workpiece is then clamped to the faceplate, typically using t-nuts in slots in the faceplate, or less commonly threaded holes in the faceplate itself.

Centrifugal clutch clutch type using centrifugal force to connect concentric shafts

A centrifugal clutch is a clutch that uses centrifugal force to connect two concentric shafts, with the driving shaft nested inside the driven shaft. It engages more at higher speeds.

This glossary of woodworking lists a number of specialized terms and concepts used in woodworking, carpentry, and related disciplines.

Electromagnetic clutches operate electrically but transmit torque mechanically. This is why they used to be referred to as electro-mechanical clutches. Over the years, EM became known as electromagnetic versus electro-mechanical, referring more about their actuation method versus physical operation. Since the clutches started becoming popular over 60 years ago, the variety of applications and clutch designs has increased dramatically, but the basic operation remains the same today.

A power shuttle is an additional unit used in transmissions and is generally used in agricultural tractors. While the vehicle is moving forwards, the driver can pull a lever that makes it stop and go backwards at the same speed. Power Shuttles are also known under various trade names including Power Reverser

Shaving horse

A shaving horse is a combination of vice and workbench, used for green woodworking. Typical usage of the shaving horse is to create a round profile along a square piece, such as for a chair leg or to prepare a workpiece for the pole lathe. They are used in crafts such as coopering and bowyery.

Metal spinning

Metal spinning, also known as spin forming or spinning or metal turning most commonly, is a metalworking process by which a disc or tube of metal is rotated at high speed and formed into an axially symmetric part. Spinning can be performed by hand or by a CNC lathe.

Motorcycle transmission

A motorcycle transmission is a transmission created specifically for motorcycle applications. They may also be found in use on other light vehicles such as motor tricycles and quadbikes, go-karts offroad buggies, auto rickshaws, mowers and other utility vehicles, microcars, and even some superlight racing cars.

Layshaft An intermediate shaft within a gearbox that carries gears, but does not transfer power either in or out of the gearbox.

A layshaft is an intermediate shaft within a gearbox that carries gears, but does not transfer the primary drive of the gearbox either in or out of the gearbox. Layshafts are best known through their use in car gearboxes, where they were a ubiquitous part of the rear-wheel drive layout. With the shift to front-wheel drive, the use of layshafts is now rarer.