Dog (engineering)

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In engineering, a dog is a tool or part of a tool, such as a pawl, that prevents or imparts movement through physical engagement. [1] 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.

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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.

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.

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.

Shutter dog

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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.

Ladder dog

Ladder dogs secure the sections of an extension ladder at a given height by engaging on its rungs, and are secured in place by spring-loaded pawls.

Door dog

Hatch dogs around a door on the R/V Knorr Door dogs.jpg
Hatch dogs around a door on the R/V Knorr

The watertight doors that allow passage through bulkheads between compartments inside a ship can be closed during emergencies to seal off one compartment from another, thus isolating flooding, smoke and heat from adjoining compartments. The objects that are wedged against the door to hold it closed are dogs. To dog the doors means to close the doors and secure them in the closed positions. Similarly, hatches are the horizontal openings between decks, and are secured with hatch dogs.

Firedog

A firedog, fire dog, or dog iron is a form of andiron used in a pair to secure wood for a fire or skewers for cooking over one.

Clutch dog

Clutch dogs are the individual lugs within a mechanism called the dog clutch , which comprises a pair of unconnected discs aligned axially, each with a radial arrangement of lugs which oppose one another and which interlock when the plates are in contact. Examples of dog clutches can be found in many vintage automobiles and are implemented in some modern automatic transmissions. The dog clutch contrasts with the friction clutch , the most basic form of which comprises a smooth disc and pressure plate: when pressed together they lock up simply through friction, which permits some degree of slip as the mating pressure is modulated and thus permits some difference in the rotational speeds of the discs. A dog clutch, however, is a binary system, thus requiring that the rotating speeds of the two discs be matched prior to mating to avoid damage by jerk within the system - this can be achieved automatically, such as by implementing a synchromesh mechanism, or manually, as in a crash gearbox.

Lathe dog

A lathe dog (or "lathe carrier") is a form of clutch dog used to secure a workpiece to a metal 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.

Drive dog or reel dog

In film projection, reel arms and film rewinds employ drive pins adjacent to the spindle shaft, which are used to drive the reel as the spindle rotates. These are referred to as drive dogs or reel dogs.

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<span class="mw-page-title-main">Clutch</span> Mechanical device that connects and disconnects two rotating shafts or other moving parts

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<span class="mw-page-title-main">Fishing reel</span> Hand-cranked reel used in angling to stow fishing line

A fishing reel is a hand-cranked reel used in angling to wind and stow fishing line, typically mounted onto a fishing rod, but may also be used to retrieve a tethered arrow when bowfishing.

<span class="mw-page-title-main">Lathe</span> Machine tool which rotates the work piece on its axis

A lathe is a machine tool 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.

<span class="mw-page-title-main">Automatic transmission</span> Type of motor vehicle transmission that automatically changes gear ratio as the vehicle moves

An automatic transmission is a multi-speed transmission used in motor vehicles that does not require any input from the driver to change forward gears under normal driving conditions.

<span class="mw-page-title-main">Manual transmission</span> Motor vehicle manual gearbox; stick shift

A manual transmission (MT), also known as manual gearbox, standard transmission, or stick shift, is a multi-speed motor vehicle transmission system, where gear changes require the driver to manually select the gears by operating a gear stick and clutch.

<span class="mw-page-title-main">Freewheel</span> Mechanism which disconnects a driveshaft from a faster-rotating driven shaft

In mechanical or automotive engineering, a freewheel or overrunning clutch is a device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft. An overdrive is sometimes mistakenly called a freewheel, but is otherwise unrelated.

<span class="mw-page-title-main">Limited-slip differential</span> Differential gearbox that limits the rotatational speed difference of output shafts

A limited-slip differential (LSD) is a type of differential that allows its two output shafts to rotate at different speeds but limits the maximum difference between the two shafts. Limited-slip differentials are often known by the generic trademark Positraction, a brand name owned by General Motors and originally used for its Chevrolet branded vehicles.

<span class="mw-page-title-main">Sprag clutch</span> One-way mechanical transmission device

A sprag clutch is a one-way freewheel clutch. It resembles a roller bearing but, instead of cylindrical rollers, non-revolving asymmetric figure-eight shaped sprags, or other elements allowing single direction rotation, are used. When the unit rotates in one direction the rollers slip or free-wheel, but when a torque is applied in the opposite direction, the sprags tilt slightly, producing a wedging action and binding because of friction.

<span class="mw-page-title-main">Lathe dog</span>

A lathe dog is a mechanical device typically made of cast iron, steel or aluminum that transmits rotary motion from a faceplate to a workpiece mounted between centers in a lathe. The tail of the dog is rotated by a slot in a driving faceplate, a stud mounted on a faceplate, or sometimes a side of a chuck jaw. The workpiece passes through an aperture in the dog into which the work is secured by one or more setscrews or a clamp arrangement. The maximum cross sectional dimension of the workpiece is limited by the dimensions of the dog aperture. Lathe dogs are provided in straight tail or bent tail form, and may be single tail or double tail. A lathe dog designed to hold square, rectangular or odd-shaped work and having a moveable portion secured typically by two cap screws is called a clamp dog. Bent tail dogs are able to engage directly with a driving faceplate slot or a chuck jaw but can crowd work off centre if clearance is not present between the dog tail and a closed end of the faceplate slot. Straight tail dogs do not present the issue of crowding work off centre but require at least one driving stud to be mounted on the faceplate. If the rotating mass of the dog setup is not balanced, eccentric motion of the work may occur. Counterbalancing or reduced spindle speed may be required. Care must be taken by the operator when using lathe dogs, as it is easy to get snagged on one. Use of headless setscrews, preferably of multiple-spline drive design, that do not protrude above the outer surface of the dog is recommended. A lathe dog may also be used with some indexing heads and other tools with similar faceplates that turn about a center.

The dog is a domesticated canid species, Canis familiaris.

<span class="mw-page-title-main">Rohloff Speedhub</span> Internal hub gear for bicycles

The Rohloff Speedhub is an epicyclic internal hub gear for bicycles, developed and patented by Rohloff AG. It has been manufactured and marketed by that company since 1998. The Speedhub 500/14 has 14 equally spaced, sequential, non-overlapping gear ratios operated by a single twistgrip. The overall gear range is 526%, meaning the highest gear is 5.26 times as high as the lowest gear. Individual gear shifts when shifting up give an increase of about 13.6%.

<span class="mw-page-title-main">Torque limiter</span>

A torque limiter is an automatic device that protects mechanical equipment, or its work, from damage by mechanical overload. A torque limiter may limit the torque by slipping, or uncouple the load entirely. The action of a torque limiter is especially useful to limit any damage due to crash stops and jams.

<span class="mw-page-title-main">Dog clutch</span>

A dog clutch is a type of clutch that couples two rotating shafts or other rotating components by engagement of interlocking teeth or dogs rather than by friction. 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. In engineering, a "dog" is a tool or device used to lock two components in relation to each other.

Machine – mechanical system that provides the useful application of power to achieve movement. A machine consists of a power source, or engine, and a mechanism or transmission for the controlled use of this power. The combination of force and movement, known as power, is an important characteristic of a machine.

<span class="mw-page-title-main">Electromagnetic clutch</span> Clutch that operates electrically but transmits torque mechanically

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.

<span class="mw-page-title-main">Motorcycle transmission</span> Transmission for motorcycle applications

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.

<span class="mw-page-title-main">Transmission brake</span>

A transmission brake or driveline parking brake is an inboard vehicle brake that is applied to the drivetrain rather than to the wheels.

<span class="mw-page-title-main">Layshaft</span> Mechanism in car gearboxes

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.

<span class="mw-page-title-main">Pawl</span> Mechanical device to restrict movement

A pawl is a movable lever that engages a fixed component to either prevent movement in one direction or restrain it altogether. As such, it is a type of latch and can also be considered a type of dog. It typically consists of a spring-loaded lever that engages a mating component at a steep enough angle to restrain it. Pawls are often tapered, being widened at their pivot for anchoring and narrow at their tip.

References

  1. "Definition of Dog -> In engineering a dog is 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". engineeringslab.com. Retrieved 2023-06-03.