A jackshaft, also called a countershaft, is a common mechanical design component used to transfer or synchronize rotational force in a machine. A jackshaft is often just a short stub with supporting bearings on the ends and two pulleys, gears, or cranks attached to it. In general, a jackshaft is any shaft that is used as an intermediary transmitting power from a driving shaft to a driven shaft.
The oldest uses of the term jackshaft appear to involve shafts that were intermediate between water wheels or stationary steam engines and the line shafts of 19th century mills. [1] [2] In these early sources from New England mills in 1872 and 1880, the term "jack shaft" always appears in quotes. Another 1872 author wrote "Gear wheels are used in England to transmit the power of the engine to what is usually called the jack shaft." [3] By 1892, the quotes were gone, but the use remained the same. [4]
The pulleys on the jackshafts of mills or power plants were frequently connected to the shaft with clutches. For example, in the 1890s, the generating room of the Virginia Hotel in Chicago had two Corliss engines and five dynamos, linked through a jackshaft. Clutches on the jackshaft pulleys allowed any or all of the dynamos to be driven by either or both of the engines. [5] With the advent of chain-drive vehicles, the term jackshaft was generally applied to the final intermediate shaft in the drive train, either a chain driven shaft driving pinions that directly engaged teeth on the inside of the rims of the drive wheels, [6] [7] or the output shaft of the transmission/differential that is linked by chain to the drive wheels. [8]
One of the first uses of the term jackshaft in the context of railroad equipment was in an 1890 patent application by Samuel Mower. In his electric-motor driven railroad truck, the motor was geared to a jackshaft mounted between the side frames. A sliding Dog clutch inside the jackshaft was used to select one of several gear ratios on the chain drive to the driven axle. [9] Later railroad jackshafts were generally connected to the driving wheels using side rods; see Jackshaft (locomotive) for details.
The term countershaft is somewhat older. In 1828, the term was used to refer to an intermediate horizontal shaft in a gristmill driven through gearing by the waterwheel and driving the millstones through bevel gears. [10] An 1841 textbook used the term to refer to a short shaft driven by a belt from the line shaft and driving the spindle of a lathe through additional belts. The countershaft and the lathe spindle each carried cones of different-diameter pulleys for speed control. [11] In 1872, this definition was given: "The term countershaft is applied to all shafts driven from the main line [shaft] when placed at or near the machines to be driven ..." [3]
Modern jackshafts and countershafts are often hidden inside large machinery as components of the larger overall device.
In farm equipment, a spinning output shaft on the rear of the vehicle is commonly referred to as the Power Take-Off or PTO, and the power-transfer shaft that is connected to it is commonly called a PTO shaft, but is also a jackshaft.
A clutch is a mechanical device that engages and disengages power transmission, especially from a drive shaft to a driven shaft. The clutch acts as a mechanical linkage between the engine and transmission; and briefly disconnects, or separates the engine from the Transmission system, and therefore the drive wheels, whenever the pedal is depressed, allowing the driver to smoothly change gears.
A tractor is an engineering vehicle specifically designed to deliver a high tractive effort at slow speeds, for the purposes of hauling a trailer or machinery such as that used in agriculture, mining or construction. Most commonly, the term is used to describe a farm vehicle that provides the power and traction to mechanize agricultural tasks, especially tillage, but nowadays a great variety of tasks. Agricultural implements may be towed behind or mounted on the tractor, and the tractor may also provide a source of power if the implement is mechanised.
A differential is a gear train with three shafts that has the property that the rotational speed of one shaft is the average of the speeds of the others, or a fixed multiple of that average.
A geared steam locomotive is a type of steam locomotive which uses gearing, usually reduction gearing, in the drivetrain, as opposed to the common directly driven design.
A lawn mower is a machine utilizing one or more revolving blades to cut a grass surface to an even height. The height of the cut grass may be fixed by the design of the mower, but generally is adjustable by the operator, typically by a single master lever, or by a lever or nut and bolt on each of the machine's wheels. The blades may be powered by manual force, with wheels mechanically connected to the cutting blades so that when the mower is pushed forward, the blades spin or the machine may have a battery-powered or plug-in electric motor. The most common self-contained power source for lawn mowers is a small internal combustion engine. Smaller mowers often lack any form of propulsion, requiring human power to move over a surface; "walk-behind" mowers are self-propelled, requiring a human only to walk behind and guide them. Larger lawn mowers are usually either self-propelled "walk-behind" types or more often, are "ride-on" mowers, equipped so the operator can ride on the mower and control it. A robotic lawn mower is designed to operate either entirely on its own or less commonly by an operator by remote control.
A power take-off or power takeoff (PTO) is any of several methods for taking power from a power source, such as a running engine, and transmitting it to an application such as an attached implement or separate machine.
A transmission is a machine in a power transmission system, which provides controlled application of power. Often the term 5-speed transmission refers simply to the gearbox, that uses gears and gear trains to provide speed and torque conversions from a rotating power source to another device.
A continuously variable transmission (CVT) is an automatic transmission that can change seamlessly through a continuous range of gear ratios. This contrasts with other transmissions that provide a limited number of gear ratios in fixed steps. The flexibility of a CVT with suitable control may allow the engine to operate at a constant RPM while the vehicle moves at varying speeds.
A manual transmission 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.
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.
A sprocket, sprocket-wheel or chainwheel is a profiled wheel with teeth, or cogs, that mesh with a chain, track or other perforated or indented material. The name 'sprocket' applies generally to any wheel upon which radial projections engage a chain passing over it. It is distinguished from a gear in that sprockets are never meshed together directly, and differs from a pulley in that sprockets have teeth and pulleys are smooth except for timing pulleys used with toothed belts.
A drive shaft, driveshaft, driving shaft, tailshaft, propeller shaft, or Cardan shaft is a vehicle component for transmitting mechanical power and torque and rotation, usually used to connect other components of a drivetrain that cannot be connected directly because of distance or the need to allow for relative movement between them.
A belt is a loop of flexible material used to link two or more rotating shafts mechanically, most often parallel. Belts may be used as a source of motion, to transmit power efficiently or to track relative movement. Belts are looped over pulleys and may have a twist between the pulleys, and the shafts need not be parallel.
A line shaft is a power-driven rotating shaft for power transmission that was used extensively from the Industrial Revolution until the early 20th century. Prior to the widespread use of electric motors small enough to be connected directly to each piece of machinery, line shafting was used to distribute power from a large central power source to machinery throughout a workshop or an industrial complex. The central power source could be a water wheel, turbine, windmill, animal power or a steam engine. Power was distributed from the shaft to the machinery by a system of belts, pulleys and gears known as millwork.
A horse engine is a machine for using draft horses to power other machinery. It is a type of animal engine that was very common before internal combustion engines and electrification. A common design for the horse engine was a large treadmill on which one or more horses walked. The surface of the treadmill was made of wooden slats linked like a chain. Rotary motion from the treadmill was first passed to a planetary gear system, and then to a shaft or pulley that could be coupled to another machine. Such powers were called tread powers, railway powers, or endless-chain powers. Another common design was the horse wheel or sweep power, in which one or several horses walked in a circle, turning a shaft at the center. Mills driven by horse powers were called horse mills. Horse engines were often portable so that they could be attached to whichever implement they were needed for at the time. Others were built into horse-engine houses.
A jackshaft is an intermediate shaft used to transfer power from a powered shaft such as the output shaft of an engine or motor to driven shafts such as the drive axles of a locomotive. As applied to railroad locomotives in the 19th and 20th centuries, jackshafts were typically in line with the drive axles of locomotives and connected to them by side rods. In general, each drive axle on a locomotive is free to move about one inch (2.5 cm) vertically relative to the frame, with the locomotive weight carried on springs. This means that if the engine, motor or transmission is rigidly attached to the locomotive frame, it cannot be rigidly connected to the axle. This problem can be solved by mounting the jackshaft on unsprung bearings and using side-rods or chain drives.
An idler-wheel is a wheel which serves only to transmit rotation from one shaft to another, in applications where it is undesirable to connect them directly. For example, connecting a motor to the platter of a phonograph, or the crankshaft-to-camshaft gear train of an automobile.
A steam motor is a form of steam engine used for light locomotives. They represented one of the final developments of the steam locomotive, in the final decades of the widespread use of steam power.
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.
A rope drive is a form of belt drive, used for mechanical power transmission.