Crank (mechanism)

• 1. Mechanical Principles And Function

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  A crank is an arm attached at a right angle to a rotating shaft. This simple geometry allows circular motion to be imparted to or received from the shaft. When combined with a connecting rod, the mechanism converts circular motion into reciprocating motion. The reverse process also occurs as the device transforms back-and-forth movement into rotation. The arm itself may be a bent portion of the shaft or a separate disk attached to it. A pivot connects the end of the crank to a rod called a connecting rod. This connection point allows the transfer of force between the two components. Engineers use this arrangement in almost all reciprocating engines today. The pistons move linearly while the crankshaft turns continuously.

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• 2. Ancient Origins In Asia And Europe

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  Evidence of the earliest true crank handle appeared in Han era glazed-earthenware tomb models. These agricultural winnowing fans date no later than 200 AD. One specific model dates back to the Western Han dynasty which spanned from 202 BC to 9 AD. Chinese artisans used crank-and-connecting rods in ancient blasting apparatus and textile machinery by that time. The hand-crank of the rotary quern was different from a standard crank. It functioned as a combination of a hand-crank and a push-and-pull connecting rod joined by a hinge. Ancient Egyptians had manual drills resembling a crank during the Old Kingdom period between 2686 BCE and 2181 BCE. However their drill did not operate as a true crank mechanism. Later evidence for the crank combined with a connecting rod appears in the Hierapolis sawmill in Roman Asia. This machine operated during the 3rd century AD. Two stone sawmills at Gerasa and Ephesus also utilized these mechanisms in the 6th century AD. A Roman iron crank excavated in Augusta Raurica, Switzerland dates to the 2nd century AD. That long piece fitted a bronze handle at one end.

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• 3. Medieval Innovations And Renaissance Spread

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  A rotary grindstone operated by a crank handle appeared in the Carolingian manuscript Utrecht Psalter around 830 AD. The pen drawing goes back to a late antique original. A musical tract attributed to Abbot Odo of Cluny who died in 942 describes a fretted stringed instrument. This device used a resined wheel turned with a crank. Guido da Vigevano lived from 1280 to 1349 and planned illustrations for paddle boats propelled by manually turned compound cranks. His war carriages featured gear wheels alongside these cranks. The Luttrell Psalter dating to around 1340 describes a grindstone rotated by two cranks on its axle. The geared hand-mill appeared later in the 15th century. The crank became common in Europe by the early 15th century. German military engineer Konrad Kyeser depicted devices including cranked windlasses for spanning siege crossbows. He also designed cranked chain buckets for water-lifting operations. Kyeser equipped Archimedes screws for water-raising with a crank handle. This innovation replaced the ancient practice of working the pipe by treading. The earliest evidence for fitting a well-hoist with cranks appears in a miniature from about 1425.

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• 4. Industrial Applications And Engine Design

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  Almost all reciprocating engines use cranks with connecting rods to transform piston motion into rotary motion. These components are incorporated directly into a crankshaft. Steam locomotives utilize a specific type called a crank axle which serves as both shaft and axle. Internal combustion engines of the early 20th century were usually started with hand cranks known as starting handles in the UK. Electric starters eventually came into general use replacing manual methods. The last car model incorporating a crank was the Citroën 2CV produced between 1948 and 1990. A 1918 Reo owner's manual details how to hand crank an automobile engine. Operators had to ensure the gear shifting lever sat in neutral position first. They then unlatched the clutch pedal and engaged it fully. The brake pedal needed pushing forward as far as possible to set brakes on the rear wheel. Spark control levers required adjustment before turning the ignition switch. Fuel supply checks involved pressing down on a small pin projecting from the front of the bowl. If fuel failed to flood the carburetor the motor could not be expected to start. Operators grasped the handle of the starting crank to engage the ratchet with the crank shaft pin.

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• 5. Human Powered Mechanisms And Tools

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  The term often refers to a human-powered crank used to manually turn an axle. A person's arm or leg serves as the connecting rod applying reciprocating force to the crank. There is usually a bar perpendicular to the other end of the arm. This bar often features a freely rotatable handle or pedal attached. Examples include spinning wheels, mechanical pencil sharpeners, and fishing reels. The carpenter's brace functions as a compound crank mechanism. Hand winches rely on this principle for operation. Foot-powered cranks drive bicycle pedals through a specific crankset assembly. Treadle sewing machines utilize foot power converted by these mechanisms. Starting handles for older cars allowed drivers to rotate engines manually. Manually operated car windows also employed simple crank systems. Cranked rack-and-pinion devices called cranequins appeared in the 15th century. These fitted crossbow stocks to exert more force while spanning the missile weapon. Textile industry workers introduced cranked reels for winding skeins of yarn around that time. Around 1480 early medieval rotary grindstones improved with treadle and crank mechanisms. Cranks mounted on push-carts first appear in a German engraving from 1589.

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