the groove in a shaft for a key is called a
Key ( engineering ) - wikipedia Key ( engineering ) Jump to : navigation , search In mechanical engineering , a key is a machine element used to connect a rotating machine element to a shaft . The key prevents relative rotation between the two parts and may enable torque transmission . For a key to function , the shaft and rotating machine element must have a keyway and a keyseat , which is a slot and pocket in which the key fits . The whole system is called a keyed joint . A keyed joint may allow relative axial movement between the parts . Commonly keyed components include gears , pulleys , couplings , and washers . Contents ( hide ) 1 Types 1.1 Sunk key 1.1. 1 Parallel keys 1.1. 2 Woodruff keys 1.1. 3 Tapered keys 1.1. 4 Others 1.2 Saddle keys 1.3 Tangent Keys 1.4 Motoreta keys 1.5 Spline key 2 Keyseating 2.1 Broaching 2.2 Keyseater 2.3 Wire - cut EDM 2.4 Shaping or Slotting 2.5 Milling 2.6 Chiseling 3 Keyed joints 4 See also 5 References 5.1 Bibliography 6 External links Types ( edit ) There are five main types of keys : sunk , saddle , tangent , round , and spline . Sunk key ( edit ) Types of sunk keys : rectangular , square , parallel sunk , gib - head , feather , and Woodruff . Parallel keys ( edit ) Parallel keys are the most widely used . They have a square or rectangular cross-section . Square keys are used for smaller shafts and rectangular faced keys are used for shaft diameters over 6.5 in ( 170 mm ) or when the wall thickness of the mating hub is an issue . Set screws often accompany parallel keys to lock the mating parts into place . The keyway is a longitudinal slot in both the shaft and mating part . The keyseat in a shaft for a parallel key A sprocket with an internal parallel keyway Cross-section of a parallel keyed joint ( width ) W = d / 4 ( height ) H = ( 2 / 3 ) d ... ( d = diameter of shaft ) Woodruff keys ( edit ) Woodruff keys are semicircular , fitting partly into a circular segment keyway with the remainder fitting into a longitudinal slot keyway in the mating part . The circular segment can be cut directly by plunge cutting with a circular Woodruff cutter without any reliefs . The main advantage of the Woodruff key is the elimination of milling near shaft shoulders , where stress concentrations , and concentricity would be affected . The latter is particularly important for high speed operation . The more exact fit of the key and keyway also reduces play , and stress concentrations in , and improves the reliability of the key . An additional advantage is a stuck key can be removed from a shaft with a hammer blow , the circular profile will push the key out of the slot , as opposed to a standard key which will need to be pushed axially , or pulled out of its slot . Common applications include machine tools , automotive applications , snowblowers and marine propellers . This type of key was developed by W.N. Woodruff of Connecticut . In 1888 , he was awarded the John Scott Medal by the Franklin Institute for his invention . A Woodruff key installed A Woodruff key and keyway Gear G is positively located on shaft S by Woodruff key N Tapered keys ( edit ) The tapered key is tapered only on the side that engages the hub . The keyway in the hub has a taper that matches that of the tapered key . Some taper keys have a gib , or tab , for easier removal during disassembly . The purpose of the taper is to secure the key itself , as well as , to firmly engage the shaft to the hub without the need for a set screw . The problem with taper keys is that they can cause the center of the shaft rotation to be slightly off of the mating part . It is different from a tapered shaft lock in that tapered keys have a matching taper on the keyway , while tapered shaft locks do not . Others ( edit ) A Scotch key or Dutch key features a circular keyway hole ( instead of rectangular ) , produced by drilling axially into the assembled hub and shaft , with a metal dowel pin serving as the key . If the hole and key are tapered , the key is referred to as a Dutch pin , which is driven in and optionally finished by cutting or grinding flush with the end of the shaft . If a straight Dutch keyway hole is optionally tapped with a thread , then an ordinary screw serves as the threaded Dutch key . Spring pins are an alternative Dutch key component , instead of solid dowel pins . A spring pin is self - fastening and does not work loose under vibration . Hollow spring pins provide a weaker shear strength than a solid dowel pin , and the strength may be varied by varying the wall thickness . This limited shear strength specification is designed to sustain normal operation , but then give way in the event of excessive shaft torque , thus protecting the rest of the machine from damage . Introducing an additional bushing component between hub and shaft improves the performance and convenience of keyed joints . Taper - Lock bushings are keyed hub fittings which provide three threaded Dutch keyways and two setscrews as Dutch keys , in addition to the rectangular keyway . The Dutch keyways are threaded only on the alternate hub side or shaft side , with a thread clearance hole form on the opposite side . By simply driving setscrews into selected holes , the hub mechanism conveniently operates to rigidly lock or definitely release from the shaft , without hammering or hub - pulling . QD ( quick disconnect ) bushings work similarly , but place a circular pattern of three unthreaded and three fully threaded holes further out from the shaft axis on a bushing flange , instead of across the bushing - to - hub interface . A Hirth joint is similar to a spline joint but with the teeth on the butt of the shaft instead of on the surface . Saddle keys ( edit ) These types of keys are generally attached to the driving member ( e.g. shafts ) . These types of keys have less strength as compared with the sunk keys . These are rarely used keys , to transmit lower power to the driven members ( e.g. couplings ) Tangent keys ( edit ) Tangent key : these keys are used for the large heavy duty shaft . According to the name these are tangential to the shaft . These can withstand only torsion of one side of shaft rotation . For reversible motion of the shaft another key is mounted at 90 ° or 120 ° of angle with each other . These may be wedge or rectangular or square shaped . it is fit in round hole Motoreta keys ( edit ) Spline key ( edit ) Main article : Spline ( mechanical ) This types of key we use more than one keyways in hub / boss to transmit high power. Hence more than one key is used to connect hub from shaft in case of spline key Keyseating ( edit ) Keyseating is the creation of the slots in the mating items . Keyseating can be done on a variety of different machines including a broach , a keyseater , wire - cut EDM , a shaper or vertical slotting machine , either a vertical or horizontal mill , or with a chisel and file . Keyway cutters Special cutters Slotting tools Different slotting tools Broaching ( edit ) Broaching is primarily used to cut square cornered internal keyways . The specific broach , bushing and guide are used for each given keyway cross-section , which makes this process more expensive than most of the alternatives . However , it can produce the most accurate keyway out of all the processes . There are three main steps in broaching a keyway : First , the workpiece is set on the arbor press and the bushing is placed in the opening of the workpiece . Next , the broach is inserted and pushed through , cutting the keyway . Finally , shims are placed between the bushing and the broach to achieve the correct depth necessary for the key . Keyseater ( edit ) A keyseater and a sample of various shapes that can be cut Modern keyseating machine Keyseaters , also known as keyseating machines and keyway cutters , are specialized machines designed to cut keyways . They are very similar to vertical shapers ; the difference is that the cutting tool on a keyseater enters the workpiece from the bottom and cuts on the down - stroke , while the tool on a shaper enters the workpiece from the top and cuts downward . Another difference is a keyseater has a guiding system above the workpiece to minimize deflection , which results in a closer tolerance cut . The process starts by clamping the workpiece to the table with a fixture or vise . The workpiece is properly located and then the reciprocating arm is started . Some models have a stationary table so the cutter is fed horizontally into the workpiece , while others have a movable table that feeds the workpiece into a fixed cutter . These machines can cut other straight sided features other than keyways ( see the picture ) . They can also produce blind slots , which are slots that do not extend through the whole workpiece . Wire - cut EDM ( edit ) Wire - cut electrical discharge machining ( EDM ) is primarily used for small production lot sizes where either extreme precision is required or other cutting technologies are not readily available . Wire - cut EDM cuts keyways by eroding material away from the workpiece through a series of rapid electric current discharges between a spooling wire and the workpiece through a dielectric liquid . Computer numerical control ( CNC ) wire - cut EDM machines allow for a wide variety selection of keyways to be cut , inclusive of multiple keyways on the same hub . The main limitations of CNC wire - cut EDM is the time it takes to cut a keyway as well as the size of parts a given wire - cut EDM machine can accommodate . Shaping or slotting ( edit ) Shaping or slotting is largely used for cutting keyways that do not extend through the full length of the part . Like keyseating , shaping uses a single - point cutting tool for cutting , however , shapers are not guided through the cut on a fixed post . As such , shaper cuts are generally more susceptible to deflection than keyseater cuts . Milling ( edit ) Parallel , tapered , and Woodruff keyways can be produced on a milling machine . End mills or slotting cutters are used for parallel and tapered keyways , while a Woodruff cutter is used for Woodruff keyways . For internal keyways that are not too long , the keyways can be milled if a radius is acceptable . Chiseling ( edit ) One of the earliest forms of keyseating was done by chiseling . The keyway is roughed out using a chisel and then filed to size ; the key is tried frequently to avoid over filing . This technique is long , tedious , and rarely used anymore . Keyed joints ( edit ) A shear key is a feature intended to fail and avoid further damage should the machinery be accidentally operated in excess of its design limits . Shear keys may be any of the designs described above , but are made from a weaker material than the shaft . The shear key is easily and inexpensively replaced , and avoids more serious damage to the mechanism that would be costly or difficult to repair . For example , a steel shaft and pulley may employ a brass key . When excessive torque is applied to the joint , the steel edges shear the brass key into two pieces , leaving the pulley spinning loosely on the shaft and relieving the rest of the machine from possible damage . Two parallel keys can be used if the shaft connection requires a higher torque rating . Improperly machined keyways that had cutter deflection or drifting occur , may not be strong enough for the required application . See also ( edit ) Coupling References ( edit ) Jump up ^ Bhandari , V.B. ( 2007 ) , Design of machine elements ( 2nd ed . ) , Tata McGraw - Hill , p. 340 , ISBN 978 - 0 - 07 - 061141 - 2 . Jump up ^ Leonard 1908 , p. 394 . ^ Jump up to : Keys and Keyways ( PDF ) , archived from the original ( PDF ) on 2010 - 03 - 19 , retrieved 2010 - 03 - 19 . Jump up ^ Shigley , Joseph ; Mischke , Charles ( 1989 ) , Mechanical Engineering Design ( 5 ed . ) , McGraw - Hill , ISBN 0 - 07 - 331657 - 1 . Jump up ^ Garfield , Eugene ( 2007 ) . `` The John Scott Award Recipients from 1826 - present '' . Retrieved 2007 - 08 - 23 . Jump up ^ Krar , S.F. ( 1983 ) . Machine tool operations . ( pp. 84 -- 85 ) . New York : Gregg Division McGraw - Hill . Jump up ^ Keyseating , retrieved 2010 - 01 - 30 . Jump up ^ Wick , C.H. ( 1964 ) . Versatility of keyseating . Machinery ( NY ) , 70 ( 8 ) , 138 - 140 . ^ Jump up to : Cutting Keyways - Broaching , Keyseating , Wire - Cut EDM , Shaping , & Milling , retrieved 2014 - 12 - 03 . Jump up ^ Kibbe , R.R. ( 1995 ) . Machine tool practices . ( 5th ed. ed. , p. 572 ) . Englewood Cliffs , New Jersey : Prentice - Hall , Inc . Jump up ^ Leonard 1908 , p. 40 . Jump up ^ Romig , J.V. ( 1926 ) . The Popular Science Monthly . The Popular Science Monthly. , 110 ( 5 ) , 72 , 124 . Bibliography ( edit ) Leonard , W.S. ( 1908 ) . Machine - shop tools and methods . ( 7th ed. , pp. 39 -- 42 ) . New York : John Wiley & sons , inc . External links ( edit ) Wikimedia Commons has media related to Keys and keyways . Standard Metric Keys & Keyways ASME recommended key sizes for inch based units What is keyseating ? Key joint article from the 1979 Great Soviet Encyclopedia . Drawing and standard dimensions of keys Gardette Retrieved from `` https://en.wikipedia.org/w/index.php?title=Key_(engineering)&oldid=828862093 '' Categories : Hardware ( mechanical ) Mechanical power transmission Talk Contents About Wikipedia Azərbaycanca Български Català Čeština Deutsch Español Français 한국어 Hrvatski Italiano ಕನ್ನಡ Қазақша Nederlands 日本 語 Polski Português Русский Slovenčina Srpskohrvatski / српскохрватски தமிழ் Українська 12 more Edit links This page was last edited on 5 March 2018 , at 05 : 13 . Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply . By using this site , you agree to the Terms of Use and Privacy Policy . Wikipedia ® is a registered trademark of the Wikimedia Foundation , Inc. , a non-profit organization . About Wikipedia
1. Machine element used to connect rotating machine elements to a shaft
2. Types of keys: sunk, saddle, tangent, round, and spline
3. Keyseating: broaching, keyseater, wire-cut EDM, shaping, milling
4. Shear keys: feature intended to fail and avoid further damage
5. Keyed joints: shear keys, parallel keys, reversible motion keys