Editing Railway turntable (section)

== History ==
[[File:1961 - Central RR Of New Jersey Roundtable and Locomomotive Yard.jpg|thumb|left|A turntable for the [[Central Railroad of New Jersey]].]]
[[File:09 Warehouses etc at the end of the Tunnel towards Wapping, from Bury's Liverpool and Manchester Railway, 1831 - artfinder 267568.jpg|thumb|left|Turnplates at the [[Park Lane railway goods station|Park Lane goods station]] of the [[Liverpool and Manchester Railway]] in 1831]]
Early [[wagonways]] were [[industrial railway]]s for transporting goods—initially bulky and heavy items, particularly mined stone, ores and coal—from one point to another, most often to a dockside to be loaded onto ships.<ref name=WelshAJR/> These early wagonways used a single point-to-point track, and when operators had to move a truck to another wagonway, they did so by hand. The lack of switching technology seriously limited the weight of any loaded wagon combination.<ref>{{cite book|title=Estates, Enterprise and Investment at the Dawn of the Industrial Revolution|author=David Oldroyd|publisher=Ashgate|date=13 Nov 2007|isbn=978-0754634553}}</ref>

The first [[railway switch]]es were in fact wagon '''turnplates''' or [[Railroad Switch#Stub switch|sliding rails]]. Turnplates were initially made of two or four pieces of wood, circular in form, that replicated the track running through them. Their diameter matched that of the wagons used on any given wagonway, and they swung around a central pivot. Loaded wagons could be moved onto the turnplate, and rotating the turnplate 90 degrees allowed the loaded wagon to be moved to another piece of wagonway. Thus, wagon weight was limited only by the strength of the wood used in the turnplates or sliding rails. When iron and later steel replaced stone and wood, weight capacity rose again.<ref name=WelshAJR>{{cite book|title=The Rails and Sails of Welsh Slate|author=Alun John Richards|publisher=Llygad Gwalch Cyf|date=16 March 2011|isbn=978-1845241742}}</ref>

However, the problems with turnplates and sliding rails were twofold. First, they were relatively small (often no more than {{convert|1|yard}} in length), which limited the wagon length that could be turned. Second, their switching capacity could only be accessed when the wagon was on top of them and still, which limited the total capacity of any wagonway. The [[railway switch]], which overcame both of these problems, was patented by [[Charles Fox (civil and railway engineer)|Charles Fox]] in 1832.

As steam locomotives replaced horses as the preferred means of power, they became optimised to run in only one direction for operational ease and to provide some weather protection.<ref name=WelshAJR/> The resulting need to turn heavy locomotives required an engineering upgrade to the existing turnplate technology. Like earlier turnplates, most new turntables consisted of a circular pit in which a steel bridge rotated. The bridge was typically supported and balanced by the central pivot, to reduce the total load on the pivot and to allow easy turning. This was most often achieved by a steel rail running around the floor of the pit that supported the ends of the bridge when a locomotive entered or exited. The turntables had a positive locking mechanism to prevent undesired rotation and to align the bridge rails with the exit track. Rotation of the bridge could be accomplished manually (either by brute force or with a [[windlass]] system), popularly called an "Armstrong" turntable,<ref>{{cite book| url=https://books.google.com/books?id=CxAXPWlW_6UC&q=armstrong+turntable&pg=PA41| via=Google Books| page=41| quote=A lever was installed at both ends of the bridge and the table was moved by hand, a method popularly called "Armstrong."| title=The Model Railroader's Guide to Locomotive Servicing Terminals| first=Marty| last=McGuirk| publisher=Kalmbach Books| year=2002| location=Waukesha, WI| edition=1st| isbn=0-89024-414-6}}</ref><ref>{{cite web| url=https://www.american-rails.com/turntable.html| title=Turntable| website=American-Rails.com| accessdate=January 31, 2021}}</ref> by an external power source, or by the braking system of the locomotive itself, though this required a locomotive to be on the table for it to be rotated.

The turntable bridge (the part of the turntable that included the tracks and that swivelled to turn the equipment) could span from {{convert|6|to|120|ft|m|1}}, depending on the railway's needs. Larger turntables were installed in maintenance facilities for longer locomotives, while short line and [[narrow gauge railway|narrow gauge]] railways typically used smaller turntables. Turntables as small as {{convert|6|ft|2}} in diameter have been installed in some industrial facilities where pieces of equipment are small enough to be pushed one at a time by humans or horsepower.

Some turntables that were built in earlier days rapidly became unsuitable for the longer locomotives introduced. [[Roundhouse (venue)|The Roundhouse]] in London was built in 1846 to turn around steam locomotives on the line to Birmingham, but newer locomotives were too long within ten years—the building has been preserved and used for other purposes over the years.<ref>{{cite web | last=Rose | first=Steve | title=Steve Rose reports on the restoration of the Roundhouse |newspaper=The Guardian | date=29 May 2006 | url=https://www.theguardian.com/artanddesign/2006/may/29/architecture }}</ref>