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A trunnion (from Old French "''trognon''", trunk) is a cylindrical protrusion used as a mounting and/or pivoting point. First associated with cannon, they are an important military development.〔Keegan, John (1994). ''A History of Warfare''. Vintage. ISBN 978-0-679-73082-8〕 Alternatively, a trunnion is a shaft that positions and supports a tilting plate. This is a misnomer, as in reality it is a cradle for the true trunnion. In mechanical engineering (see the trunnion bearing section below), it is one part of a rotating joint where a shaft (the trunnion) is inserted into (and turns inside) a full or partial cylinder. ==Medieval history== In a cannon, the trunnions are two projections cast just forward of the center of mass of the cannon and fixed to a two-wheeled movable gun carriage.〔Duffy, Chris (1979) Siege Warfare: The Fortress in the Early Modern World 1494-1660. Routledge & Kegan Paul. ISBN 0-415-14649-6〕 As they allowed the muzzle to be raised and lowered easily, the integral casting of trunnions is seen by military historians as one of the most important advances in early field artillery. With the creation of larger and more powerful siege guns in the early 15th century, a new way of mounting them had to be specially designed. Stouter gun carriages were created with reinforced wheels, axles, and “trails” which extended behind the gun. Guns would be up to eight feet in length and shoot iron projectiles weighing from twenty-five to fifty pounds. These wrought iron balls when discharged were comparable in range and accuracy with stone-firing bombards.〔Duffy, Chris (1979). Siege Warfare: The Fortress in the Early Modern World 1494–1660. Routledge & Kegan Paul. ISBN 0-415-14649-6〕 Trunnions were mounted near the center of mass to allow the barrel to be elevated to any desired angle, without having to dismount it from the carriage upon which it rested. Some guns had a second set of trunnions placed several feet back from the first pair, which could be used to allow for easier transportation.〔Manucy, Albert (2008) Artillery Through the Ages. BiblioBazaar. ISBN 0-554-39597-5〕 The gun would recoil causing the carriage to move backwards several feet but men or a team of horses could put it back into firing position. It became easier to rapidly transport these large siege guns, maneuver them from transportation mode to firing position, and they could go wherever a team of men or horses could pull them.〔McNeill, William H. (1982) The Pursuit of Power. University of Chicago Press. ISBN 0-226-56158-5〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「trunnion」の詳細全文を読む スポンサード リンク
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