Editing Locomotive frame (section)

==Types of frame==
[[image:Dukedog.jpg|thumb|Preserved GWR 9017 showing outside frames]]
Three main types of frame on steam locomotives may be distinguished:<ref>{{Ransome-Wallis Encyclopedia}}, p 255.</ref>

===Plate frames===
These used steel plates about {{convert|1|-|2|in|1|abbr=on}} thick. They were mainly used in Britain and continental Europe. On most locomotives, the frames would be situated within the driving wheels ("inside frames"), but some classes of an early steam locomotive and diesel [[switcher|shunters]] were constructed with "outside frames".
Some early designs were '''double framed''' where the frame consisted of plates both inside and outside the driving wheels. Others were ''sandwich frames'' where the frame was constructed of wood sandwiched between two metal plates.

===Bar frames===
[[image:Bar frames U class locomotive WAGR.jpg|thumb|Bar frames of a [[WAGR U class]] locomotive]]
These are openwork girder structures built up from steel or iron bars which are usually {{convert|4|-|7|in|abbr=on}} thick, welded into a single load-bearing assembly. They were first used on the [[Bury Bar Frame locomotive]] during the 1830s, and were widely used in nineteenth century American locomotives (including those exported to Australia and New Zealand; see [[The Vogel Era#Vogel railways|Vogel railways]]).

===Cast steel beds===
[[Cast steel]] locomotive beds were developed in the latter years of steam locomotive design in the United States, from where they were also exported to Britain and Australia.