Steph Dale said:
This now seems to be turning into a slightly strange discourse; well into 'subculture of a subculture' stuff ;D Long may it continue; I'm learning a lot about Swindon's way of doing things as we go...
Steph
Maybe it is time that our Illustrious Leader moved things around a tad and used some of the material in Steph's thread to create a new thread in the Resources section... something along the lines of "interesting prototype questions of design"?
Your reference to shifting webs on axles has a corollary and it is relevant to GWR practice. All historians seem to accept that GWR Locomotive design practice went through a phase shift as Dean transitioned into Churchward and much of the latter's design practices/changes/improvements are documented in RCTS, Holcroft and Nock (with illustrations in GWRJ. One aspect of the changes which appears to have been not documented too well is the development of the basic coupled wheel. You have alluded to the appearance of the alternative strategies for balancing the motion on inside cylinder engines and our "histories" note the changes in the position of the crank pin, from being "in line" with a spoke (Churchward and ealier) to being "in between" spokes and a web between the pin and the rim (Collett and later) - yet none of the texts tell us why Stroudley balancing was thought to be necessary nor why the change in crank pin position. As to the later change, engineering good practices informs us that the crank pin between the spokes should give better support to the pin - so why was the change made so late in the life of the GWR DO? And was such a change really necessary for those "new pattern" driving wheels got used on "earlier" engines (and occasionally mixing "in-between" with "in-line" on the same engine)?
So where is this going?
Earlier this year I posed a question on RM Web and on the GWR E-list (a Yahoo Group) as to when and why did the GWR introduce a larger boss for the coupled wheels. The change in the size and shape of the wheel boss is enough that one can spot easily the "odd-man out" on an engine which has acquired a combination of early and late wheels. Photos of GWR engines in as near "as-built" condition indicate that the change took place just after the introduction of the Saint class. The initial Lots of Stars had the small boss whilst some Saints were built with the large boss so maybe 1907 or 1908 is the year when the large boss was introduced. Further, when an engine acquired a mixed set of small / large boss wheels at overhaul then the large boss would be fitted to the driving wheel in preference to either the leading or trailing axle, (although there are photos showing engines with a large boss on the leading and on the driving wheel).
As to why such a change was made, my best guess is that there was a spate of wheels shifting on the axle and those events were first encountered with the introduction of the Stars and Saints - after all, those engines were the first "bulk" builds of engines with large diameter wheels, outside cylinders and 225 psi boilers so maybe there was some lack of experience with the forces being exerted on the wheels. Given the divided drive of the Stars the finger seems to point to the early Saints as being the culprits. If wheels moving on axles was the underlying reason for the change then I am tempted to suggest that this change was accompanied by the introduction of a key into the wheel seat (the key is often visible in the end of the axle). If that is a reasonable assumption.... does that mean that Swindon did not key wheels to axles before that date? And what might that mean to the crank webs?
So, any one got any hypothesis on this change in design/workshop practices which gave us such a visual change in appearance of the beautiful Stars and Saints?
regards, Graham