Finney 'Duke' in 7mm - 9083 'Comet'

[28ten]

Talking of Bulldogs, I have a shot of 'Empire of India' at Winchester 1945. IMHO a Duke is rather more tricky than an M7, I built an M7 in just over three weeks and I thought it was a very straightforward kit once the research had been done

 

[Steph Dale]

IMHO a Duke is rather more tricky than an M7, I built an M7 in just over three weeks and I thought it was a very straightforward kit once the research had been done

Hehe, I suspect you're right ;-)  I'll allow two weeks then!

Actually I think the M7 is a delightful kit.  I'm looking forward to building the ones I've got in t'other room; 7mm this time too.  I just need to get my finger out and have a third crack at the patterns for the Drummond inside motion; then I can crack on with the T9s, L11, S11, L12s, 700 and M7s.

Well, maybe next year...

Steph

 

[Dog Star]

I may have mis-read things from the (very scatalogical) research I did for my 2251.  It soon became pretty obvious which locos had second-hand (Dean goods?) wheelsets (elliptical cranks in line with wheel cranks) and which had been built with new wheelsets (oval cranks opposite wheel cranks) - their balance weights were a good indicator.

With reference to my earlier post....  there is no reason why Swindon had to use "new" wheelsets for "new" construction, or at subsequent overhaul, provided that the intended wheelsets had the required tyre diameter, the axles had the required journal sizes and the crank throw was compatible with the cylinder stroke.  What intrigues me about your post is the implication that Deans Goods engines might have had the Stroudley arrangement for balancing of cranks....  must go and read the relevant parts of RCTS Locos of the GWR.

From this I 'leapt' to the oval crank being associated with Collett, but I agree it's equally likely to have just been a works development; the elliptical cranks certainly being earlier and harder to shape/machine (easier to 'strap' though!)

I am not sure that I understand what you mean by "easier to 'strap' ", please explain.

regards, Graham

 

[Steph Dale]

Graham,

I think that the Dean Goods and late Collett 2251 had wheels that were different in pattern - the crank was in line with the spokes on the Dean Goods and between on the 2251.  I wasn't sure I'd remembered that correctly so I've just checked a couple of references.  In any case, whether it's mentioned in the RCTS book or not; you can see from the position of the balance weights that the inside cranks are in different positions and that 2251s were probably built with both (all?) styles; depending upon the loco they seem to have both spoke/crank aligments and balance weights in both positions.

As regards 'strapping' cranks we're on to the problems that many early locos had as they were given higher pressure boilers and/or superheating with earlier ('legacy', if you will) elliptical cranks.  One solution to reduce the chance of a shifted or broken crank was to expand and then shrink a steel 'strap' around the crank, in much the same way as fitting the tyre on to a railway wheel.  This seems to have been relatively common on other railways using elliptical cranks; various LBSC (0-6-2 tanks when superheated), SECR (D1, E1, L 4-4-0s at least) and Midland (most of them!) locos seem to have had their cranks strapped in this way.  Though I have to say that I've not thought or investigated as to whether the GWR had the same or similar practise.  Maybe Swindon went straight to an oval crank...?

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...

Cheers,

Steph

 

[28ten]

The Dean goods did indeed have a different pattern to the 2251. Very broadly speaking the Dean and 517 shared the same pattern wheel ( only available from AGH) and the 2251 and 14xx shared a similar wheel and all are 5'2" diameter. The Slaters wheel is a fair representation of the later style, although you will find the AGH is more accurate.
I have a Dean Goods in the todo pile, but I have yet to turn up the wheel castings.

 

[Dog Star]

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

 

[Steph Dale]

Cynric,

I note that Slater's list two GWR pattern 5' 2" 16spk wheels; both have 10" stroke, 7862GW is pin between, 7862W is pin in line...

Graham,

The 30" stroke would have had a far from subtle effect upon the loco's motion parts, wheels and axles.  And that's before figuring in hammer blow or other forces...

Steph

 

[Dog Star]

The 30" stroke would have had a far from subtle effect upon the loco's motion parts, wheels and axles.  And that's before figuring in hammer blow or other forces...

Steph

I had pondered on the piston stroke and then concluded that I did not have the knowledge to expound on that aspect of the design changes.  Stars were 26" stroke whilst the Saints were 30" stroke (as were / are the 2800 class).  Maybe I ought to have a look at RCTS again and see about the outside frame 4-4-0 engines.

regards, Graham