Typical dimensions of Mid 19th century locos

[andrewnummelin]

I have a couple of modelling projects in mind for which I only have some side elevations, so I started looking through my files and books and was surprised that some information needed was consistently missing!

With outside framed locos was there a typical dimension over the outside frames?
I've only 2 general arrangement drawings, and those are from late 19th century: the one was 6' 1/2" and the other 6'11" ! Scaling from diagrams produced estimates between 6'3" and 6'8 1/2". Clearly the width over the frames will depend on the arrangement of the axle box horns (inside, centred on, outside the frames) but this can't be determined from a simple side elevation.

Was there a typical width for driving wheel leaf springs?
I've results from scaling diagrams ranging from under 4" to 6" - considering the line widths in the diagrams the accuracy of these estimates must be very poor!

What were typical thicknesses of coupling rods (and outside cranks)?
Side views show rods to be much less "tall" than those of more modern locos, but were they thinner too?

[Jim Summers]

I am no expert, but Euan Cameron is, having studied in depth and drawn such locomotives for many years. So, from New York, where he now resides, comes the following authoritative information in response to Andrew's query.

I may add that Euan has supplied the beautiful drawings from which our fleet of elderly locomotives on Burntisland 1883 is based, and two more have just passed their trials last weekend.

Jim

So here are Euan's thoughts:

"Thanks for forwarding this. I'll respond quickly before getting down to work (it's still earlyish over here).
Outside frame widths were quite variable between locomotives and designers.
Much less variable was the distance between the centres of the bearings of outside framed engines. Assume:
back-to-back between wheels = around 4' 5 1/2"
back-to-front dimension from the back of the tread to the front of the boss = 6 1/4" or near enough
axlebox depth = around 9" for a driving axle, less for a carrying axle
This gives us a centre-to-centre for driving wheel outside bearings typically of 4 1/2" + 6 1/4" + 4' 5 1/2" + 6' 1/4" + 4 1/2" = 6' 3".

6' 3" is near enough typical for the 1860s and onwards. If the locomotive had outside frames only for the carrying wheels (the "Jenny Lind" arrangement) then the journals will be shorter and the centres more like 6' 2" apart (or even less in earlier examples). For example, the bearings of all Drummond and Holmes tenders were 6' 2" centres to centres throughout the last decades of the N. B. R.

Then one just has to look at the relationship between the bearings and the frames. Tenders typically had the frames very close to the wheels with the horns and axleboxes fully outside, so the outside of a tender frame may be around 5' 9" or a little more.

Some tenders and a few locomotives had the outside frames aligned exactly with the centres of the bearings, in which case the width of the outside frame equals the centres of the bearings plus the thickness of one frame. In such cases the spring hangers had to be divided, with straps running both sides of each frame. This is highly visible in photographs.

More typically the frames were somewhat outside of the centres of the bearings, with the spring hangers concealed; in those circumstances a fairly typical outside frame width may be around 6' 7" - 6' 8" or more. But if one works from a roughly standard centre-to-centre of the outside bearings and sees how the frames are constructed, one will not go far wrong.

Axle springs from this period were more usually 4" thick.

Outside cranks could be between 4" and 5" thick. Sometimes the throw was the same as the inside crank throw, sometimes a little less, as there was no reason why it had to be the same as the inside cranks on an inside cylinder engine.

Coupling rods will typically be around 3 1/2" thick at the hubs, but much less in the middle of the rod, sometimes as thin as 2" (this is not usually shown except in the largest-scale models, because it makes the rods quite weak in small scales).

There will of course have been exceptions; but these are my overall impressions from a few years of studying these matters".

[billbedford]

Wild Swan's Midland Engines No 4 The '700' Class has a book load of drawings for a MR Kirtley outside framed loco. And, like all the WS loco monographs, the drawings are all reproduce at 12mm:1ft, so scaling is easy.

The only quibble I have with Jim's dimensions is that later coupling rods tended to be 1.5 in thick. The difference may be due to the change from wrought iron to steel.

[andrewnummelin]

Jim,
Many thanks, and especially to Euan, for the detailed analysis that confirmed some of my guesses and explained loads more. This will be extremely useful for several projects that are on my wish list. As I've had help from the USA on the CAD program I am starting to use, the next loco will have significant American influence.

Bill,
Thanks for the mention of the Wild Swan book - I'll certainly be consulting it. Another loco on my wish list was apparently very similar to the Kirtley design, but it is a long way down the list and may never reach the top. Still it will be interesting to collect the information.





The one loco I've had the chance to measure (Mersey Railway 0-6-4T in Liverpool Museum) has the following dimensions:
Crank 5in thick at axle, 4in at crankpin
Plain coupling rod bosses 3.5in thick
Rod 2in thick by 4in deep
Joint boss 4in thick
Crankpin nut 5in diam by 1.5in thick


Hopefully I do a bit of drawing later today and start metal cutting tomorrow.

[Maitland]

The Manchester Science Museum Beyer Peacock collection has a lot of general arrangement drawings of early locos: here's a link to an 1860 Edinburgh & Glasgow Railway 2-2-2: http://emu.msim.org.uk/web/objects/common/webmedia.php?irn=15246.

And to a page around that period: http://emu.msim.org.uk/htmlmn/collections/online/imagescontact.php?QueryName=DetailedQuery&QueryPage=%2Fhtmlmn%2Fcollections%2Fonline%2Fdetailedsearch.php&col_ColTypeOfItem=Still+Image&col_ColCollectionName_tab=%22Beyer%2C+Peacock+%26+Co.+Ltd%22&Search=Search&StartAt=321

I also have (somewhere) some scanned GE drawings of early Vulcan Foundry locos which I can find if wanted.

[andrewnummelin]

The Manchester Science Museum Beyer Peacock collection has a lot of general arrangement drawings of early locos: here's a link to an 1860 Edinburgh & Glasgow Railway 2-2-2: http://emu.msim.org.uk/web/objects/common/webmedia.php?irn=15246.

And to a page around that period: http://emu.msim.org.uk/htmlmn/collections/online/imagescontact.php?QueryName=DetailedQuery&QueryPage=%2Fhtmlmn%2Fcollections%2Fonline%2Fdetailedsearch.php&col_ColTypeOfItem=Still+Image&col_ColCollectionName_tab=%22Beyer%2C+Peacock+%26+Co.+Ltd%22&Search=Search&StartAt=321

I also have (somewhere) some scanned GE drawings of early Vulcan Foundry locos which I can find if wanted.

Many thanks for the links - very useful indeed.
I wonder how the CSB experts would approach the 2-2-2 with its mix of inside and outside bearings.......
My project is a bit more straightforward being an 0-6-0T with outside bearings on all wheels - but I'm going to cheat a bit and not put 4 bearings on the centre axle!

[Will L]

I wonder how the CSB experts would approach the 2-2-2 with its mix of inside and outside bearings.......

While I appreciate you probably didn't really expect an answer, and much as I am unsure about being associated with the term "expert"...

Any form of suspension system is going to be interesting, and many will chose to go with fake outside frames.
Once were are there a CSB wire below the driving wheel and above the carrying wheels would be the way to go.

I have wonders about the right way to deal with 2-2-2s with CSBs, as "The Theory" says you should equalise the weight on each axle, while performance may well suggest it may be better to set it up so half the body weight turns up on the driving wheel. Interesting to try that and see if the worries about the loco oscillating round the centre axle are real or not.