I saw a reference to outside-frame steam locomotives today (narrow-gauge). This is not something I had been aware of.
I assume this means the drivers are inside the frame.
I looked around the web at photos, but none were clear enough to let me understand something.
Are the rods connected to some type of mechanisms (or discs) outside the frame that are connected to extensions of the drivers’ axles?
Obviously, I’m not talking about geared locomotives.
Usually, yes.
Look for pictures of the D&RGW narrow gauge 2-8-2s for this best illustrated.
https://upload.wikimedia.org/wikipedia/commons/c/c3/Colorado_-_Silverton_02.jpg
Wow. Thanks, NW!
That’s a great photo. Particularly when you zoom in on details. Very high res. I never came across any photos nearly this good.
That really shows well what’s going on.
I was reading about the D&RGW/D&SNG engines. I had no idea that some narrow-gauge locos were actually re-built from standard-gaugers. I wonder if when this was first done on a railroad, whether there were many clearance issues along the line that had to be dealt with. I’m guessing there must have been some.
Thanks.
The development pre-assumes that the North American-style adoption of a loading gage far outside nominal track gauge has been adopted.
At a certain point in anticipated locomotive design and power, to keep the frames ‘inside’ begins to become self-defeating, as larger bearings and stouter frames take up more space, and equalizing levers, brake rigging, and the like also need to stay accessible for maintenance. There are also questions of balance as the boiler gets bigger but gauge stays small on a railroad that likely has great line, surface, and cross-level anomalies.
So at some point it begins to make sense to adapt a perimeter frame to narrow-gauge engines, putting the bearings/journals outboard of the gauge entirely. If you understand how a tender truck with a Bethlehem auxiliary engine in it is arranged, you will have no difficulty picturing how the wheels are inside the frame but the cranks outside it. Now just add outside cylinders driving on a ‘normal’ main pin on one of those cranks.
Now, you could at this point reduce augment forces tremendously by adopting cranked axles and using inside rods, even adopting the dodge of putting one cylinder ahead of the other for clearance of larger bores – but this is self-defeating in terms of maintenance and assembly. It makes better overall sense, again, if you have the loading gage clearances, to just press crank webs on the outside of the axles, with pins that can be quartered normally with a machine, and apply rods to them.
Stability geometry is a bit better with the boiler weight imposed (via webs if nothing else) on the outside frame. Still ‘tippy’ but less dramatically proceeding to overturn.
There is a fairly dramatic progression here. For any kind of serious modern power on 3’ gauge, outside frames (as on the late D&RGW locomotives) are almost mandatory. For Cape gauge, which is only 6" wider, they are often unn
I omitted geared engines because it was easier for me to imagine how that would work. But seeing videos/pix of the conventional engines, I could see that the rods were on the outside, and I got curious.
As for clearances, I was wondering about track-side structures, etc., when now you have this wider engine, made from a standard-gauger. I am guessing it was not usually an issue, but I can imagine some situations (loading docks at freight stations?) where some modifications might have been needed.
I vaguely recollect that Cumbres Pass line improvements were done with the thought it might be converted to standard guage. The Farmington branch was originally built to standard guage.
In DRGW days, the K-36 and K-37 mikados couldn’t go all the way from Durango to Silverton. I think Rockwood was as far as they could go. After the line was sold, the new owners eventually did work (I think widening the Rockwood Cut and maybe some bridge work) to allow the bigger power to be used.
Jeff
Here is a good example:
Thanks. That shows it well.
Something that shows it even better is the clip recently provided in a different thread of the “Rock Island” scene from The Music Man.
Now, if someone had tried to tell me the CRI&P had outside-frame power in that era I would tell him he was full of beans. But seeing is believing! The power elite in Hollywood that made these movies, and paid through the nose for fact-checking minions populating long minutes of time in the credits, certainly wouldn’t lie.