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E.P. Allis 3000hp Quadruple Expansion Corliss Engine, 1893 in 1/12 scale

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bananarchy:
Introduction

Here begins what will be a very long and daftly ambitious undertaking, but something that, when reduced to its individual elements, at least appears to be feasible. Some years ago, I happened across mention of this engine in Wonders of Machinery Hall, an account of one of the main exhibits of the 1893 World's Columbian Exhibition in Chicago. There was all manner of fascinating engines and manufacturing equipment, but one in particular stood out. This was purported to be the largest mill-style engine ever built, at least at the time, and was used to drive dynamos and generate electricity for the fair. The cylinders measured 26", 40", 60" and 70" with a 72" stroke, and the engine ran at 60rpm.

Even more interesting than the quadruple-expansion setup and the massive scale of the engine, though, was the valve mechanism. I managed to find an original copy of an arrangement drawing from a period publication, and noticed that in addition to the regular eccentric which drives the wrist plate as usual, there is a second, smaller one which feeds into the governor linkage somehow. Strange! More detail about that in a subsequent post, as it needs a bit of a treatise all on its own.

Over the course of the last couple years, I got involved with an organization that has iron foundry capabilities, plus some machine tools, and I also managed to acquire and set up a machine shop of my own (something I've been fantasizing about since I was a teenager). I had started modeling the engine in solidworks, partly for giggles and partly to try and reverse engineer the valve mechanism. A few months back, I realized I actually had all the resources and capabilities necessary to take a stab at really making this thing.

bananarchy:
The Miniature

So if we're going to build it, the next question is, how big? The answer, effectively, is as big as possible. I just like big engines to begin with, but additional scale also allows things to run more slowly and more smoothly, and be able to do real work. Also, one of the most interesting aspects of this engine is the trip gear and all the associated fiddly little linkages. I would like those parts to be scaled to the rest of the engine as closely to real practice as possible, and making everything bigger makes those parts more practical. The big parts can't be too big, though.

The determining factor ends up being the flywheel - this will be made as an assembly of castings, just like the real one, and it must be turned as a finished assembly. I have access to an Axelson lathe with a maximum swing of 30 inches, and the flywheel on the original was 30 feet in diameter, so bam. 1 inch to the foot. Perfect. At that scale, the trip gear parts are small, but totally doable, and a good bit bigger than plenty of things I've worked with professionally (I design robotic surgical instruments).

The engine will drive two dynamos with two concentric belts, which will allow load to be put on the engine to demonstrate the operation of the governor and trip gear under varying loads, and allow the compounding to properly work (or as much as it can without the vacuum from a condenser). Including the dynamos, the model will be about ten feet long, and the cylinders are 2.125", 3.3", 5.0" and 5.8" with a 6" stroke. The flywheel will be 30" in diameter and 6" wide on a 1.75" diameter crankshaft, and will weigh a bit under 200 pounds when finished.

The large bits are pretty much sorted, design-wise. There's still a fair bit of detailed design work to be done on the trip gear, and the governor will be a whole project in itself. The flywheel, though, is straightforward to design, and is a nice self-contained project, so that's where I'm going to start.

peatoluser:
Looking forward to following this build.
I notice the drawing is from 'The Engineer'. By chance I have a pdf from the rival periodical 'Engineering' that covers the same engine and you're right, from the description, it is a complicated valve arrangement!   
Good luck with the build

crueby:
Looks like an excellent engine to model!  Will be watching along...   :popcorn: :popcorn:

Sanjay F:
Wow - what a feat of engineering the original is and so too will be the model. 30" flywheel, that's going to be something to behold!

Very best of luck with it and I'll be following along intently!  :popcorn: :ThumbsUp:

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