The firm of E. P. Allis & Co. of Milwaukee, exhibited a sawmill. This exhibit consisted of two large circular saws, each driven by a horizontal engine. The two engines were united by a common shaft on the ends of which the cranks were set at right angles with each other. The center lines of these engines were nearly 20 feet apart; the shaft carried two belt drums 8 or 10 feet in diameter, one of them near to the bed of each engine; at the middle of the shaft was a fly-wheel about 16 feet in diameter. The rim of this fly-wheel was in eight or ten segments, with an arm attached to the middle of each segment; the segments were bolted together and the arms were bolted to a hub on the shaft. The saws were set behind the cylinders, and the belts were carried from the drums on the shaft past the cylinders to smaller drums on the saw arbors. On starting these engines the two bearings of the main shaft heated so badly that the engines had to be stopped. The gentleman in charge of the exhibit applied to me for advice. I told him that although his shaft was large it was long, and the weight of the fly-wheel bent it so much that the two journals ran on the inner edges of their bottom boxes, which caused the heating. I told him he did not need the fly-wheel at all; the cranks being quartering, the momentum of the belt-drums was amply sufficient to maintain uniform motion, and I advised him to take off the fly-wheel. This he did at once, leaving only the hub on the shaft; the engines then ran with cold bearings and uniform motion throughout the exhibition. They had made a cut-off gear for these engines, but it was found not to suit the purpose and was taken off. This firm then did a great stroke of business: they came to the sensible conclusion that they could do a great deal better than to attempt to work out a new system of engineering for themselves, so they offered to Mr. Edwin Reynolds, the manager of Mr. Corliss’ works, and to his head draftsman, inducements sufficient for them to leave Mr. Corliss’ employment and take the same positions in the Allis works at Milwaukee for the manufacture of the Corliss engine there. With the magnificent result of this action the engineering world is familiar.
We had all sorts of queer experiences. One day I was demanded by Mr. Jerome Wheelock to tell him why the engine exhibited by him was not a perfect engine. I glanced over the long slender bed, a copy of the Corliss bed without its rigidity, and declined to answer his question. Mr. Emery was more compliant; on receiving the same demand, he kindly pointed out to Mr. Wheelock one respect in which his engine could hardly be considered perfect; the steam was exhausted into a large chamber embracing the lower half of the cylinder from end to end. This comparatively cold bath produced the condensation of a large quantity of the entering steam. From the middle of this chamber a pipe took away the exhaust from the opposite ends of the cylinder alternately. Mr. Wheelock admitted the defect, and said in future he would avoid it, so, as I learned, having two exhaust pipes instead of one, he gave to each pipe one half the area of the single one.
I had the pleasure of renewing my acquaintance with Professor Sweet, who was superintending the exhibit of the mechanical work of his boys at Cornell; this was very creditable and included quite a show of surface plates.
The Corliss engine in this exhibition was far the most imposing, and to the multitude the most attractive single exhibit ever shown anywhere. It consisted of two distinct engines, each having a cylinder 40 inches in diameter, with 10 feet stroke of piston, the motion of which was transmitted through cast-iron walking beams to cranks set at right angles with each other on the opposite ends of a common shaft. This shaft made 36 revolutions per minute and carried a gear-wheel 30 feet in diameter; this wheel engaged with a pinion 10 feet in diameter on the line of shaft under the floor, giving to this shaft a speed of 108 revolutions per minute.
One day I said to Professor Sweet: “Do you know, Professor, that an engine with a single cylinder of the same bore as these and 5 feet stroke directly connected with a line shaft and making 150 revolutions per minute, with a fly-wheel 10 or 12 feet in diameter, would exert more power than is afforded by this monster and would run with far greater economy, because the internal surfaces to be heated by the condensation of the entering steam would be one piston instead of two, two heads instead of four, and 5 feet length of exposed cylinder instead of 20 feet?” He replied: “That is all very true, but how would you get the steam in and out of the cylinder properly with a piston travel of 1500 feet per minute?” I was not prepared to answer that question on the instant, but I afterwards found no difficulty about it.
The accompanying figures illustrate this engine and my high-speed equivalent drawn to the same scale; it will be seen that the small engine occupies about one tenth of the floor space needed for the large one, and would cost less than ten per cent. of the money. It would also have a more nearly uniform motion, the impulses received by the crank being 300 per minute, against only 144 per minute received by both cranks of the large engine, besides which in the latter the full force of the steam is exerted at the commencement of each stroke and falls to nothing at the end, while in the smaller engine, by the inertia of the reciprocating parts, the forces exerted at the opposite ends of the stroke would be practically equalized. The reader will doubtless inquire, as Mr. Green did why, with these enormous advantages, does not everybody use the high-speed engines and every builder make them?
The Corliss Engine Exhibited at the Centennial Exhibition.
Porter-Allen Engine Equal in Power to the Exhibited Corliss Engine.