Engineering reminiscences contributed to "Power" and "American machinist"

by Charles T. Porter

The first break in this monotony was made by Mr. Corliss, and was remarkable for the number and the radical nature of its new ideas. The cylinder was provided with broad feet near its ends, and was planted on the foundation. The pillow-block was provided with similar supports and was also secured to the foundation. The bed, so called, was a tie-beam uniting the cylinder and pillow-block, and not otherwise supported. It was of T section. The horizontal member was behind the center line of the engine, and was made very deep in the middle of its length to prevent deflection. The vertical member extended equally above and below the former and carried the guides, which were top and bottom V-grooves, between which the cross-head ran and the connecting-rod vibrated. The cross-head was provided with shoes fitting these V’s, and was adjustable vertically between them. The connection with the cylinders was made by a circular head supported by curved brackets. This connection was firm on one side only. The bed was reversible to suit right- or left-hand engines by merely turning it over.

In the bed for my engine, Mr. Richards struck out another design, which avoided some objections to the Corliss bed. The guides were supported from the foundation, and the connection with the cylinder was more substantial, but the reversible feature had to be sacrificed.

Mr. Richards’ bed, shown in the [illustration] facing page 70, was designed in the box form, the superior rigidity of which had been established by Mr. Whitworth. It was a box closed at the top and flanged internally at the bottom. It rested on the foundation through its entire length. The main pillow-block was formed in the bed, as were also the lower guide-bars. The cylinder was secured on its surface in the old-fashioned way.

Engine Bed Designed by Mr. Porter. Engraving made from an Old Print.

It occurred to me that the best features of the Corliss and the Richards designs might be combined to advantage. This idea I worked out in the bed shown in the accompanying [illustration], taken from a circular issued by Ormerod, Grierson & Co., of Manchester, and which was made from a photograph of an engine sent by that firm to the Oporto International Exhibition in 1865. It will be seen that this is Mr. Richards’ bed with the cylinder bolted to the end after Mr. Corliss’ plan. The great strength of the bed enabled the supports under the cylinder to be dispensed with. This left the cylinder free to expand by heat, and made it convenient to attach the steam or exhaust connections or both underneath. This bed has remained without change, except in one important respect. I made the first cylinders with a bracket which was keyed up from the base of the bed. In the [illustration] a corner of this bracket appears. At the Paris Exposition in 1867 Mr. Beyer, of the firm of Beyer & Peacock, the Manchester locomotive-builders, when he saw it, told me I did not need that bracket. I then left it off, but found the cylinder to wink a little on every stroke when the heavy piston was at the back end. To find the weak place, I tried the following experiment on an engine built for the India Mills in Manchester. I filed two notches in the edges of the brackets on the bed, opposite each other and about ten inches forward of the head, and fitted a piece of wire between them. This wire buckled very decidedly on every revolution of the engine, when the piston was at the back end of its stroke. I then united these brackets into a hood, and lengthened the connection with the surface of the bed, as it is now made. This affords a perfect support for the cylinder. Experiments tried at the Cambria Iron Works on a cylinder of 40-inch bore and 48-inch stroke, with a piston weighing 3600 pounds and running at 100 double strokes per minute, showed the back end of the cylinder standing absolutely motionless. This experiment will be described hereafter.

Cross-head Designed by Mr. Porter.

The cross-head which I designed at this time has always interested me, not only on account of its success, but also for the important lesson which it teaches. I abolished all means of adjustment. The cross-head was a solid block, running on the lower guide-bars if the engine were running forward, as was almost always the case, and these guide-bars were formed on the bed. The pin was of steel, with the surface hardened and ground truly cylindrical, set in the middle of the cross-head, and formed with square ends larger than the cylindrical portion. These were mortised parallel into the cross-head, and a central pin was forced through the whole. The flats on the pin I afterwards copied from a print. These prevent the formation of shoulders at the ends of the vibration of the boxes. I would like to know to whom we are indebted for this valuable feature. Every surface was scraped to absolute truth. The lubrication was internal, as [shown]. There are many of these cross-heads which have been running at rapid speeds in clean engine-rooms from twenty to thirty years, where the scraping marks on the lower bars are still to be seen.

The lesson is a most important one for the future of steam engineering. It is this. Two flat cast-iron surfaces, perfectly true and incapable of deflection, with the pressure equally distributed over a sufficient area, protected from dirt and properly lubricated, will never have the clean film of oil between them broken or even varied in thickness, and will run together without wear perpetually and at any speed whatever. The conclusion is also abundantly warranted that a tendency to heat need not exist anywhere in even the least degree, in engines running at the greatest speeds. This can always be prevented by truth of design and construction, and the selection of suitable material. This fact is abundantly established by varied experience with cylindrical as well as with flat surfaces, and for other materials, though not for all, as well as for cast iron.