THE SECURING OF PISTON-ROD TO CROSS-HEAD.

In the early days of the horizontal engine, the old style forked connecting-rod was always used, because it offered in the form of cross-head (which was wrought iron) a sure and easy fastening for the piston-rod.

The hub to receive the rod was made twice the diameter of the rod; the hole was bored to a taper of one-half inch per foot, and the length of hub was three times the diameter of rod. The rod was turned at the end to an accurate fit for the taper in cross-head, with thread on extreme end. It was drawn to and held firmly in place by a substantial nut, fitted well to the thread on the rod. But the forked connection for horizontal engines has since been supplanted by the single end rod, and consequently the nut on the end of the piston-rod has been abandoned, by reason of the inconvenience of screwing it up to place, and because its use added a few inches length to the cross-head. This change of front was, at the time it was made, a great mistake, and was so pronounced by many engineers. At all events, there has never been a better fastening used since, although there are several other methods in use at this date.

The screwing of a piston-rod into a cast iron cross-head, with a jam nut at the back of the cross-head hub, is about the most unsatisfactory device in use, but some of the most extensive

manufacturers have constructed their cross-heads in this way for years. They fought against fate, however, in this matter of design, and we notice with pleasure their adoption of an old, but better plan. They now use either the double or single round end thin steel key. It is true that the key slot weakens the rod, but no more than the coarse V-threads they formerly used. By this latter plan the piston rod can be disconnected from the cross-head in one-tenth part of the time required in so doing with the screw arrangement, and there is no damage to the rod in either connecting or disconnecting when the key is used, while by the screw method the piston-rod thread is injured, more or less, every time it is removed from the cross-head. Then, in using the screw and check-nut fastening, the builders make their beds so narrow at the slides (the idea being compactness of design) that we have positive evidence that there are now in this country nearly two hundred engines, the piston-rods of which must be removed from the cross-head, and the crosshead removed from the slides and bed plate, before the cross-head pin brasses, and connecting rod strap can be taken out for examination or adjustment.

The above operation requires not less than one hour on a fifty-horse power engine, and the same time to replace the parts named. These facts lead us to the conclusion that the best way of

Pistons

making the piston-rod fast to the cross-head is by the old taper end design, with a wrought-iron nut, drawing the rod home against the taper, and a substantial shoulder. The nut can be cylindrical in form, as we now have several ways of screwing round nuts to a solid bearing in close quarters. Then the only change it makes in the cross-head is a few inches additional length. When the nut is in position, it is firmly fastened by a clip attached to the cross-head proper, and this precaution insures it against any liability of getting loose.

Piston rods should in all cases be made of machinery steel, well hammered. The allowance for turning from the rough bar need not be more than of an inch. Nothing is better adapted to the tensile and compressive strains of a piston-rod than the above-named metal. It is free to turn and finish, and polishes to a beautiful surface after a few weeks' running. The common, and perhaps the best way of securing the piston to the piston-rod is the shrinking process. It is certainly the cheapest; but one piece of machine work connected with this part must be done with great care-this is the boring of the piston head. The hole must be absolutely true. and of equal diameter throughout its whole length, in order to have a uniform and perfect grip on the rod when cold after shrinking.

Two years ago the writer repaired a twenty

inch cylinder engine, after a breakage from a loose piston. A few moments' examination disclosed the fact that the hole had been bored, by improper attention to the tool, of an inch tapering. The piston was seven inches deep, but had a bearing on the rod of only 15% inches; the riveting on the end of the rod being too slight to offer any resistance to the loose piston. It would have cost no more to have made this a perfect job, in the first place, but it cost two hundred dollars to make it a perfect one after the break.

PISTON AND STUFFING BOX PACKING.

Various arrangements have been used to diminish wear and consequent leakage, partly arising from the adoption of high piston speeds. In Europe, where the piston rod of horizontal engines often passes through both cylinder heads, and is guided by a cross-head at each end, the solid phosphor-bronze piston has sometimes been used in cylinders up to about sixteen inches diameter. These pistons generally have a thickness of one-fourth their diameter, made quite light and partly sectional for adjustment. They have a series of small grooves, four or five in number, turned in their edge; the grooves are supposed to be filled by condensation, these acting as packing; but this piston has yet to be thoroughly tried.

The English use a solid cast iron piston with two or three small square steel rings sprung into the edge, but with these lubrication must be sure and perfect, or trouble will at once be at hand from serious and rapid cutting; but the piston receiving the most favor from English engineers to-day for cylinders up to thirty inches diameter, is the one with two cast-iron rings turned eccentrically so as to have a difference of about four to one between the thick and thin sides. The thin side is tongued and grooved together, and is not less than 3% inch thick. Both rings are reinforced on the inside by steel bands, and are fitted carefully to a central junk ring; they give no trouble and are very substantial.

Self-acting steam packing for pistons has not a very strong foothold in any of the old countries yet, but the good packings will probably take their places there in due time, and this turns us to the subject of self-acting steam packing in this country.

During the past twenty-five years, many patents have been granted, covering different modes of effecting a steam packing. Some of these have been practically introduced, and have shown good results when properly cared for; and when we say this, we do not wish our steam packing friends to think we are writing down their mechanical principle. Far be it from our