Heavy piston-rods are lined and centred while they hang suspended from a crane, either callipers, a straight-edge, or a rectol, being employed and used in the same manner as described for centring axles. A piston-rod having at one end a conical part with the large end of the cone at the rod's extremity, should be forged with a short holder or handle, this being a stem or superfluous piece solid with the rod. This holder is produced by thinning the rod's superfluous end at the conclusion of forging, and is necessary for the convenience of having a carrier fixed to it for rotating the rod while the cone is being turned, and also while the adjoining screw is being made. If a carrier is fixed to this handle at the beginning, the entire rod can be turned and screwed without the need of reversing it end for end in the lathe. The handle will also support a drift, which will be hammered against the outer end of the cone while being fitted to the piston.

Piston-rods, small and large, are made of steel, because of its hardness and consequent non liability to wear; but whether a rod of this shape is steel or iron, tbe order of its turning is about the same in any case. The entire rod is to be first rough-turned, so that the cone, the parallel part in the middle, and the small end are very near to the specified diameters; the middle part, at this turning, being made small enough to pass through the smallest part of the hole in the piston. The rod's cone is to be now finished to fit the piston. If the rod is being entirely turned without reversing it end for end, it is necessary to re-fix the gripper to the same position on the handle or stem, after every time it may have been removed to try the cone; because through the centre recess at the conical end being always on the mandril pivot, it cannot wear its surface to a proper bearing, and also because the mandril-pivot may not rotate truly.

To avoid the trouble of placing the rod into the piston several times during the fitting, the hole should be accurately measured with wire gauges, and the cone carefully turned thereto. Two gauges are required, one for the large end of the hole, and one for the small end; and their points are smoothly filed to gently fit their respective places, as described for the fitting of other wire gauges. The turning of the cone commences by reducing about a quarter of an inch of the cone's length at the small end, until its diameter is about an eighth greater than the length of the short wire. The length of the piston-cone is next ascertained, and marked upon the rod's cone by measuring from the short turned part at the small end. Consequently, if the length of the piston-cone is nine inches, a mark is made upon the rod's-cone at nine inches from the small end. The thick part of the cone is to be now reduced until its diameter at the mark is an eighth of an inch greater than the length of the long wire. This leaves an eighth of an inch to be turned from both ends of the cone, to make them of the specified diameter; and the two turned portions indicate the two extremities of a cone whose angle is about that which is required to fit the piston. And if the rough mid-portion be next reduced until level with the two extremities, the entire cone will possess the desired angle, although it will be an eighth of an inch too large in diameter.

The turning of the cone is effected while it is near the chuck, because the gripper is fastened to the stem; and to remove the metal the top slide of the rest is employed. This is adjusted to the proper angle, partly by means of the two turned ends. For this purpose, a pointer, or an ordinary front vee-tool, is fastened in the tool-holder, and the point is put opposite one of the short turned portions, and the exact distance between the tool-point and the turned surface is measured with an inside calliper. The pointer is now moved along, by rotating the screw of the top-slide until it is opposite the other turned end of the cone; and the distance between the point and the turned surface is measured with the calliper as before; and if not the same as while the tool was at the other end, the slide is shifted accordingly.

As soon as the slide-rest is arranged and the cone smoothly reduced thereby, each end of it is carefully measured, and the two gauges referred to, to discover in which direction the slide-rest is to be further adjusted to obtain the exact angle desired. By this means the entire cone will be accurately turned to fit the hole, and will also be situate at the required place in the hole when tried into the piston, if the turner has properly marked the length of the cone upon the rod, and has measured exactly at the two extremities when referring to the gauges.

For turning cones, two outside callipers are indispensable, one of which is adjusted to each wire, and lightly adjusted so that the legs may not be bent by pushing them tightly across the gauge-points. By attending properly to the measurements, a cone can be turned to very near the exact size and shape previous to removing it from the lathe to try it into the piston. Such cones are always forged with ample length for their respective holes; consequently, the exact distance to which the rod will enter is not important, the great requisite consisting in marking the cone's length upon the rod, and turning each extremity of it to its respective gauge.

When a rod is to be tried into a piston, the piston is stood edgeways between packing-blocks, and fastened thereto, either with bolts, wedges, or a screw-jack, that the rod may be inserted while horizontal. As soon as the rod is put in and pushed to its place, the long end is raised or lowered a short distance with the crane, until the rod's length is exactly square to the piston; at which time a few powerful sledge-hammer, or pendulum-hammer, blows are given to the outer end. To do this, a tubular drift is used, in one end of which is a hole large enough to allow ample room for the entire stem or handle of the piston-rod. This drift is attached to an ash handle, and is held on the stem while the blows are delivered. By this process, the cone of the rod is driven forcibly into contact with the piston-cone and marks are made upon the surfaces, which indicate the exact places of contact, and therefore show which portion of the rod's cone needs further reduction, and whether or not the slide-rest needs a slight alteration. At the trying-in the distance to which the rod enters is observed ; and if the cone has been finally fitted far enough into the hole, a mark is scribed upon the rod at each end of the hole. One of these marks will be required to show to what place the screw is to be cut, and the other mark will serve to show how much is to be cut off the outer or thick end of the cone, if any is to be removed from this part.

The next step is to cut the thread adjoining the cone. This thread is to fit a sort of cylindrical or ring-shaped nut of gun-metal, with which the rod is to be fastened in the piston ; which nut has been previously finished, being bored, screwed, and also, in some cases, turned to make its outside fit the recess in the piston. The length of the screw for this nut, or the distance along the cone to which it is to extend, is known by referring to the mark which was scribed upon the small end, at the time the rod was situate tight in its place in the piston. This mark is the place which will be occupied by the inner face of the nut when screwed tight against the bottom of the piston-recess ; therefore, a quarter, or three-eighths of an inch beyond the mark, is the place at which the thread is to terminate. The place for the thread being thus known, it is turned cylindrical at that place, and of a proper diameter to suit the already-formed thread in the nut. To ascertain this diameter, the outer diameter of the nut-screw is measured with a pointed wire gauge, made according to the instructions in page 351 for bolt-screwing. The cutting of the thread next proceeds while the nut is on the rod, or on the poppet-cylinder, in order that it may be accurately fitted upon the screw without removing the rod from the lathe. When the uut is screwed upon the rod to about the place it will occupy when in the piston, it appears as in Fig. 1124.

After the screw adjoining the cone is finished, the opposite end of the rod is turned to fit the crosshead, and also screwed, if a screw is intended. To mark the place for the crosshead-shoulder, the distance can be measured from the piston, or from the piston-nut, because these are finished. Turning of the mid-part exactly parallel is next performed, and is the last process. This is done by first taking off a thin slice along the entire length with a vee-point tool, and afterwards finishing it with a springy tool. To polish this portion and make it truly cylindrical, it is ground with a couple of wood grinders, or wood grinders having two pieces of sheet lead in contact with the part being ground, the grinders being supplied with emery and oil. But such a process is never requisite for a piston-rod; it is quite sufficient to smoothly file only the outer end of the parallel part, or to polish it with a springy tool. The remaining portion, which will be inside the cylinder, polishes itself by friction with the packing.