Riveting is done by (1) hydraulic riveting machines, both stationary and portable; by (2) portable pneumatic riveters, and by (3) hand hammers. Portable hydraulic riveters are massive and must be carried and held in place for their work by a crane.

Fig. 234 shows a type of powerful stationary hydraulic riveter. This is used to rivet the shell plates together and to rivet one head in the shell. The shell is suspended, with its axis vertical, by chains attached to a crane which is a part of the equipment of this machine. The riveting dies, closed together in the view, are opened to allow work to be suspended in the gap between the two arms of the machine, the arm on the right projecting up inside the shell. The die is placed as high on the right arm as possible to allow it to be used in riveting boiler heads and other flanged work. The hydraulic cylinder is so arranged that three different pressures, 50, 100 and 150 tons, may be exerted on rivets of various sizes. The men who operate the machine stand on a platform, not shown, built near the top of the arms. Heated rivets are passed up from a small furnace at the base of the machine.

Fig. 235.

Portable pneumatic riveters are much used for bridge, ship and boiler work. They are held in the hands of the workman and may be operated in confined spaces too small even for driving rivets with hammers. These machines are supplied by air at a pressure of about 60 pounds per square inch, led through a hose from an air compressor. Rivets are held in place while driving by a man or boy who presses a sledge hammer or other mass of iron, suitably supported, against the rivet head. Pneumatic holders-on are also used for this purpose.

Careless or fraudulent work in laying off and drilling rivet holes will bring about a lack of coincidence of two holes as shown at B in Fig. 235. If the relative displacement is slight, it may be remedied by careful re-drilling or by reaming. A bad practice is to drive a tapered steel pin into the hole to enlarge it (called "drifting"), and then to put in, a small-bodied rivet to cover up the defect.