Fig. 2469.
The proper shape for pipe tongs depends upon the number of sizes of pipe the tongs are intended for, but in all cases the point at which the gripping point should be is about as shown in [Fig. 2469]. This enables the edge at a to enter the work and grip it. If this point of contact were nearer to c it would be apt to slip upon the pipe, whereas, were it farther towards b, it would present a less acute angle to the pipe, which would be apt to jam in the tongs.
It is obvious that, if the tongs be moved in the direction of h, the whole power applied to f acts to cause the edge at a to grip the pipe, and that the length from a to g has an important bearing on the grip of a to the pipe; because the nearer a is to g not only the greater the leverage of the leg f, but also the less a, with a given amount of movement of f on its pivot, endeavors to enter the pipe; hence the movement of a in a direction to grip the pipe is less in proportion to the movement of f, and has a corresponding increase of force. It follows then that the nearer the grip of a is to c, the less, and the nearer the grip to b the greater, its grip upon the pipe. But, by making the length of a such as to grip the pipe in about the position shown in the cut, there is latitude enough in the location at which it will grip the pipe to permit of the tongs being used upon pipe of a somewhat greater or less external diameter, increasing the availability of the tongs. Furthermore, if a gripped the pipe at or too near to b, it would be apt to indent it. The crown of the jaw d may be made to fit to the pipe or to be clear of it; for thin pipe, as solid drawn brass pipe, it should fit so that the pressure will not indent the pipe, but for strong iron pipe it is better to let it clear, which will not only afford a firmer grip, but will also better fit the tongs to take in different diameters of pipe. In some cases, as in adjustable pipe tongs, the jaw surface d is, for this purpose, considerably V-shaped, as will be seen presently.
It is obvious that as a grips the pipe automatically, the tongs may be moved through any portion of a rotation that the location may render most desirable. Pipe tongs are designated for size by the diameter of the pipe they are intended for; thus, a pair of inch tongs are suitable for pipe an inch in diameter of bore, the handles or legs of the tongs coming so close together that both can be readily grasped in one hand applied at their extreme ends. If, however, the tongs be applied to pipe of a larger diameter the legs will be wider apart, and one hand will be required to be applied to each leg to force them together. A complete set of pipe tongs, therefore, includes as many pairs as there are diameters of pipe, unless adjustable tongs be used.
Fig. 2470.
