The forging of the separate semicircular bands of excentric rods consists in preparing and curving a straight bar which is of proper length, width, and thickness. (See Fig. 140.) If the bar is first well hammered and reduced while straight, after the band is curved to its form, the fibres will be in a suitable position for sustaining the strain while in ordinary use. After the piece is reduced to its width and thickness, the length of bar necessary for the band is equal to the lengths of the two bosses added to the length of the band's mid-semicircumference; and the length of the semicircumference is known by being half the length of the entire circumference of the band's mid-circle.

The bending or curving of the straight piece to a semicircle is accomplished by first heating a few inches of one end, and bending it to a few inches of the curves that are marked on the surface-table. The adjoining portions are afterwards successively heated and bent to the same lines, until a near approach to circularity is obtained.

For large bands it is necessary to provide thick cast-iron rings, to hang on the cylindrical pieces in the angular gaps. The bands are heated to a suitable heat, and then placed upon rings of suitable diameter, and bent by large top-tools, or by hammering.

A substitute for these rings consists of the conical filler that was mentioned for stretching slide-rod rings. While the filler is lying in a horizontal position, in a convenient place, the band or bands are held on that portion which is nearest to the diameter desired. While on the filler, the bands may be curved, and lengthened by hammering if necessary.