Page:Popular Science Monthly Volume 38.djvu/606

588 metal. Thirty to fifty tons of metal are sometimes melted in such furnaces.

Among the machine tools used in rolling-mills those called by the general name of "shears" occupy an important place; these tools vary greatly in form and constructive detail, and are designed with especial reference to the work for which each is intended. Fig. 42 is an illustration of a common form of lever shear for cutting bar iron. The cutting knives are located at a b, and when the eccentric d is revolved by the rotation of the shaft on



which it is placed, it lifts the long arm of the lever c and causes the upper knife b to cut or "shear" past the lower knife a, thus dividing any bar of iron that may have been between the two knives.

Fig. 43 is a front elevation of a "shear" for cutting boiler plate, and Fig. 44 is an end view and transverse section of the same machine.

In Fig. 43 at g is seen a large mass of cast iron, to the lower edge of which is attached a long, inclined cutting knife, which is designed to operate in conjunction with a straight knife attached to the frame of the machine (the relative positions of the two knives are shown in Fig. 44 at h and i) to shear any sheet metal