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THE POPULAR SCIENCE MONTHLY 



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 de- 

 signed with especial reference to the work for which each is in- 

 tended. 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 



It ' W 



Fio. 44. End View and Transverse Section of Boiler-plate Shears. 



wnich 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 



