SECTION II 



METAL WORKING 



I. METALS. 



THE materials we have to make use of are chiefly : iron and 

 steel, brass, tin plate (" tin "), copper, and to a less extent, alu- 

 minium, platinum, zinc, and silver. 



As with wood, metals are used for their intrinsic properties, 

 not on account of cost ; rather, indeed, as in the case of 

 platinum, in spite of cost. 



The properties of these metals are generally better known 

 than those of woods. 



Cast Iron. This is a hard, brittle metal, of many grades 

 and qualities. The best " close grained " cast iron only is used 

 in making apparatus, and our experience of the metal will be 

 largely connected with repairs. Cast iron files easily and 

 cleanly, and drills well, but care must be taken when dealing 

 with thin pieces, owing to the brittleness of the metal. 

 Similarly when " tapping " a screw thread it should be re- 

 membered that from the same reason, threads in cast iron 

 easily " strip." 



Iron, especially in its purer form steel, being very sensi- 

 tive to the time-factor in cooling, is a somewhat troublesome 

 metal to deal with by means of heat, but as the manner and 

 methods of control become better known, it is soon found 

 that this property gives a much wider range of usefulness to 

 the metal than is possessed by any other. 



Cast iron, cooling first and most rapidly from the outside, 

 usually presents a very hard "skin" which is very difficult 

 to penetrate, even by a file, but once this is removed, the 



