188 BLACKSMITHING 



166. Tempering Steel. The greater the amount of car- 

 bon in steel, the harder it is, but the more ductile. The 

 amount of carbon in steel practically determines the purpose 

 for which steel may be used. Steel is hardened when heated 

 to redness and quenched in water or oil. 



When steel is heated and allowed to cool, naturally, it soft- 

 ens. It is upon this fact that tempermg, which is the process 

 of getting the proper combination of hardness and ductibility, 

 is based. As the hot steel cools, surface oxides are formed 

 which range from faint yellow thru straw, full yellow, brown, 

 purple and full blue to dark blue. The lightest of these colors 

 indicates the highest degree of hardness. 



Machine and Tool Repairs 



Under this heading is considered such work as one may be 

 called upon to do in constructing tools and machines made of 

 iron or steel, and which does not require the heating of the 

 metal. For the most part, such work will be done with hand 

 tools, as hammer, chisels, files, drills, taps, dies, rivets, etc. 

 Work which requires the careful shaping or fitting of cold 

 metal will need to be done in a machine shop and is not con- 

 sidered here. 



Tools and Equipment 



For general use about the premises, a small out-building or 

 room should be equipped with the following: 



One wooden bench made of well-braced 2" x 4" uprights 

 and stringers covered with plank and fitted with a spring 

 screw vise, or machinist's vise. 



One hand forge and anvil, with the common forge tools. 



