430 APPLIED SCIENCE 



work, and rigid construction and stiffness are needed to take 

 the heavy cuts, as the surfaces of castings and heavy forg- 

 ings are usually hard crusts difficult to remove. In most 

 shops much of this rough cutting is saved by the use of a 

 pickling solution of one part sulphuric acid to eight parts of 

 water. This solution is painted over the casting, and after 

 four or five hours washed off with clear water, thus removing 

 the sand and hard grit from the surface. If the castings are 

 small, they are put with the pickling solution into a wooden 

 vat into which a small amount of steam is injected. The 

 castings are thus easily prepared for machining. 



For roughing cuts on a planer, a highly tempered diamond- 

 nosed tool is used which must be kept sharp by grinding. 

 The cut of the roughing tool should be deep enough to go 

 below the scale or surface, and thus allow the tool point to 

 reach soft metal. Care must be takeri not to allow the tool to 

 ride over the hard scale, without doing any work, as a heavy 

 drag on the machine will thus be caused. In cases where the 

 casting is out of level, it should be leveled as nearly as pos- 

 sible. In such cases several cuts will be necessary to get the 

 planer properly started. Any hard burr or sand-hole lump 

 on the surface of the casting is best removed by a chisel 

 and hammer, as an unnecessary strain is thrown on the 

 machine tools when an attempt is made to remove them by 

 planing. 



After the surface is smooth, the round-nosed tool may 

 next be used to plane to size arid to proper depth. Some 

 work may require no further finish than this. In cases where 

 a smoother finish is desired, a square or flat-nosed tool is 

 fed with a rapid revolution of the feed screw, sometimes as 

 much as one-fourth revolution per stroke of the planer 

 platen. The cross-rail is supplied with two feeding devices 



