AUTOMATIC MACHINE GAGING 729 



Sampling methods or percentage inspection are applicable to parts 

 that are made under conditions that may be considered approximately 

 uniform or, as a statistician would say, under "a constant system of 

 causes." Piece parts made in the punch press and screw machine 

 are good examples of this. Many other classes of operations, partic- 

 ularly those in which some part is manual, produce parts which are 

 not so uniform. As the variability increases, or as the requirements 

 for precision become more exacting, the possibilities of sampling inspec- 

 tion become less attractive. 



In many cases the conditions and requirements are such that only 

 detail inspection or gaging is satisfactory. 



In some instances automatic machine gaging of the entire output 

 will cost less than a sampling system in which there must be included 

 with the direct cost of inspection the cost of some additional super- 

 vision and control. 



The possibilities so far as designs are concerned seem almost un- 

 limited, so that the question of when to apply such methods becomes 

 purely an economical one in which the number of parts to be handled, 

 the difficulty, unpleasantness or tiresomeness of the operation, the 

 precision required, and the cost of suitable labor become the controlling 

 factors. 



Aside from the question of cost, it is often a matter of great satis- 

 faction to place an objectionable hand operation on the machine and 

 release the labor for more pleasant and useful work. 



