THE L3 SYSTEM — QUALITY CONTROL IN MANUFACTURE 999 



the ends of the rods at the same time to permit easy insertion of the grid 

 in the support micas. Initial production was measured with a barrel 

 micrometer read to the nearest 0.0001". The resulting data indicated 

 a standard deviation of 0.00013". The 3-sigma limits of d=0.00039'' were 

 four times the desired spread. Some portion of this spread was undoubt- 

 edly due to the measuring instrument which could not be read with 

 sufficient precision. Subsequent production was measured with a Brown 

 and Sharpe dial indicating barrel micrometer which was calibrated with 

 standard gage blocks. Production measured under these conditions indi- 

 cated the standard deviation to be 0.00007" for process limits of 

 itO.0002". Fortunately, correlation studies indicated this tolerance to be 

 acceptable. Control charts are kept on the product after the tumbling 

 operation. The desired average is maintained by sampling the side rods 

 for diameter several times during the tumbling operation. 



The lateral wire used in winding the control grid is tungsten, etched 

 to a diameter of 0.00029" ± 0.00001". The diameter of the wire is 

 measured with a Bausch and Lomb metallurgical microscope equipped 

 mth a Filar eyepiece. The magnification used is approximately 450 X. 

 During initial production, it was not certain that wire of this size could 

 be obtained consistently to a given nominal value and a chart was pre- 

 pared adjusting the specified winding turns per inch to accommodate 

 wire sizes from 0.00027" to 0.00032". 



Control charts kept on the wire diameter have shown that it is possible 

 to make mre consistently to a diameter of 0.00029 =t 0.00001". Correla- 

 tion studies have been made comparing grids of various wire sizes and 

 corresponding turns per inch against the related tube characteristics. 

 From these studies it was determined that with wire controlled to 

 0.00029" d= 0.00001", a single winding pitch for each tube could be 

 substituted for the chart of turns per inch originally used. Subsequently, 

 studies were made which enabled a common grid to be used in the 436A 

 and 437 A tubes. 



After winding, the grids are gold plated. The desired increase in lateral 

 wire diameter as a result of plating is 20 micro inches with limits of =blO 

 micro inches. This measurement is also made with the microscope 

 equipped with a Filar eyepiece. 



Considerable difficulty has been encountered with measurement of 

 wire diameter. Variations between operators have been encountered as 

 well as differences between successive readings made at the same point 

 on the wire. This difficulty has been minunized by careful training of 

 the operators and by taking several readings at each point and averaging 

 them. 



