With the passing of the apprenticeship system and the introduction of the present method of employing unskilled labor on a piecework basis for assembling, careful inspection has become a necessity. Under these conditions, the only way in which the product can be held to the required standards is to make the component parts fit accurately. If the inspection is adequate, parts can be held to closer limits and cheaper labor can be used in the assembling process.
Believing that no reason can exist for failure to maintain standards of accuracy if the ratio of the number of men engaged in production to one inspector does not exceed 15 to 1, the officials of the Buick Company have worked out a system, similar in many respects to a budget, in which a certain ratio of production hours to inspection hours is allowed in each plant, the number depending upon the nature of the work and varying from about 10 to 1 in the engine plant to about 34 to 1 in the gray-iron foundry. In actual operation these ratios were usually reduced.
The inspection department is divided into four divisions, each of which is under the jurisdiction of a divisional inspector who reports directly to the general superintendent. All major parts are given 100-per cent inspection. Parts purchased from other companies are given 10-per cent inspection, but if any are found faulty all are checked.
The process of inspection is followed from the time the incoming raw material is checked for quality by the metallurgical department, as it passes through the various steps of production, until it reaches the final assembling line. In general, inspection by pin and snap gages of the go and no-go type has been found most satisfactory, because this method gives quicker inspection and establishes definite limits beyond which parts are not allowed to pass.
Many of the testing devices employed are similar to those in common use in the industry but others have been specially devised to meet particular needs. Several of these containing noteworthy improvements are described in detail and illustrated. Extensive application is made of spark testing, both of the raw material and of parts coming from the heat-treatment. By this method not only can steels that may have become mixed be readily sorted, but the carbon-content and the presence of inclusions can be quickly and accurately determined, and the percentages of nickel, chromium, tungsten and vanadium present in an alloy-steel can be fairly closely estimated. Among the special devices described are those for inspecting crankshafts, cylinder bores, flywheels, camshafts, differential carriers, steering-knuckles, universal-joint yokes, chassis springs, the inside diameter of steel flywheel rings, wheel felloes, and the toe-in and camber of axles.