The manufacturing accuracy for case parts is dependent to a considerable extent on the errors in attaching the components, which may be equal to or sometimes larger than the assembly errors. The attachment error is affected by the following systematic and random factors: relief in the contacting surfaces of components; rigidity in them; contact rigidity of joints in a system in the direction of action of the mounting forces; number of mounting forces; action of those forces at different times on the components, and so on. Those factors in mounting components result in a system of active and reactive forces and moments, which always differ from the calculated values. A major factor causing mounting errors is the relief of the contacting surfaces of fittings and components. In the design, these surfaces are considered as geometrically regular and ideal, while the active and reactive forces acting on the components on mounting are taken as corresponding to the scheme in Fig. 1. However, the more the relief of the actual surfaces differs from the relief of the ideal ones, the more the actual forces differ from the calculated ones.
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