It was proposed to estimate the accuracy of the hydro-cylinder cross-section shapes basing on the analysis of the circle diagram of their inner cylindrical surfaces, formed by the manufacturing operations, such as rough and semi-finishing boring and finishing paying-out, taking advantage of the method of deflection approximation from the circle by the Fourier’s trigonometric series in the gap [0, 2π].
Characteristics of the deflection dispersion of the radius-vector as the random value (average value, dispersion, amplitude spectrum) have been obtained for every circle diagram separately. It is proposed to present these characteristics as random values.
Dependences for finding mathematic expectation and dispersion for the lot of parts, machined at every of the available manufacturing operation, have been obtained for certain number of samples and circle diagrams, taking advantage of the small sampling theory, the method of rectangular engagement in particular.
The effectiveness of manufacturing operations has been estimated according to the Student and Fisher t-test. Availability of the advantageous or disadvantageous manufacturing heredity of the hydrocylinder cross-section shape has been found.
As the result of carried out experimental investigations and processing of the obtained statistic data on the inner cylindrical surface of the truck hoist crane hydrocylinder KTA-25, produced by the company “Drogobych truck crane plant” (Ukraine), the need to improve the manufacturing operation of the semi-finishing boring has been analysed.
