In this paper, the elastic approach between balls and ball races of the ball screw is discussed. The elastic approach quantity is deduced from the ball race profile equation reported in the previous paper, Hertz's elastic deformation theory and others.

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In lapping steel balls, we experimentally studied the effect of physical properties of lapping liquid on lapping quantity, sphericity and finished surface. For facilitating analysis of lapping liquid effects, we used, besides cast-iron lap, phenol-lap manufactured for tests which contains abrasive grains.
From the experimental result, we obtained following conclusions.
(1) Lapping quantity increased almost proportionally with increase of viscosity, but surface-tension effects were unnoticeable when it was below 35 dyne/cm.
(2) Lapping quantity varied with ratio of mixed abrasive grains, but the effect was unobserved upon sphericity and finished surface.
(3) We could discriminate the good or bad of finished percentage according to cutting resistance in case of using cast-iron lap, but the cutting resistance had proportional relations with only lapping quantity in case of using phenol-lap.
(4) Although lapping quantity, sphericity and surface condition depended on lapping liquid and lapping pressure in case of using cast-iron lap, and inclinations of lapping quantity and finished percentage were contrary to each other, these effects were small but stable in case of using phenol-lap. Therefore phenol-lap seems to excel in all points.

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In this paper, the experimental results and considerations are given on the mechanism of the formation of roughness, the effects of various machining conditions on the roughness and the methods for decreasing the surface roughness in the case of HCl solution, as compared with the NaOH solution reported in the preceding papers.
While the black smut which adhered to the machined surface was the main cause of the formation of roughness in the case of NaOH, the black smut was scarcely formed and the main cause of the roughness was the sparingly soluble impurities contained in the machined material in the case of HCl solution. The roughness by the former increased with the temperature and the concentration of the working solution, but the roughness by the latter tended to decrease with the temperature and the concentration.
The thin discolored layer, grey or dark-grey, was formed on the machined surface in the case of HCl solution. H owever, it could be eliminated by after-treatment with HF or NaOH solution. This after-treatment was also effective for the decrease of the roughness of machined surface.

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