In lapping steel balls, it is an important point that lapping efficiency and finished surface are affected by contact state of grits which lie between steel ball and lap. The cutting mechanism is very different from common flat lapping, and it seems that grinding action is the main part of the performance of grits, just as in ultrasonic machining.
We can expect that lapping pressure has influence not only on lapping efficiency, but also on sphericity of steel ball. In this report, accordingly, we, describing the result of theoretical analysis on the various cases of contact due to the lapping pressure, consider the effect of each lapping condition.
Namely, we calculated the lapping pressure exceeding the limit pressure and the change of contact limit pressure influenced by grit diameter and surface roughness from its contact state when the radius of steel ball is about I mm. Then we found out that the metallic contact occurs correspondingly to the grit diameter and the sum of the mean roughness which is changeable according to supplying method of lapping compound under the same lapping pressure.

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The radius of curvature of Rockwell diamond indenter is one of the most important factors for the accurate estimation of hardness, but an adequate method has not been discovered. A new apparatus was designed applying the method of microscopic collimation. The principle of this method is shown in Fig. I in which O₁ is the image of pin hole S₁, M is a half silvered mirror, objective O₁, and eyepiece E construct an ordinary microscope, O₁, and O₂ are centers of a sphere with radius r and the distance of O₁, O₂ is r. When S₁ and S₂ are at symmetrical position with respect to M the image of S₁ is formed at S₂ in the two positions of sphere of O₁ and O₂ being reflected by the surface of the sphere. In this condition sharp image of S₁ can be observed in the field of microscope.
The measuring error of this apparatus is due to symmetry of S₁ and S₂ and depth of distinct vision of microscope. Concerning these factors analysis and experiments were carried out and the following results were obtained : In order to keep the measuring accuracy within I micron, the defference of CS₁ and CS₂ must be less than 5.6 mm when the magnification of objective is × 40.
The measuring accuracy concerning depth of distinct vision is illustrated in Table 2 for some combinations of objectives and eyepieces in which we can see the error is less than 0.4 micron for the combination of objective × 40 and eyepiece × 10.

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In the foregoing paper, the machining performance, the tool wear process, the economical machining conditions, etc., when machining Meehanite cast iron, with a home made ceramic tool were studied. The conclusion was that the ceramic tool can be successfully applied for machining cast iron from a practical point of view.
Here in this paper, the same items have been analysed when machining an alloy steel, while being compared with a carbide tool of a steel-cutting grade. The conclusion is that the home made ceramic tool is not reliable enough to be applied for machining steels. The reason for this seems to lie in its inconsistency due to chipping or brittleness of the cutltng edge.

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