All of the major factors of surface roughness can be attributed to one or combinations of four elements, such as (1) feed marks, (2) worn cutting edge, (3) built-up-edge, (4) rigidity of machine tools. The feed marks are the result of feed and tool nose radius combining to form the gross variations in a generated surface. They say that in the case of rather large feeds the experimental relationship H_m=f²/8R agrees with actual surface roughness, where H_m, f and R are the maximum height of machined surface, feed and nose radius respectively However the relationship does not necessarily hold in a wide combination of feeds and nose radius. In fact, according to the tests, it was proved to be rather inconsistent or unreasonable in some cases.
With regard to the worn cutting edge, it affects the roughness considerably in the case of form cutting. Assuming that the cutting edge is free from built-up-edge, the irregularities on the machined surface are the printed patterns of the cutting edge.
The third factor, built-up-edge is the most serious, because more or less it is found almost on every machined surface and it is not so easy to control practically.
Rigidity of machine tools is also an important factor through chatter marks, but it is the problem of machine or tool system, so that it is not treated with in this report. This report treats with mainly the two factors of feed marks, and built-up-edge. Concerning the feedmarks, theoretical formulas of the average surface roughness H_avg were derived through geometrical computations of feeds, nose radius, end cutting edge angles and side cutting edge angles. According to the comparison between the theoretical formulas and the experimental results, they hold very well in the case of the metals free from built-up-edge, but a considerable deviation could be found for such metals as steels producing heavy built-up-edge. The next step was to examine the speed effect upon built-up-edge or surface roughness which is considered to be the most effective to suppress built-up-edge.

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A new surface-roughness tester which is the application of the compact electromagnetic micrometer designed by the author has a tracing needle which moves on the surface and records acurrately the surface profile. So this tester is applicable to the machine parts of large scale. Moreover, since the electric magnification makes its mechanism simple and sturdy and be of high reliability, the apparatus can be easily used in machine shops.

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The states of lapped surfaces have been examined by means of electron microscope and electron diffraction method, and the results are as follows :
(1) In wet lapping by coarse abrasives (c. f. WA or GC), the action of lapping consists in minute scratching by the pointed edges of abrasives at the initial stage as had been reported in the third report. When the lapped work is passed at the same position of the lap without charging of abrasives, the pointed edges are worn out, and the action of lapping changes into scratching by rounded edges of abrasives as shown in Figure 1.
(2) In the dry lapping, the lapping process is flow of the surface layer as Figure 2, but with a very smooth surface the surface flow can not be recognized.
(3) The embedding of abrassives under the surface of copper is found by the electron micrograph shown in Figure 3 with the aid of the thin sectioning. This is hard to be detected by electron diffraction under the surface of quenched steel.
(4) Chips produced by dry lapping contain αFe and γFe₂O₃ as shown in the electron diffraction pattern (Figure 4). It is considered that the surface is covered with amorphous or fine crystalline γ·Fe₂O₃ according to this pattern and the fact that the electrical resistance of the surface is very high.

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The shearing energy of the impact shearing of rolled Pb-brass was measured by simple testing equipment, and the shape of sheared section was examined. The shearing work and sheared section changes according to the Pb percentage and reduction of plate just as in the case of the static test, but the effect of Pb to the shearing work in this case is slightly larger compared with in latter case. On supported shearing, the highly reduced plate containing Pb more than about 1% requires much energy for banishing. When shearing cracks from edges of die and punch are not easily connected, secondary cracks along the rolled layer grow and complete the shearing. Secondary cracks are apt to grow under the following conditions : 1) more than 1% Pb, 2) high reduction, 3) large clearance, 4) shearing plane in accordance with the direction of rolling.

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