Notwithstanding the grade (or hardness) of grinding wheels is the most important factor in grinding practice and the production of wheels, there are many uncertain matters in measuring methods and the standard value of grade.
Grade implies bonding strength and the combined breaking strength of grain and bond. This report describes the relationship between these two kinds of strength, and measuring method.

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In order to determine the flank profile and the half-angle of the thread, a new screw thread flank tester, which consists of bed, sine-table, column, carriage, electronic micrometer and pen-recorder, is developed.
The measuring method is as follows. A screw thread to be examined is made as to be inclined by the nominal half-angle of the thread by means of the sine-table, and then the generator of the upper flank lies parallel to the direction of the carriage displacement. The deviation of the flank from the ideal profile is detected by the moving stylus in the vertical plane containing the line of the greatest slope of the sine-table, and recorded on a strip of chart paper the movement of which is synchronized with the stylus displacement.
The measuring error of the half-angle of the thread due to the fact that the line of the direction of the stylus displacement does not literally intersect the center line of the gauge is estimated. The measuring accuracy of the profile being able to be kept within ± 0.3μ, the half-angle of the thread can be measured with an accuracy within ±2.0 in the case of the API standard screw threaded gauges of the diameter 50 to 600 mm.

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Up to this time, surface roughness as a factor of measuring error has been left out of consideration. But in accurate measurement, careful consideration must be given to the surface roughness of the specimen.
In order to make clear the relation between surface roughness and the accuracy of measurement, an apparatus has been prepared by which real measuring force of micrometers can be obtained when the diameter of cylindrical specimens are measured.
The experiments are carried out by measuring the diameters of ground specimens made of four kinds of materials under different measuring forces. And the results are summarized as follows :
The diameter decreases as the measuring force increases and the decreasing ratio of the diameter to measuring force relates to both surface roughness and Brinel hardness of the test piece, and further measured values present hysteresis as the measuring force increases and decreases.
These facts mean that the peaks of the surface is yielded by the feeler.
A method is suggested, by which a reasonable diameter of a test piece can be induced. For this purpose it is convenient to introduce "profile factor" which is a ratio of the maximum height of surface roughness compressed by length measurement to the maximum height of its virgin surface.
When the profile factor is obtained, reasonable length of the object can be known when measuring force and material of the test piece are given.

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In this report accuracy of length measurement relating to the mechanical contact between spherical surface of feeler and the test piece is discussed.
In order to make clear these relations, displacement of a lapped disc tracing on the specimen is recorded by a roughness meter. And one more factor "reducing factor" is added to the profile factor suggested in the previous paper. The reducing factor means a ratio of the maximum height of the recorded envelope curve to the maximum height of the surface roughness. Introducing the reducing factor, reasonable length and distribution of the measured values can be known when measuring force and radius of curvature of the feeler and material of the test specimen are given.
And further the authors suggest that the radius of curvature of the spherical surface of skid used for recording envelope curve of the surface is more than about four thousands times the maximum height of surface roughness.

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The purpose of this report is to offer the fundamental knowledge of tool wear or tool ife, and accordingly to find out the method to predict the tool life without performing the conventional tool life test.
The important findings are as follows.
(1) The tool life or wear in continuous cutting can be analysed into the mechanics of rate process and that of mechanical abrasion, the former being wholly dependent upon the cutting temperature.
(2) Under practical conditions with sintered carbide tools, the rate of tool wear or the tool life is determined mostly by the initial cutting temperature and independent of the other cutting conditions.

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