Limits and tolerances are the basis of all machine manufacture. Fourteen European countries adopted the system known as the ISA (International Federation of National Standards Associations) in December 1936; the system covers all grades of finish from the finest roller bearings to rough agricultural machines. Certain fixed principles of measurement must be observed, both in the manufacture of new machines and in the repair of old ones; for instance, extremely fine boring and grinding machines and jig borers are now obtainable and can be used equally for the manufacture of a new motor car or for the overhauling of an old one. Before a satisfactory basis for the establishment of correct limits for the manufacture of, say, drilling machines, lathes, and milling machines, the deformations set up during the cutting operations must be known. These deformations must therefore be measured during actual cutting. The measuring apparatus as applied to lathes, drilling machines, and milling machines, though varying greatly in individual cases, can be adapted to this research, which furnishes information on the admissible variations in deformation—which is of use during inspection—and on the forces and bending and twisting moments—which is of use to the designer. These records furnish manufacturers with the information required for organizing the sequence of operations when building machines to work with any desired precision. The “balance sheets” of various machines, giving the relationships of the forces, speeds, feeds, section of chip, power required, and efficiency, are of great value both to manufacturer and user.
Intermittent heat instabilities in an air plume