Abstract: A frame-like nozzle for liquid coolant disposed above a machining tool is connected to a vertical main shaft. The nozzle is coaxial with the main shaft and directed downward. The nozzle has an inner peripheral wall, an inner flange formed in or close to the inner peripheral wall, an upper framework having a ceiling serving as a guide surface, and a lower framework. The liquid coolant flows upwardly out from the inside channel in a planar radial manner. The upper framework has an outer peripheral wall serving as an outside guide surface for downwardly bending the liquid and cooperating with the flange to define an outside channel. A flow agitating recess is formed in the wall surface. The lower framework includes a level difference, and forms a floor by which the coolant reaching the lower end of the outer peripheral wall is guided radially inward through the difference. Coolant is allowed to flow downward. The inner edge of the floor defines a circulatory waterfall opening.

Abstract: A coolant liquid feeding method comprises feeding a coolant liquid, with air bubbles caused to form continuously therein, for cutting or grinding operation to a region under machining, expediting the splashing of air bubbles in all directions when the air bubbles impinge on the region under machining and burst, and also expediting the entry of accelerated splashed liquid particles into a cutter/workpiece pressure contact plane, thereby improving the cooling and lubrication of the region under machining, whereby the air bubbles in the coolant liquid which has failed to reach the region under machining or which, though reaching there, has left there for the recovery channel are allowed to adhere to suspended foreign matters in the liquid, thereby expediting the surfacing of the foreign matters.