Abstract: The present invention is a hydraulic control apparatus that activates and deactivates a downhole tool, such as a reamer, at a desired downhole location in a borehole. The apparatus includes a piston, a housing, a coil spring, and a guide pin. The piston has a cam portion with a continuous slotted groove. There is a slide member and a force member within the slotted groove so that the piston moves longitudinally and rotationally within the housing according to the guide pin within the slotted groove. At the desired downhole location, drilling fluid pressure passes a pressure threshold to move a front outlet of the piston to an opened position past an end of the housing, while rotating the piston according to the slide member and force member in the slotted groove. The apparatus alternately extends and retracts the reamer by opening and closing the front outlet by hydraulic control.