A heavy-duty live center for lathes, grinders and like machine tools in which the work load is in excess of ten tons and includes visual means for indicating the thrust on the live center, said center including:
- (a) a hollow quill;
- (b) a rotatable spindle carried in this quill, the quill in mounted condition having a work load supporting and extending beyond the quill and with the intermediate portion of the spindle sized so as to provide sufficient clearance between the bore and spindle for the spindle to bow with the application of a heavy load and when bowed the spindle turns freely in the quill;
- (c) a self-aligning roller bearing mounted on the foreportion of the spindle and adjacent thereto and to the rear thereof is a self-aligning spherical roller thrust bearing;
- (d) a front bore formed in this quill, the front portion of this bore precisely sized to receive and retain the outer race of the self-aligning roller bearing and the rear portion of this front bore is made a determined amount oversized in its diameter with regard to the diameter of the outer race of the thrust bearing, the rear of this front bore having a face surface normal to the axis of the bore, this face surface providing a stop surface for the rear face of the outer race of the thrust bearing, this thrust on the bearing being transferred to this face and thence to the quill;
- (e) antifriction bearing means mounted on the rear of the rotating spindle and when mounted in the bore of the quill adapted to receive and support the rear of the spindle;
- (f) a biasing means in association with the spindle and said bearing means on the rear of the spindle and adapted to provide a preload to the bearings carried in the front bore of the quill;
- (g) a shoulder provided on the fore-portion of the spindle, this shoulder adapted to engage the inner race of the self-aligning bearing and as urged by the applied preload to this spindle the bearing is drawn rearwardly and as this bearing is moved rearwardly its inner race moves the inner race of the self-aligning spherical roller thrust bearing rearwardly to cause the outer race of said thrust bearing to be brought into sliding engagement with the inner rear face surface of the front bore;
- (h) sealing means in association with the spindle and front bore of the quill to close the front bore to dirt, coolant and the like to retain a lubricant in the bearings without contamination and when a heavy load is placed on the extending end of the spindle, the spindle is bowed in accordance with the load and the stiffness of the spindle, the self-aligning bearing moving into alignment with the bowing of the spindle and the outer race of the thrust bearing is moved in the enlarged bore an amount equal to the bowing of the spindle at the inner race of the thrust bearing;
- (i) a hydraulic load cell carried by and in the rear portion of the quill and including a recess ring portion and a piston portion carried by and in this recess in a fluid tight manner, one member portion carried in a fixed condition by and in the quill and the other movable member slidably carried by the fixed member;
- (j) a nut-like member slidably carried in the quill and adapted to mate with and engage a threaded screw as carried by a tailstock of the machine tool;
- (k) a heavy-duty spring-like overtravel member carried by the nut-like member and interposed between this spring and the slidable mating member of the hydraulic load cell, and (1) a hydraulic conductor leading from the hydraulic load cell to and connected to a hydraulic gage secured to the quill, the hydraulic gage indicating the pressure in the load cell as the work load is mounted and expands under working conditions, the spring-like overtravel member providing the needed bias to limit the movement of the quill under the increased thrust to a determined limit of travel.