Survival kit for overseas living

A machine tool control system moves a grinding wheel from a retracted position to a forward position by applying hydraulic fluid to a hydraulic cylinder to effect a rapid forward movement of the grinding wheel whereupon further movement of the grinding wheel to a final position is effected by supplying a predetermined number of pulses to a stepping motor for driving a feed screw in accordance with a predetermined sequence of grinding movements. The actual advancement of the grinding wheel is monitored by an absolute multiturn encoder rotatably associated with the feed screw and producing a signal which is compared to a combined signal representative of the desired size of the workpiece in the range of grinding. With each grinding sequence, the portion of the feed range signal is reduced to create a difference from a signal produced by the encoder so as to operate a sequence controller to effect advancement of the grinding wheel by supplying pulses to a stepping motor drive circuit connected to controlling relation with a stepping motor connected to a feed screw through a gear train. When the workpiece is ground to the desired size, the sequence controller operates to reversely rotate the stepping motor and reverse the application of hydraulic fluid to return the grinding wheel to a retracted position. The desired size of the workpiece and the advancement of the grinding wheel under the control of the encoder are displayed by suitable gauges on a display panel. The mechanical relation of the encoder to the grinding wheel may be calibrated by a calibration offset signal for increasing or decreasing the signal produced by the encoder indicating the position of the grinding wheel. To enable the actual position of the grinding wheel to be varied without disturbing the relationship between the encoder and the stepping motor in associated circuitry, the feed screw is driven through a gear train including a differential. The encoder is associated with the input gear of the differential while a compensating motor and associated circuitry are provided for rotating the output gear of the differential without effecting the rotational movement of the encoder.