a control circuit for a honing machine such that the honing head can be driven and the machine manually operated by an operator or , alternatively , the unit can be placed in the auto stroke mode such that a pair of limit switches control the up and down honing operation of the system . the limit switches actuate a number of solenoid valves which cause the honing head to be moved up and down in a cylinder automatically . by setting the position of a pair of trip discs , the travel limits can be set for the system .