The crusher replaces the drilling machine upon completion of the drilling of {HEAD ~ a guide hole} by {TAIL ~ the drilling machine} 
The crusher replaces the drilling machine upon completion of the drilling of { HEAD ~ a guide hole } by { TAIL ~ the drilling machine }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL