{HEAD ~ means} for selectively raising and lowering said work surface to a predetermined distance from {TAIL ~ said reflector} when said laser beam is broken 
{ HEAD ~ means } for selectively raising and lowering said work surface to a predetermined distance from { TAIL ~ said reflector } when said laser beam is broken
HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH