Tunneling machine and impact-tool cutting head therefor

Claim 1

A WORK HEAD FOR A TUNNELING MACHINE COMPRISING, A ROTATABLY MOUNTED TUBE-LIKE STEM HAVING AN ENLARGED HOLLOW FORWARD PORTION, SAID FORWARD PORTION HAVING A SUBSTANTIALLY CIRCULAR OPEN FRONT END AND OPENING REARWARDLY INTO SAID STEM, A PLURALITY OF IMPACT HAMMERS EACH HAVING A CUTTING TOOL RELEASABLY RETAINED THEREIN ARRANGED AROUND THE EXTERIOR OF SAID ENLARGED PORTION SUBSTANTIALLY PARALLEL WITH THE AXIS THEREOF, SAID CUTTING TOOLS PROJECTING BEYOND THE OPEN END OF SAID FORWARD PORTION AND EXTENDING RADIALLY WITH RESPECT TO THE CENTER THEREOF BEYOND THE MAXIMUM RADIAL DIMENSION OF SAID IMPACT HAMMERS, THE CENTERS OF SAID CUTTING TOOLS DEFINING A CIRCLE CONCENTRIC WITH SAID OPEN FRONT END, MEANS FOR RELEASABLY SECURING EACH OF SAID IMPACT HAMMERS TO SAID ENLARGED FORWARD PORTION, FRAME MEANS CARRYING AND SURROUNDING SAID STEM IMMEDIATELY BEHIND SAID ENLARGED FORWARD PORTION FOR ROTATABLY SUPPORTING SAID STEM AND ENLARGED FORWARD PORTION, MEANS FOR ROTATING SAID STEM IN SAID FRAME MEANS, A SHROUD SECURED TO SAID FORWARD PORTION FOR SURROUNDING SAID CUTTING TOOLS AND DIRECTING FLOW OF AIR ACROSS THE FACES OF SAID TOOLS WHEN SAID WORK HEAD IS IN OPERATING POSITION AND A SUCTION IS APPLIED TO SAID STEM, AND A CIRCULAR PLATE MOUNTED CONCENTRICALLY WITHIN THE OPEN END OF SAID ENLARGED FORWARD PORTION, SAID PLATE BEING OF A SIZE TO REDUCE THE OPEN AREA OF SAID FORWARD PORTION TO SUBSTANTIALLY THAT OF THE CROSS-SECTION OF SAID STEM.