Rock bit dullness indicator

Claim 1

IN ROTARY DRILLING APPARATUS EMPLOYING A DRILL STRING THROUGH WHICH DRILLING FLUID IS CIRCUATED DURING DRILLING OPERATIONS, THE IMPROVEMENT COMPRISING: MEANS ATTACHABLE TO THE LOWER END OF SAID DRILL STRING HAVING MEANS CONTAINING CUTTER TEETH ROTATIVELY MOUNTED THEREON; A FIRST CHAMBER FORMED IN SAID MEANS ATTACHABLE TO THE LOWER END OF SAID DRILL STRING CAPABLE OF FLUIDLY COMMUNICATING THE INTERIOR AND EXTERIOR OF SAID DRILL STRING; AN INDICATOR PLUG REMOVABLY ARRANGED IN SAID FIRST CHAMBER; A SECOND CHAMBER FORMED IN SAID MEANS ATTACHABLE TO THE LOWER END OF SAID DRILL STRING INTERSECTING SAID FIRST CHAMBER AND CONTAINING PROBE MEANS AND LOWER END OF WHICH ENGAGES SAID CUTTER TEETH; AND MEANS RELEASABLY COUPLING SAID INDICATOR PLUG AND SAID PROBE MEANS ADAPTED TO RELEASE SAID INDICATOR PLUG TO PERMIT REMOVAL OF SAID INDICATOR PLUG BY DRILLING FLUID CIRCULATING PRESSURE UPON DOWNWARD MOVEMENT OF SAID PROBE MEANS IN RESPONSE TO WEAR OF SAID CUTTER TEETH WHEREBY AN INDICATION OF REMOVAL OF SAID INDICATOR PLUG IS PROVIDED AT THE SURFACE BY A DROP IN DRILLING FLUID CIRCULATING PRESSURE.