Tool for dressing the surface of a conical hole

Claim 1

A ROTARY TOOL FOR DRESSING THE SURFACE OF A CONICAL HOLE IN A VITREOUS WORK-PIECE COMPRISING A BODY PORTION OF CIRCULAR CROSS-SECTION, SAID BODY PORTION BEING CONICAL WITH THE PAPER TOWARDS ITS OPERATIVE END, THE TAPER BEING AT THE SAME ANGLE AS THE FINAL CONICAL HOLE IN THE WORKPIECE IS TO HAVE, AN ABRADANT LAND OF DIAMOND DUST INTEGRAL WITH SAID BODY, SAID ABRADANT LAND BEING IN THE FORM OF A SPIRAL HELIX THE WINDING OF WHICH IS IN THE DIRECTION SO THAT WHEN SAID TOOL IS ROTATED, THE HELIX WILL BE ROTATED IN ITS UNSCREWING DIRECTION SO THAT BINDING OF THE TOOL IN THE WORK-PIECE IS AVOIDED AND A FLOW OF THE GROUND PARTICLES AWAY FROM THE CUTTING ZONE IS PROMOTED, SAID TOOL HAVING A LONGITUDINAL BORE, SAID BORE CLOSED AT THE OPERATIVE END OF THE TOOL AND ADAPTED AT ITS OTHER END TO RECEIVE A SUPPLY OF A COOLANT, AND SAID TOOL PROVIDED WITH A DUCT LEADING FROM SAID BORE TO A PART OF THE OUTER CONICAL SURFACE OF SAID TOOL CIRCUMFERENTIALLY SPACED FROM SAID LAND FOR CONVEYING THE COOLANT TO THE CUTTING ZONE.