Patent ID: 7207402

Claim:
A percussion drill bit for drilling a bore, comprising: a rotary drill body including a rear connection section and a front head section; and a plurality of regrindable cemented carbide buttons carried by the drill body, each button defining a longitudinal center axis and comprising: a rear mounting portion embedded in the front head section and defining a largest diameter, and a front cutting portion protruding from the drill body by a distance no less than 50% of the largest diameter of the rear mounting portion, the front cutting portion having an outer surface extending forwardly from a junction with an envelope surface of the mounting portion, the outer surface including: a front surface portion of substantially semi-spherical shape having a radius whose origin lies on the longitudinal center axis at a location rearwardly of the junction, and a conical surface portion extending between the junction and the front surface portion and increasing in cross section as it approaches the junction, the conical portion forming an acute angle in the range of about 13–19 degrees with the envelope surface of the mounting portion.