Bit for drilling with casing or liner string and manufacture thereof

A method of drilling a wellbore, comprising:

• assembling a bit as part of a casing or liner string, the bit comprising:
• a tubular stem made from a high strength metal or alloy;
• a head:
• having a cutting face with an inner cone, an outer shoulder, and an intermediate nose between the cone and the shoulder;
• attached to an end of the stem;
• and
• made from a nonferrous metal or alloy;
• a plurality of blades formed integrally with the head, made from the nonferrous metal or alloy, and each extending from a center of the cutting face to the shoulder;
• a plurality of superhard cutters mounted along each blade;
• a plurality of gauge pads formed integrally with the stem;
• and
• a flush joint formed between each blade and a respective gauge pad,
• wherein:
• a yield strength of the high strength metal or alloy is at least twice a yield strength of the nonferrous metal or alloy,
• the end is a lower end of the stem,
• the bit further comprises a threaded coupling formed at an upper end of the stem for connection to the casing or liner string,
• the bit further comprises a lock joint and a lap joint attaching the head to the stem, and
• an outer portion of the head includes an essential portion of the lock joint;
• drilling the casing or liner string into the wellbore to extend the wellbore through a problem formation;
• cementing the casing or liner string into the wellbore;
• and
• drilling out an inner portion of the head with a polycrystalline diamond compact or roller cone second drill bit,
• wherein the outer portion of the head remains after drill-out.

A bit for drilling with a casing or liner string, comprising:

• a head having a cutting face with an inner cone and an intermediate nose and made from a nonferrous metal or alloy;
• a tubular stem attached to the head, having an outer shoulder of the cutting face, and made from a high strength metal or alloy;
• a plurality of first blades formed integrally with the head, made from the nonferrous metal or alloy, and each extending from a center of the cutting face to the nose;
• a plurality of superhard cutters mounted along each first blade;
• a plurality of second blades formed integrally with the stem, made from the high strength metal or alloy, and each having a curved shoulder portion and a gage portion;
• a plurality of superhard cutters mounted along each shoulder portion;
• and
• a flush joint formed between each first and second blade,
• wherein:
• a yield strength of the high strength metal or alloy is at least twice a yield strength of the nonferrous metal or alloy,
• the bit further comprises a lock joint and a lap joint attaching the head to the stem, and
• the lap joint has a lap coupling of the stem engaged with a lap coupling of the head.