"PDC bit" and "rock bit" are essentially the same thing. The term "rock bit" is a more generic and colloquial way of referring to a drill bit used for drilling through rock formations, while "PDC bit" specifically refers to a type of rock bit that uses PDC (Polycrystalline Diamond Compact) cutters.
PDC bits, as mentioned earlier, have a cutting structure that consists of fixed PDC cutters. These cutters are made by combining diamond grit and a metal binder using high temperature and pressure. The resulting PDC cutters are extremely hard and wear-resistant, making them highly effective for drilling through various rock formations.
The term "rock bit" can encompass a broader range of drill bits used for drilling in rock formations, including tricone bits, which are another common type of rock bit. Tricone bits, as explained in the previous response, have three rotating cones with teeth or inserts that crush or gouge the rock as the bit rotates.
In summary, the main difference between a PDC bit and a rock bit is that a PDC bit specifically refers to a type of rock bit that utilizes PDC cutters, while "rock bit" is a more general term that can include various types of drill bits used for drilling in rock formations, including PDC bits and tricone bits.