There are three basic types of PDC bit crown profile: flat or shallow cone; tapered or double cone; and parabolic. There are variations on these themes but most bits can be classified into these categories.
The flat or shallow cone profile evenly distributes the WOB among each of the cutters on the bit (Figure 21). Two disadvantages of this profile are limited rotational stability and uneven wear. Rocking can occur at high RPM, because of the flat profile. This can cause high instantaneous loading, high temperatures and loss of cooling to the PDC cutters.
The taper or double cone profile (Figure 22) allows increased distribution of the cutters toward the O.D. of the bit and therefore greater rotational and directional stability and even wear is achieved.
The parabolic profile (Figure 23) provides a smooth loading over the bit profile and the largest surface contact area. This bit profile therefore provides even greater rotational and directional stability and even wear. This profile is typically used for motor or turbine drilling.