An adjusting mechanism for a cutting tool having knife holders circumferentially interspaced and having a back surface facing a circumferential direction and a seat surface facing a radial direction. The mechanism includes a support member having fixation points securable to the cutting tool. A deformable member is sandwiched between the cutting tool and the support member. The deformable member defines an adjustable lateral reference surface facing an axial direction to be in abutment with the knife inserts. An adjustment member is mounted on one of the support member and the deformable member between the fixation points of the support member. The adjustment member is operable to exert a force on the deformable member to locally deform the deformable member from an undeformed state to a deformed state. An axial distance between the support member and the deformable member is greater in the deformed state than in the undeformed state.