Rotary cutting insert and tool having declined axial support surfaces

A cutting insert of a rotary drill tool for cutting metal comprising:

• a head and a neck extending along a longitudinal axis, the head having an axially forward facing cutting region and the neck having an axially rearward facing mount region, at least the neck being arranged to be rotationally, releasably mountable within a jaw of a support body, the head having axially rearward facing axial support surfaces projecting radially outward from the neck, for abutment with corresponding axial support surfaces of the support body, each of the support surfaces of the head including a first decline orientation aligned relative to a plane perpendicular to the longitudinal axis, such that a radially outer region of each said support surface of the head is axially rearward relative to a radially inner region of each said support surface of the head, each of said support surfaces of the head including a second decline orientation aligned to extend in a circumferential direction relative to the plane perpendicular to the longitudinal axis, wherein the second decline orientation extends such that a lead region or edge of each said support surface of the head in a rotational direction of the insert, is positioned axially rearward relative to a trailing region or edge of each said support surface in a rotational direction of the insert, and wherein the head of the insert is formed by a pair of diametrically opposed lobes each having a radially outermost envelope surface configured to align with corresponding radially outer envelope surfaces of the support body, and a substantially cylindrical locating surface defined between each of the opposed lobes:
• wherein the cutting insert has a total axial length A defined between a base structure and a cutting tip:
• the total axial length comprising a head axial length B defined between the cutting tip and a mid-length region extending between the trailing region or edge and the lead region or edge of each of the support surfaces, and a neck axial length C defined between the base surface and the mid-length region of each of the support surfaces, wherein a quotient of CB is in the range of 0.2 to 1.0;
• and
• two diametrically opposite first radial projections formed as ribs having a length extending in a circumferential direction and arranged to be seated within a channel of the support body to axially secure the insert to the support body, wherein each of the first radial projections is positioned in a circumferential direction between each of the lobes, and wherein each of the lobes include a radially and axially extending torque transfer surface for abutment contact with a corresponding torque transfer surface of the support body, wherein each of the radial projections extends from a cylindrical neck surface of the that is aligned at the same radial position as the cylindrical locating surface of the head, relative to the longitudinal axis.