Rotatable bit having a resilient retainer sleeve with clearance

A rotatable bit assembly for use in an operation to engage a substrate wherein the rotatable bit is generally continuous engagement with the substrate, the assembly comprising:

• a holder having a bore;
• a rotatable bit including a rotatable bit body having an axial forward end and an axial rearward end, the rotatable bit body further including a reduced diameter portion adjacent to the axial rearward end thereof defining a reduced diameter surface;
• a hard insert affixed to the rotatable bit body at the axial forward end thereof;
• a resilient retainer sleeve having a thickness and presenting an interior surface, and the retainer sleeve being carried by the rotatable bit body within the reduced diameter portion;
• the resilient retainer sleeve being in an expanded condition when the rotatable bit is not within the bore of the holder and the resilient retainer sleeve being in a compressed condition when the rotatable bit being within the bore of the holder;
• and
• the clearance between the reduced diameter surface of the rotatable bit body and the interior surface of the resilient retainer sleeve when the resilient retainer sleeve is in its compressed condition being at least as great as the thickness of the resilient retainer sleeve.

A resilient retainer sleeve for use on a rotatable drilling bit retained in a bore of a holder wherein the drilling bit body has an axial forward end and an axial rearward end with a shank adjacent the axial rearward end, the drilling bit body further includes a reduced diameter portion in the shank defining a reduced diameter surface, the resilient retainer sleeve comprising:

• a retainer sleeve body having a thickness and presenting an interior surface, and the retainer sleeve body being carried by the drilling bit body within the reduced diameter portion;
• the retainer sleeve body being in an expanded condition when the drilling bit is not within the bore of the holder and the retainer sleeve body being in a compressed condition when the drilling bit being within the bore of the holder;
• and
• the clearance between the reduced diameter surface of the drilling bit body and the interior surface of the retainer sleeve body when the retainer sleeve body is in its compressed condition being at least as great as the thickness of the retainer sleeve body.

An auger drill for engaging a substrate, the auger drill comprising:

• a central auger shaft;
• a helical flight on the auger shaft, and the helical flight having a leading edge;
• at least one drilling bit connected to the helical flight adjacent the leading edge wherein the drilling bit is retained in a bore of a holder;
• the drilling bit comprising:
• a drilling bit body having an axial forward end and an axial rearward end, the drilling bit body further including a reduced diameter portion adjacent to the axial rearward end thereof defining a reduced diameter surface;
• a hard insert affixed to the drilling bit body at the axial forward end thereof;
• a resilient retainer sleeve having a thickness and presenting an interior surface, and the retainer sleeve being carried by the drilling bit body within the reduced diameter portion;
• the resilient retainer sleeve being in an expanded condition when the drilling bit is not within the bore of the holder and the resilient retainer sleeve being in a compressed condition when the drilling bit being within the bore of the holder;
• and
• the clearance between the reduced diameter surface of the drilling bit body and the interior surface of the resilient retainer sleeve when the resilient retainer sleeve is in its compressed condition being at least as great as the thickness of the resilient retainer sleeve.

A drilling bit for use in conjunction with a holder having a bore, the drilling bit comprising:

• a drilling bit body having an axial forward end and an axial rearward end, the drilling bit body further including a adjacent to the axial rearward end thereof, and the shank containing a reduced diameter portion that defines a reduced diameter surface, the reduced diameter portion having a diameter;
• a hard insert affixed to the drilling bit body at the axial forward end thereof;
• a resilient retainer sleeve having a thickness and presenting an interior surface, and the retainer sleeve being carried by the drilling bit body within the reduced diameter portion;
• and
• the ratio of the thickness of the resilient retainer sleeve to the diameter of the reduced diameter portion ranges between about 0.08 and about 0.12.

A drilling bit comprising:

• a drilling bit body having an axial forward end and an axial rearward end;
• the drilling bit body further including a reduced diameter portion adjacent to the axial rearward end thereof, the reduced diameter portion having a groove diameter and having a groove surface;
• and a larger diameter shank portion axial forward of the reduced diameter portion, the larger diameter shank portion having a shank diameter and having a shank surface;
• a hard insert affixed to the drilling bit body at the axial forward end thereof;
• a resilient retainer sleeve being carried by the drilling bit body within the reduced diameter portion;
• and
• the resilient retainer sleeve having a thickness that is less than or equal to one-half of the dimensional difference between the shank surface and the groove surface.

A drilling bit comprising:

• a drilling bit body having an axial forward end and an axial rearward end;
• the drilling bit body further including a reduced diameter portion adjacent to the axial rearward end thereof, the reduced diameter portion having a groove diameter;
• and a larger diameter shank portion axial forward of the reduced diameter portion, the larger diameter shank portion having a shank diameter;
• a hard insert affixed to the drilling bit body at the axial forward end thereof;
• a resilient retainer sleeve being carried by the drilling bit body within the reduced diameter portion, the resilient retainer sleeve having an exterior surface that is generally smooth;
• and
• the ratio of the groove diameter to the shank diameter ranges between about 0.69 and about 0.80.