Cutting tool with retainer having controlled hardness

Abstract

The present invention provides a rotatable cutting tool with a bit, a washer, and a retainer. The retainer surrounds at least a portion of the shank of the bit. Wear on the shank is reduced by providing a retainer with a controlled hardness that is less than the hardness of the shank of the bit, while still allowing similar wear on the retainer.

What is claimed is: 
     
         1 . A cutting tool comprising:
 a bit shank comprising a bit shank outer surface; and   a retainer comprising a retainer inner surface at least partially surrounding the bit shank outer surface,   wherein the retainer has a controlled hardness less than a hardness of the bit shank selected to reduce wear between the bit shank outer surface and the retainer inner surface.   
     
     
         2 . The cutting tool of  claim 1 , wherein the hardness of the bit shank outer surface is at least 2 HRC greater than the hardness of the retainer inner surface. 
     
     
         3 . The cutting tool of  claim 1 , wherein the hardness of the bit shank outer surface is at least 4 HRC greater than the hardness of the retainer inner surface. 
     
     
         4 . The cutting tool of  claim 1 , wherein the hardness of the bit shank outer surface is greater than 45 HRC, and the hardness of the retainer inner surface is less than 45 HRC. 
     
     
         5 . The cutting tool of  claim 1 , wherein the hardness of the retainer inner surface is at most 43 HRC. 
     
     
         6 . The cutting tool of  claim 1 , wherein the bit shank comprises 4140 type steel. 
     
     
         7 . The cutting tool of  claim 1 , wherein the retainer comprises 1070 grade spring steel or 65Mn steel. 
     
     
         8 . The cutting tool of  claim 1 , wherein the bit shank outer surface does not include a coating or hard facing. 
     
     
         9 . The cutting tool of  claim 1 , wherein the retainer inner surface does not include a coating or hard facing. 
     
     
         10 . The cutting tool of  claim 1 , wherein the retainer comprises a retainer radial thickness defined between the retainer inner surface and a retainer outer surface, the retainer radial thickness having a substantially constant retainer hardness throughout the retainer radial thickness in a radial direction. 
     
     
         11 . The cutting tool of  claim 1 , wherein the bit shank comprises a radial thickness defined by the bit shank outer diameter, the bit shank radial thickness having a substantially constant bit shank hardness throughout the bit shank radial thickness in a radial direction. 
     
     
         12 . A method of assembling a cutting tool, comprising installing a low hardness retainer around a cutting tool bit shank, wherein the low hardness retainer comprises an inner surface at least partially surrounding an outer surface of the bit shank, and the inner surface has a controlled hardness less than a hardness of the bit shank selected to reduce wear between the bit shank outer surface and the low hardness retainer inner surface. 
     
     
         13 . The method of  claim 12 , wherein the retainer comprises spring steel. 
     
     
         14 . The method of  claim 13 , wherein the spring steel comprises a 1070, 1050, 1060 or 65Mn grade spring steel. 
     
     
         15 . The method of  claim 12 , wherein the hardness of the bit shank outer surface is at least 2 HRC greater than the hardness of the retainer inner surface. 
     
     
         16 . The method of  claim 12 , wherein the hardness of the bit shank outer surface is at least 4 HRC greater than the hardness of the retainer inner surface. 
     
     
         17 . The method of  claim 12 , wherein the hardness of the bit shank outer surface is at least 45 HRC. 
     
     
         18 . The method of  claim 12 , wherein the hardness of the retainer inner surface is at most 43 HRC.