Cutting element assemblies comprising rotatable cutting elements, downhole tools comprising such cutting element assemblies, and related methods

Abstract

Rotatable cutting element assemblies includes a sleeve, a centering element positioned at least partially within the sleeve, a biasing element configured to apply a force against the centering element, and a rotatable cutting element coupled to the centering element and configured to rotate relative to the sleeve. Earth-boring tools include a tool body and at least one rotatable cutting element assembly coupled to the tool body. The at least one rotatable cutting element assembly includes a sleeve fixedly coupled to the tool body, a centering element positioned at least partially within the sleeve, a rotatable cutting element coupled to the centering element, and a biasing element configured to apply a force against the centering element. Methods of forming an earth-boring tool include positioning a centering element within a sleeve, fixedly coupling the sleeve to a tool body, and coupling a rotatable cutting element to the centering element.

What is claimed is: 
     
         1 . A rotatable cutting element assembly for an earth-boring tool, comprising:
 a sleeve comprising a sidewall and a protrusion extending inward from the sidewall;   a centering element positioned at least partially within the sleeve and configured to abut against the protrusion;   a biasing element configured to apply a force against the centering element toward the protrusion; and   a rotatable cutting element coupled to the centering element and configured to rotate relative to the sleeve.   
     
     
         2 . The rotatable cutting element assembly of  claim 1 , wherein:
 the centering element comprises a bore extending at least partially through the centering element; and   the rotatable cutting element comprises a hole extending at least partially through the rotatable cutting element along a central axis of the rotatable cutting element.   
     
     
         3 . The rotatable cutting element assembly of  claim 2 , further comprising a fastener coupling the rotatable cutting element to the centering element using the bore and the hole. 
     
     
         4 . The rotatable cutting element assembly of  claim 2 , wherein the bore extends fully through the centering element and the hole extends fully through the rotatable cutting element. 
     
     
         5 . The rotatable cutting element assembly of  claim 2 , wherein the hole in the rotatable cutting element is a stepped through-hole comprising a first portion that is wider than a second portion, a lip defined at a transition from the first portion to the second portion. 
     
     
         6 . The rotatable cutting element assembly of  claim 1 , wherein:
 a portion of the centering element protrudes from the sleeve past the protrusion of the sleeve; and   the rotatable cutting element comprises a centering surface complementary to an exterior surface of the protruding portion of the centering element.   
     
     
         7 . The rotatable cutting element assembly of  claim 1 , wherein, absent external forces, a gap is defined between a bottom surface of the rotatable cutting element and a top surface of the sleeve. 
     
     
         8 . The rotatable cutting element assembly of  claim 1 , wherein the rotatable cutting element is configured to rotate about its central axis relative to the sleeve. 
     
     
         9 . The rotatable cutting element assembly of  claim 1 , wherein the sleeve comprises a base, further comprising a fastener threaded to the base and extending through at least a portion of the rotatable cutting element and the centering element. 
     
     
         10 . The rotatable cutting element assembly of  claim 1 , further comprising a centering element support positioned between the centering element and the biasing element. 
     
     
         11 . An earth-boring tool, comprising:
 a tool body; and   at least one rotatable cutting element assembly coupled to the tool body, the at least one rotatable cutting element assembly comprising:
 a sleeve fixedly coupled to the tool body; 
 a centering element positioned at least partially within the sleeve; 
 a rotatable cutting element coupled to the centering element and configured to rotate relative to the tool body; and 
 a biasing element configured to apply a force against the centering element. 
   
     
     
         12 . The earth-boring tool of  claim 11 , wherein the sleeve comprises a sidewall and a protrusion extending inward from the sidewall, the protrusion sized and shaped to maintain the centering element at least partially within the sleeve. 
     
     
         13 . The earth-boring tool of  claim 11 , wherein the sleeve is brazed to the tool body. 
     
     
         14 . The earth-boring tool of  claim 11 , wherein the tool body comprises a fixed blade, and the sleeve is positioned within a pocket in the fixed blade. 
     
     
         15 . The earth-boring tool of  claim 11 , further comprising a fastener coupling the rotatable cutting element to the centering element. 
     
     
         16 . The earth-boring tool of  claim 15 , wherein the fastener extends into a hole formed in the tool body. 
     
     
         17 . A method of forming an earth-boring tool, the method comprising:
 positioning a centering element within a sleeve;   positioning a biasing element within the sleeve and adjacent to the centering element;   fixedly coupling the sleeve to a tool body within a pocket of the tool body; and   coupling a rotatable cutting element to the centering element, the rotatable cutting element rotatable relative to the tool body.   
     
     
         18 . The method of  claim 17 , further comprising attaching a base of the sleeve to a sidewall of the sleeve after positioning the centering element and the biasing element within the sleeve to maintain the centering element and the biasing element within the sleeve. 
     
     
         19 . The method of  claim 17 , wherein coupling the rotatable cutting element to the centering element comprises attaching the rotatable cutting element to a ball with a fastener. 
     
     
         20 . The method of  claim 19 , wherein the rotatable cutting element is rotatable about its central axis relative to the fastener and relative to the tool body.