Bearings for downhole tools, downhole tools incorporating such bearings, and related methods

1. A bearing system configured for use on a downhole tool including a rolling cutter member, the rolling cutter member including a plurality of cutting structures, comprising:

a head washer;

an at least substantially planar shaft washer;

a first plurality of bearings disposed between the head washer and the at least substantially planar shaft washer;

a rolling cutter washer; and

a second plurality of bearings disposed between the at least substantially planar shaft washer and the rolling cutter washer;

wherein the at least substantially planar shaft washer is directly interposed between, and in contact with, the first plurality of bearings and the second plurality of bearings.

2. The bearing system of claim 1 , wherein at least one of the first plurality of bearings and the second plurality of bearings comprises rolling bearing elements.

3. The bearing system of claim 2 , wherein the rolling bearing elements comprise tapered rolling bearing elements.

4. The bearing system of claim 2 , wherein the rolling bearing elements comprise cylindrical rolling bearing elements.

5. The bearing system of claim 1 , wherein at least one of the first plurality of bearings and the second plurality of bearings comprises opposing sets of non-rolling bearing elements each including a volume of polycrystalline diamond material, the polycrystalline diamond material of a first set of the opposing sets configured to abut against and slide relative to the polycrystalline diamond material of a set of the opposing sets during operation of the bearing system.

6. The bearing system of claim 1 , wherein the head washer is integrally formed with, and comprises an integral portion of a head.

7. An earth-boring tool configured for use in a subterranean formation, comprising at least the following components:

a tool body including at least one head; and

a rolling cutter mounted on the at least one head; and

a bearing system disposed between the at least one head and the rolling cutter mounted on the at least one head, the bearing system including:

a head washer disposed on the at least one head;

an at least substantially planar shaft washer retained within the rolling cutter and disposed around the at least one head;

a first plurality of bearings disposed between the head washer and the at least substantially planar shaft washer;

a rolling cutter washer retained within the rolling cutter; and

a second plurality of bearings disposed between the at least substantially planar shaft washer and the rolling cutter washer;

wherein the at least substantially planar shaft washer is directly interposed between, and in contact with, the first plurality of bearings and the second plurality of bearings.

8. The earth-boring tool of claim 7 , wherein the bearing system comprises a thrust bearing system, and wherein at least one of the components of the thrust bearing system is capable of sliding in a radial direction relative to at least one other of the components of the thrust bearing system so as to provide a selected degree of radial play between the rolling cutter and the at least one head.

9. The earth-boring tool of claim 7 , wherein the earth-boring tool comprises a rolling cutter earth-boring rotary drill bit.

10. The earth-boring tool of claim 7 , wherein the earth-boring tool comprises an earth-boring rotary hybrid drill bit.

11. The earth-boring tool of claim 7 , wherein the earth-boring tool comprises a reamer configured to enlarge a diameter of a previously drilled wellbore.

12. The earth-boring tool of claim 7 , wherein the at least substantially planar shaft washer is configured to slide in the radial direction relative to the first plurality of bearings and the second plurality of bearings.

13. The earth-boring tool of claim 7 , wherein at least one of the first plurality of bearings and the second plurality of bearings comprises rolling bearing elements.

14. The earth-boring tool of claim 13 , wherein the rolling bearing elements comprise tapered rolling bearing elements.

15. The earth-boring tool of claim 13 , wherein the rolling bearing elements comprise cylindrical rolling bearing elements.

16. The earth-boring tool of claim 7 , wherein at least one of the first plurality of bearings and the second plurality of bearings comprises opposing sets of non-rolling bearing elements each including a volume of polycrystalline diamond material, the polycrystalline diamond material of a first set of the opposing sets configured to abut against and slide relative to the polycrystalline diamond material of a set of the opposing sets during operation of the bearing system.

17. The earth-boring tool of claim 7 , wherein the head washer is integrally formed with, and comprises an integral portion of the at least one head.

18. A method of forming an earth-boring tool configured for use in a subterranean formation, comprising:

inserting a tensioner bolt into a rolling cutter;

inserting a rolling cutter washer into the rolling cutter;

providing a plurality of bearings on the rolling cutter washer within the rolling cutter;

inserting a substantially planar shaft washer into the rolling cutter such that the bearings of the plurality of bearings are disposed between the rolling cutter washer and the at least substantially planar shaft washer;

providing a retaining member within the rolling cutter to retain the at least substantially planar shaft washer, the plurality of bearings, the rolling cutter washer, and the tensioner bolt within the rolling cutter;

positioning a head washer over and around a head of a tool body of the earth-boring tool;

providing an additional plurality of bearings on the head washer, such that the at least substantially planar shaft washer is directly interposed between, and in contact with, the bearings on the rolling cutter washer and the additional plurality of bearings on the head washer;

positioning the rolling cutter on the head such that the tensioner bolt extends through the head, and the plurality of bearings on the rolling cutter washer is disposed between the head washer and the at least substantially planar shaft washer retained within the rolling cutter; and

securing the tensioner bolt to the head to secure the rolling cutter to the head and tensioning the tensioner bolt to compress the additional plurality of bearings between the head washer and the at least substantially planar shaft washer, and to compress the plurality of bearings between the at least substantially planar shaft washer and the rolling cutter washer.

19. The method of claim 18 , further comprising selecting at least one of the plurality of bearings and the additional plurality of bearings to comprise rolling bearing elements.

20. The method of claim 19 , further comprising selecting the rolling bearing elements to comprise tapered rolling bearing elements.

21. The method of claim 19 , further comprising selecting the rolling bearing elements to comprise cylindrical rolling bearing elements.